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The First World War (WWI; 1914 to 1918) caused a substantial burden of injury and disease among participating military personnel. The most common injuries were caused by weapons (e.g., shrapnel from artillery, bullets and grenades). These injuries ranged from minor wounds up to those requiring limb amputations and causing permanent disability (e.g., blindness, deafness and traumatic brain injury).

Reviews have covered other health conditions in these personnel, including: the effects of the 1918 influenza pandemic on United States (US) and other soldiers;[[1,2]] the occurrence of malaria;[[3]] the (re)emergence of trench fever;[[4]] trench foot and other trench diseases;[[5,6]] and infectious diseases.[[7]] Reviews of mental health impacts have included the psychological effects on medical personnel involved,[[8]] shell shock and other psychoneuroses.[[9,10]]

For New Zealand, there were an estimated 98,950 military personnel who served overseas in WWI, and 7,036 who served on home territory in the New Zealand Expeditionary Force (NZEF) for a total of 105,986.[[11]] An estimated 18.2% died during the war and up to the end of 1923 (with this period used in the official New Zealand Roll of Honour[[11]]). The official number of personnel wounded or suffering illness was 41,317 (equivalent to 39.0% of NZEF personnel). However, this number included “all those removed from the front-line for medical treatment”, as well as including repeat hospitalisations of soldiers, so it was more “than the number of ‘wounded men’ per se”.[[11]]

These estimates do not include the more than 12,000 New Zealanders who served separately with other military forces during this war.[[12]] We also suspected that the official number of those wounded or suffering illness would be far below the level of overall morbidity that could be found upon examining military records for individual personnel—as found in a study of New Zealand personnel who served overseas in the South African War.[[13]]

The New Zealand military personnel were predominantly volunteers, though 26.0% were conscripted.[[14]] Previous studies of this military population have focussed on their overall lifespan,[[15–17]] but also aspects of their injury burden.[[18,19]] The infectious disease burden included that from pandemic influenza,[[20–23]] dysentery,[[24]] sexually transmitted infections[[25]] and disease outbreaks in training camps.[[26]] Other health aspects studied include the poor nutrition (e.g., at Gallipoli),[[27]] oral health[[28]] and mental health.[[29,30]] A wide range of health conditions were described in an official report published soon after the war[[31]] and a book details the medical services for the NZEF.[[32]] Other works cover a range of different health conditions.[[33–36]]

There is evidence of persisting disabilities after the war from the war pension data for New Zealand. As of 31 March 1921, a total of 40,227 veterans had lodged claims for war pensions for war-related disability and 17,612 dependents had also lodged war pension claims (for the period September 1915 to 1921).[[37]] Of all these claimants, 51,711 (or 89% of the total of 57,839) were granted war pensions (with this proportion not given separately for veterans vs dependents). Studies have also indicated elevated post-war morbidity in the veteran population. A cohort study following returned NZEF personnel across their remaining lifetimes found that 1.7% committed suicide.[[38]] Those who had been wounded, sick or medically discharged were found to have a significantly higher chance of suicide. Another study reported elevated suicide rates among these veterans compared to civilian men in the same age cohort during the 1920s and subsequent decades.[[39]] Other work has found death certificates of veterans that are suggestive of post-war deaths from suicide and alcoholism that could have been war related, along with deaths associated with operations on wounds and “war disability”.[[15]]

But despite all this work, it remains unclear what the overall injury/disease burden was for the New Zealand military personnel in this war. Similarly, for detail on the seriousness of the conditions e.g., as determined by hospitalisation. We therefore aimed to assess this burden with an in-depth examination of a random selection of military personnel from a national military force: that for Aotearoa New Zealand.

By way of further background, the NZEF mainly fought in Europe on the Western Front, but was also part of campaigns in the Middle East (Gallipoli and Palestine).[[40]] After its experience of fierce fighting at Gallipoli (1915), the newly formed New Zealand Division was sent to the Western Front in early 1916. It was initially assigned to a relatively quiet sector of the front at Armentières. This was to allow the troops to acclimatise and to familiarise themselves with the new warfare conditions on the Western Front. Following this, they were then dispatched to significant sectors of the Western Front, participating in major battles such as those at the Somme (1916), Messines (1917), Passchendaele (1917), the German Spring Offensive (1918) and the Hundred Days final offensive. These were among the most intense and pivotal campaigns of WWI. The last military action on the Western Front for the New Zealanders was the liberation of the town of Le Quesnoy (where the New Zealand Liberation Museum will be opened in October 2023). A map showing relevant areas for the New Zealand military on the Western Front is available here: https://nzhistory.govt.nz/media/photo/western-front-1916-17-map.

Methods

Sample selection

The sample was derived from a previous study on a random sample of NZEF participants in WWI.[[17]] From this larger sample we randomly selected 200 personnel for the in-depth analysis of their morbidity experience (for further details see the Appendix).

Data collection

All the socio-demographic data (including ethnicity and occupational class) were collected, as per the previously published study,[[17]] as were military rank and participation in previous and subsequent wars. Added to this were data on new diagnoses, hospitalisations for new conditions and discharges from the military on medical grounds (all from the online archive of military files[[41]]). These files were almost all hand-written, often in difficult conditions at battalion or similar level.

On occasions, the paucity of details in the military files on health conditions required some assumptions, as follows:

• Where a condition could plausibly have been related to subsequent relapses or sequelae, we did not count these sequelae conditions separately. For example, a reference to “debility” that was followed several months after “influenza” or “dysentery” was assumed to be sequelae of one of these earlier diagnoses.

• For hospitalisations, we also distinguished between those for new conditions as opposed to those related to transfers to other facilities (e.g., from hospital to convalescent facility) or ongoing treatment for a previously identified condition. We collected data on all admissions to hospitals, hospital ships and convalescent care facilities, but did not count visits to field ambulance units or casualty clearing stations that did not result in hospitalisation. To facilitate the data collection process, a detailed list of terms and acronyms used in the military files was compiled beforehand (see the Appendix).

• Where a particular diagnosis was first made after military service was completed e.g., a diagnosis of “shell shock” by a medical board after the war, we assumed that this condition had commenced while still in military service.

• The timing of “frontline” status was established by military file entries such as: “joined battalion” or battery or similar frontline unit (typically after periods in training or in the “rear”).

Other data sources that were occasionally consulted were online obituaries (e.g., in the dataset: Papers Past [https://paperspast.natlib.govt.nz/]).

Inter-observer reliability assessment for data collection

As the data extraction was first done by a single author, two other authors with experience in work with NZEF records each independently re-examined 10 randomly selected additional files each (to make up a 10% sample). The assessment compared the new diagnoses, the new hospitalisations and samples of extracted numerical data.

Data analysis

Data were collated in a Microsoft Excel file and univariate analyses were conducted using EpiInfo v7.1.5.2. Lifespan comparisons for different groups used analysis of variance (ANOVA).

Ethics statement

Ethical approval for this study was provided through the University of Otago Human Ethics Committee process (Category B Approval, D22/030).

Results

Inter-observer reliability assessment

Based on the two subsequent observers independently examining a 10% sample of the data, the following sensitivity estimates were obtained for the first and main observer (when the “true” denominator is assumed to be that from all observers combined): 89% (41/46) for the number of new conditions; 91% (39/43) for the number of hospitalisations for new conditions; 84% (21/25) for the number of war theatres; 100% (19/19) for the correct date of death (when available from this source); and 100% (20/20) for length of stay overseas. Errors were made by the main observer for an incorrect “unfit status” (5%, 1/19) and for one diagnosis (2%, 1/46, where the words disability and diabetes were confused with each other).

Characteristics of the studied population

The average age of this randomly selected sample was 25.4 years (at the start of the war) and they were nearly all of European ethnicity (i.e., only 2.5% were Māori) (Table 1). The occupational class was dominated by the lower three groupings (54%) and military rank was predominantly in the lowest rankings (88%). By the end of 1916, 48% had been to a frontline position, and by the end of the war, 91.5%. The mean length of war participation was 2.6 years and the most common theatres of war were the Western Front (74%) and then the Middle East (Egypt, Sinai and Palestine) at 22%.

View Tables 1–4, Figure 1.

Morbidity burden

The great majority (94%) of this study population had at least one non-fatal new condition diagnosed and 89% had at least one hospitalisation for a new condition (Table 2). Indeed, the average participant had 2.4 new diagnoses and 1.8 hospitalisations for new conditions during their military service. This equated to 0.9 new conditions and 0.7 hospitalisations for new conditions per year of military service.

In terms of specific conditions, 42% of the personnel experienced at least one conflict-associated injury event (Table 3; Figure 1). Injuries from chemical warfare (gas poisoning) were experienced by 6% of personnel. But most of the new diagnoses were for infectious diseases, followed by the grouping of “other causes” (e.g., mental health) and then conflict-related injuries (117, 74 and 50 cases per 100 personnel respectively).

Respiratory conditions (including influenza, pneumonia, bronchitis and tuberculosis) alone impacted around a third of personnel (33%), with influenza being diagnosed in 19%. Sexually transmitted infections affected 14% of personnel (16 cases per 100 personnel), with gonorrhoea being the most common specified type.

Diseases typically reflecting hazardous environmental conditions were relatively common e.g., for dysentery/gastroenteritis at 12% and scabies at 5% of personnel. Less common were “trench” diseases (i.e., trench fever, trench foot, trench mouth), and there were no identified cases of typhoid and typhus.

Diagnoses suggestive of post-traumatic stress disorder (PTSD) were present in 10% of the personnel (9.5 cases per 100 personnel). The most common term used was “disordered action of the heart” (DAH), followed by neurasthenia and shell shock.

Due to either injuries or illnesses, most of the personnel were deemed “unfit for military service” by a military medical board (59%) at some point in their military service (Table 3).

Associations between morbidity and lifespan

The comparisons in Table 4 suggest no statistically significant differences between the various groups. Nevertheless, the pattern was for slightly lower lifespan among those with more diagnosed new conditions, more hospitalisations for new conditions, having had a STI diagnosis and being declared unfit at some point. The exception was for having a mental health diagnosis, which was associated with a slightly higher lifespan (albeit also not statistically significant).

Discussion

Main findings and interpretation

The major finding of this work was the very high morbidity burden of this military force—with 94% having at least one new condition diagnosed. The high level of personnel hospitalised (89%) also attests to the relative severity of most conditions, as does the majority (59%) of personnel being deemed no longer fit for further military service at some stage. These high proportions contrast with the official number of personnel wounded or suffering illness as detailed in the Introduction (41,317 personnel, equivalent to 39% of all NZEF personnel).

However, our estimate for diagnosed conditions will still be an under-estimate as it will not have captured more minor conditions. For example, nearly all of these personnel probably had a lice infestation[[35]] and many would have had symptomatic influenza during the pandemic in 1918–1919[[22]] without it necessarily being recorded in the military files. We also did not count as hospitalisations the admissions to field ambulance units or casualty clearing stations, some of which were for several days, if the soldier returned to the unit.

That infectious disease diagnoses were over twice as common as conflict-related injuries (117 vs 50 cases per 100 personnel respectively) is in contrast to the mortality burden for the NZEF in this war. That is, direct conflict-related deaths were 89% of all deaths compared to 8% dying of “disease”.[[18]] But in the preceding war involving New Zealand military personnel (the South African War), 59% of deaths were from disease.[[13]]

Condition severity was sometimes such that injuries were likely to have resulted in life-long disabilities (e.g., for head injuries and amputations). One of the personnel in this study had severe facial injuries that was officially deemed a factor in his suicide soon after the war. Some of the various infectious diseases listed in Table 3 could also result in adverse long-term sequalae e.g., tuberculosis, syphilis and malaria. Fortunately, there were no cases of typhoid identified in this sample, possibly a reflection of most of these personnel being vaccinated against it. Similarly, there were no cases of typhus, which was a major cause of death in Eastern Europe during this war.[[7]]

The overall cumulative incidence of STIs in this study (16 cases per 100 personnel) was fairly similar to that estimated previously by an Australian medical historian: at 130 per 1,000 for New Zealand personnel vs 158 per 1,000 for Australian personnel.[[35]] Further work is needed to estimate if such differences by country related to efforts by New Zealand military leadership in STI control, along with the advocacy efforts of Ettie Rout,[[42]] which contributed to condom distribution from late 1917.

The finding of 10% of personnel being given a likely PTSD diagnosis is also probably an under-estimate, given how this condition was poorly understood at the time.[[29]] Indeed, a study of Vietnam War veterans in New Zealand reported that 20% had PTSD.[[43]] A more recent study of serving and retired New Zealand military personnel identified 30% with scores indicative of post-traumatic stress.[[44]]

None of the lifespan results in this study provide statistical evidence of a link with morbidity experiences during the war. But the results were generally in the direction of such an association and so larger studies could consider exploring these issues further. An Australian study of WWI veterans did find statistically significant increased mortality after 1921 for those who were: discharged as medically unfit, discharged as partially/totally permanently disabled and being discharged due to “venereal disease”.[[45]]

Study strengths and limitations

A strength of this study is that it is the first relatively in-depth analysis of morbidity in a random sample of New Zealand military participants of WWI (to our knowledge). The research benefitted from the individual military records being available online and from the researchers having extensive experience (from previous studies) in interpreting the archival military records of the NZEF, knowledge of the WWI military environment and knowledge of medical terminology. Nevertheless, various limitations with our study need to be considered. In particular:

• Despite involving random sampling, the study sample was only “fairly representative” of all military personnel in the NZEF given various exclusions. These exclusions are detailed further in the Appendix, but the major ones involved not going overseas to fight, being female, being Pasifika, and not surviving the war. As such it does not reflect the morbidity experience of these particular groups (and indeed, those killed in the war could also have had a worse morbidity profile in the period up until their deaths than other participants).

• We could not account for conditions not detailed in the military files. This under-recording was probably common, especially for more minor conditions that did not involve treatment by medical personnel (e.g., lice infestation and milder cases of pandemic influenza as discussed above). Indeed, one New Zealand soldier contributed a satirical poem to the “Chronicles of the N.Z.E.F” about the how wounded men were entitled to wear a gold stripe on the left sleeve, yet there was no formal recognition for “little ills” like “dysent’ry”, fever, septic sores, shell shock, frost-bite, rotting feet and being gassed.[[46]] Also, some conditions may not have been self-reported (e.g., symptoms of a STI) given the punitive approaches that could be taken by the military authorities.[[25]] Similarly, such “sensitive” diagnoses relating to STIs or mental health may have not been recorded by staff on purpose, so as to protect the reputation and future career of the patient. Finally, dental records were relatively sparse in the individual military files, suggestive that such records were held separately.

• There was a lack of specificity to some of the conditions as shown by the “pyrexia of unknown origin” category in Table 3. Such fever symptoms could have potentially arisen from many different infectious diseases.

• We may have missed some relevant data due to misinterpreting the hand-written text/acronyms/abbreviations in the archival military files. This is because of the highly cursive handwriting styles typically used and due to the complexity of some of the records (e.g., one was 189 pages long, and some were mixed up with WWII records). Nevertheless, the inter-observer assessment study suggested reasonable results for sensitivity and specificity to the extent these can be estimated. Indeed, the values (such as 84% for the lowest end of the sensitivity range) might be under-estimates since the first author also did subsequent logic checks on the entire dataset and identified additional data items that could then be included in the final dataset version.

Possible lessons for governments and further research possibilities

It has taken over 100 years for the morbidity burden for WWI personnel to be established in terms of new conditions and hospitalisations for new conditions. This highlights the need for governments to properly document such health burdens from past wars. Such documentation could better inform the need for conflict prevention (e.g., via diplomacy) as well as for ongoing maintenance of high health status among serving military personnel, provisioning them with appropriate equipment and ensuring high-quality medical services to protect and treat them.

Further research could be done, including studies that explore the relationship between health conditions and the proximity to frontline combat in various theatres of WWI. Similarly for health risks associated with different roles in the military (e.g., being a health worker, being a private or officer, etc.) and for cross-country comparisons (e.g., New Zealand vs Australian military personnel). Māori or Pasifika researchers could also be funded to study the health burden in a random sample of these ethnic groups of military personnel.

Conclusions

The overall morbidity burden of this military force in WWI was very high, and much higher than the previous official estimates. A wide range of conditions were found in this study, but as with preceding conflicts the cases of infectious diseases were more frequent than those from conflict-related injuries.

View Appendix.

Summary

Abstract

Aim

Studies of the morbidity burden of military personnel participating in the First World War (WWI) have tended to focus on specific outcomes (e.g., injuries). Therefore, we aimed for a more complete assessment.

Method

From a random sample of active war service-exposed New Zealand WWI veterans used in previously published work, we examined a random subsample of 200 personnel. Data on diagnoses, hospitalisations and outcomes were extracted from the online archival military files.

Results

These personnel experienced a very high morbidity burden with 94% having at least one new condition diagnosed during their military service (mean: 2.4 per individual; range: 0 to 8). The relative severity of these conditions was reflected by the high level of hospitalisation (89% at least once; mean: 1.8 hospitalisations for new conditions per individual) and 59% of personnel being deemed no longer fit for military service at some stage. More of the new diagnoses were for infectious diseases than for conflict-related injuries (117 vs 50 cases per 100 personnel).  Respiratory conditions such as influenza, pneumonia and tuberculosis affected 33% of personnel, and 14% were diagnosed with sexually transmitted infections. Diseases reflecting hazardous environmental conditions were relatively common e.g., for dysentery/gastroenteritis in 12% and scabies in 5% of personnel. Diagnoses suggestive of post-traumatic stress disorder (PTSD) were present in 10% and chemical warfare injuries in 6%.

Conclusion

The overall morbidity burden of this military force in WWI was very high, and much higher than the previous official estimates.

Author Information

Nick Wilson: Department of Public Health, University of Otago Wellington, New Zealand. Jennifer A Summers: Department of Public Health, University of Otago Wellington, New Zealand. Glyn Harper: Massey University, Palmerston North, New Zealand. George Thomson: Department of Public Health, University of Otago Wellington, New Zealand.

Acknowledgements

The authors thank Christine Clement (genealogist) for assistance with determining the dates of birth and death for this cohort. Auckland War Memorial Museum kindly provided a copy of the Cenotaph records that assisted with sampling.

Correspondence

Professor Nick Wilson: Department of Public Health, University of Otago Wellington, Mein St, Newtown, Wellington, New Zealand.

Correspondence Email

nick.wilson@otago.ac.nz

Competing Interests

None declared.

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The First World War (WWI; 1914 to 1918) caused a substantial burden of injury and disease among participating military personnel. The most common injuries were caused by weapons (e.g., shrapnel from artillery, bullets and grenades). These injuries ranged from minor wounds up to those requiring limb amputations and causing permanent disability (e.g., blindness, deafness and traumatic brain injury).

Reviews have covered other health conditions in these personnel, including: the effects of the 1918 influenza pandemic on United States (US) and other soldiers;[[1,2]] the occurrence of malaria;[[3]] the (re)emergence of trench fever;[[4]] trench foot and other trench diseases;[[5,6]] and infectious diseases.[[7]] Reviews of mental health impacts have included the psychological effects on medical personnel involved,[[8]] shell shock and other psychoneuroses.[[9,10]]

For New Zealand, there were an estimated 98,950 military personnel who served overseas in WWI, and 7,036 who served on home territory in the New Zealand Expeditionary Force (NZEF) for a total of 105,986.[[11]] An estimated 18.2% died during the war and up to the end of 1923 (with this period used in the official New Zealand Roll of Honour[[11]]). The official number of personnel wounded or suffering illness was 41,317 (equivalent to 39.0% of NZEF personnel). However, this number included “all those removed from the front-line for medical treatment”, as well as including repeat hospitalisations of soldiers, so it was more “than the number of ‘wounded men’ per se”.[[11]]

These estimates do not include the more than 12,000 New Zealanders who served separately with other military forces during this war.[[12]] We also suspected that the official number of those wounded or suffering illness would be far below the level of overall morbidity that could be found upon examining military records for individual personnel—as found in a study of New Zealand personnel who served overseas in the South African War.[[13]]

The New Zealand military personnel were predominantly volunteers, though 26.0% were conscripted.[[14]] Previous studies of this military population have focussed on their overall lifespan,[[15–17]] but also aspects of their injury burden.[[18,19]] The infectious disease burden included that from pandemic influenza,[[20–23]] dysentery,[[24]] sexually transmitted infections[[25]] and disease outbreaks in training camps.[[26]] Other health aspects studied include the poor nutrition (e.g., at Gallipoli),[[27]] oral health[[28]] and mental health.[[29,30]] A wide range of health conditions were described in an official report published soon after the war[[31]] and a book details the medical services for the NZEF.[[32]] Other works cover a range of different health conditions.[[33–36]]

There is evidence of persisting disabilities after the war from the war pension data for New Zealand. As of 31 March 1921, a total of 40,227 veterans had lodged claims for war pensions for war-related disability and 17,612 dependents had also lodged war pension claims (for the period September 1915 to 1921).[[37]] Of all these claimants, 51,711 (or 89% of the total of 57,839) were granted war pensions (with this proportion not given separately for veterans vs dependents). Studies have also indicated elevated post-war morbidity in the veteran population. A cohort study following returned NZEF personnel across their remaining lifetimes found that 1.7% committed suicide.[[38]] Those who had been wounded, sick or medically discharged were found to have a significantly higher chance of suicide. Another study reported elevated suicide rates among these veterans compared to civilian men in the same age cohort during the 1920s and subsequent decades.[[39]] Other work has found death certificates of veterans that are suggestive of post-war deaths from suicide and alcoholism that could have been war related, along with deaths associated with operations on wounds and “war disability”.[[15]]

But despite all this work, it remains unclear what the overall injury/disease burden was for the New Zealand military personnel in this war. Similarly, for detail on the seriousness of the conditions e.g., as determined by hospitalisation. We therefore aimed to assess this burden with an in-depth examination of a random selection of military personnel from a national military force: that for Aotearoa New Zealand.

By way of further background, the NZEF mainly fought in Europe on the Western Front, but was also part of campaigns in the Middle East (Gallipoli and Palestine).[[40]] After its experience of fierce fighting at Gallipoli (1915), the newly formed New Zealand Division was sent to the Western Front in early 1916. It was initially assigned to a relatively quiet sector of the front at Armentières. This was to allow the troops to acclimatise and to familiarise themselves with the new warfare conditions on the Western Front. Following this, they were then dispatched to significant sectors of the Western Front, participating in major battles such as those at the Somme (1916), Messines (1917), Passchendaele (1917), the German Spring Offensive (1918) and the Hundred Days final offensive. These were among the most intense and pivotal campaigns of WWI. The last military action on the Western Front for the New Zealanders was the liberation of the town of Le Quesnoy (where the New Zealand Liberation Museum will be opened in October 2023). A map showing relevant areas for the New Zealand military on the Western Front is available here: https://nzhistory.govt.nz/media/photo/western-front-1916-17-map.

Methods

Sample selection

The sample was derived from a previous study on a random sample of NZEF participants in WWI.[[17]] From this larger sample we randomly selected 200 personnel for the in-depth analysis of their morbidity experience (for further details see the Appendix).

Data collection

All the socio-demographic data (including ethnicity and occupational class) were collected, as per the previously published study,[[17]] as were military rank and participation in previous and subsequent wars. Added to this were data on new diagnoses, hospitalisations for new conditions and discharges from the military on medical grounds (all from the online archive of military files[[41]]). These files were almost all hand-written, often in difficult conditions at battalion or similar level.

On occasions, the paucity of details in the military files on health conditions required some assumptions, as follows:

• Where a condition could plausibly have been related to subsequent relapses or sequelae, we did not count these sequelae conditions separately. For example, a reference to “debility” that was followed several months after “influenza” or “dysentery” was assumed to be sequelae of one of these earlier diagnoses.

• For hospitalisations, we also distinguished between those for new conditions as opposed to those related to transfers to other facilities (e.g., from hospital to convalescent facility) or ongoing treatment for a previously identified condition. We collected data on all admissions to hospitals, hospital ships and convalescent care facilities, but did not count visits to field ambulance units or casualty clearing stations that did not result in hospitalisation. To facilitate the data collection process, a detailed list of terms and acronyms used in the military files was compiled beforehand (see the Appendix).

• Where a particular diagnosis was first made after military service was completed e.g., a diagnosis of “shell shock” by a medical board after the war, we assumed that this condition had commenced while still in military service.

• The timing of “frontline” status was established by military file entries such as: “joined battalion” or battery or similar frontline unit (typically after periods in training or in the “rear”).

Other data sources that were occasionally consulted were online obituaries (e.g., in the dataset: Papers Past [https://paperspast.natlib.govt.nz/]).

Inter-observer reliability assessment for data collection

As the data extraction was first done by a single author, two other authors with experience in work with NZEF records each independently re-examined 10 randomly selected additional files each (to make up a 10% sample). The assessment compared the new diagnoses, the new hospitalisations and samples of extracted numerical data.

Data analysis

Data were collated in a Microsoft Excel file and univariate analyses were conducted using EpiInfo v7.1.5.2. Lifespan comparisons for different groups used analysis of variance (ANOVA).

Ethics statement

Ethical approval for this study was provided through the University of Otago Human Ethics Committee process (Category B Approval, D22/030).

Results

Inter-observer reliability assessment

Based on the two subsequent observers independently examining a 10% sample of the data, the following sensitivity estimates were obtained for the first and main observer (when the “true” denominator is assumed to be that from all observers combined): 89% (41/46) for the number of new conditions; 91% (39/43) for the number of hospitalisations for new conditions; 84% (21/25) for the number of war theatres; 100% (19/19) for the correct date of death (when available from this source); and 100% (20/20) for length of stay overseas. Errors were made by the main observer for an incorrect “unfit status” (5%, 1/19) and for one diagnosis (2%, 1/46, where the words disability and diabetes were confused with each other).

Characteristics of the studied population

The average age of this randomly selected sample was 25.4 years (at the start of the war) and they were nearly all of European ethnicity (i.e., only 2.5% were Māori) (Table 1). The occupational class was dominated by the lower three groupings (54%) and military rank was predominantly in the lowest rankings (88%). By the end of 1916, 48% had been to a frontline position, and by the end of the war, 91.5%. The mean length of war participation was 2.6 years and the most common theatres of war were the Western Front (74%) and then the Middle East (Egypt, Sinai and Palestine) at 22%.

View Tables 1–4, Figure 1.

Morbidity burden

The great majority (94%) of this study population had at least one non-fatal new condition diagnosed and 89% had at least one hospitalisation for a new condition (Table 2). Indeed, the average participant had 2.4 new diagnoses and 1.8 hospitalisations for new conditions during their military service. This equated to 0.9 new conditions and 0.7 hospitalisations for new conditions per year of military service.

In terms of specific conditions, 42% of the personnel experienced at least one conflict-associated injury event (Table 3; Figure 1). Injuries from chemical warfare (gas poisoning) were experienced by 6% of personnel. But most of the new diagnoses were for infectious diseases, followed by the grouping of “other causes” (e.g., mental health) and then conflict-related injuries (117, 74 and 50 cases per 100 personnel respectively).

Respiratory conditions (including influenza, pneumonia, bronchitis and tuberculosis) alone impacted around a third of personnel (33%), with influenza being diagnosed in 19%. Sexually transmitted infections affected 14% of personnel (16 cases per 100 personnel), with gonorrhoea being the most common specified type.

Diseases typically reflecting hazardous environmental conditions were relatively common e.g., for dysentery/gastroenteritis at 12% and scabies at 5% of personnel. Less common were “trench” diseases (i.e., trench fever, trench foot, trench mouth), and there were no identified cases of typhoid and typhus.

Diagnoses suggestive of post-traumatic stress disorder (PTSD) were present in 10% of the personnel (9.5 cases per 100 personnel). The most common term used was “disordered action of the heart” (DAH), followed by neurasthenia and shell shock.

Due to either injuries or illnesses, most of the personnel were deemed “unfit for military service” by a military medical board (59%) at some point in their military service (Table 3).

Associations between morbidity and lifespan

The comparisons in Table 4 suggest no statistically significant differences between the various groups. Nevertheless, the pattern was for slightly lower lifespan among those with more diagnosed new conditions, more hospitalisations for new conditions, having had a STI diagnosis and being declared unfit at some point. The exception was for having a mental health diagnosis, which was associated with a slightly higher lifespan (albeit also not statistically significant).

Discussion

Main findings and interpretation

The major finding of this work was the very high morbidity burden of this military force—with 94% having at least one new condition diagnosed. The high level of personnel hospitalised (89%) also attests to the relative severity of most conditions, as does the majority (59%) of personnel being deemed no longer fit for further military service at some stage. These high proportions contrast with the official number of personnel wounded or suffering illness as detailed in the Introduction (41,317 personnel, equivalent to 39% of all NZEF personnel).

However, our estimate for diagnosed conditions will still be an under-estimate as it will not have captured more minor conditions. For example, nearly all of these personnel probably had a lice infestation[[35]] and many would have had symptomatic influenza during the pandemic in 1918–1919[[22]] without it necessarily being recorded in the military files. We also did not count as hospitalisations the admissions to field ambulance units or casualty clearing stations, some of which were for several days, if the soldier returned to the unit.

That infectious disease diagnoses were over twice as common as conflict-related injuries (117 vs 50 cases per 100 personnel respectively) is in contrast to the mortality burden for the NZEF in this war. That is, direct conflict-related deaths were 89% of all deaths compared to 8% dying of “disease”.[[18]] But in the preceding war involving New Zealand military personnel (the South African War), 59% of deaths were from disease.[[13]]

Condition severity was sometimes such that injuries were likely to have resulted in life-long disabilities (e.g., for head injuries and amputations). One of the personnel in this study had severe facial injuries that was officially deemed a factor in his suicide soon after the war. Some of the various infectious diseases listed in Table 3 could also result in adverse long-term sequalae e.g., tuberculosis, syphilis and malaria. Fortunately, there were no cases of typhoid identified in this sample, possibly a reflection of most of these personnel being vaccinated against it. Similarly, there were no cases of typhus, which was a major cause of death in Eastern Europe during this war.[[7]]

The overall cumulative incidence of STIs in this study (16 cases per 100 personnel) was fairly similar to that estimated previously by an Australian medical historian: at 130 per 1,000 for New Zealand personnel vs 158 per 1,000 for Australian personnel.[[35]] Further work is needed to estimate if such differences by country related to efforts by New Zealand military leadership in STI control, along with the advocacy efforts of Ettie Rout,[[42]] which contributed to condom distribution from late 1917.

The finding of 10% of personnel being given a likely PTSD diagnosis is also probably an under-estimate, given how this condition was poorly understood at the time.[[29]] Indeed, a study of Vietnam War veterans in New Zealand reported that 20% had PTSD.[[43]] A more recent study of serving and retired New Zealand military personnel identified 30% with scores indicative of post-traumatic stress.[[44]]

None of the lifespan results in this study provide statistical evidence of a link with morbidity experiences during the war. But the results were generally in the direction of such an association and so larger studies could consider exploring these issues further. An Australian study of WWI veterans did find statistically significant increased mortality after 1921 for those who were: discharged as medically unfit, discharged as partially/totally permanently disabled and being discharged due to “venereal disease”.[[45]]

Study strengths and limitations

A strength of this study is that it is the first relatively in-depth analysis of morbidity in a random sample of New Zealand military participants of WWI (to our knowledge). The research benefitted from the individual military records being available online and from the researchers having extensive experience (from previous studies) in interpreting the archival military records of the NZEF, knowledge of the WWI military environment and knowledge of medical terminology. Nevertheless, various limitations with our study need to be considered. In particular:

• Despite involving random sampling, the study sample was only “fairly representative” of all military personnel in the NZEF given various exclusions. These exclusions are detailed further in the Appendix, but the major ones involved not going overseas to fight, being female, being Pasifika, and not surviving the war. As such it does not reflect the morbidity experience of these particular groups (and indeed, those killed in the war could also have had a worse morbidity profile in the period up until their deaths than other participants).

• We could not account for conditions not detailed in the military files. This under-recording was probably common, especially for more minor conditions that did not involve treatment by medical personnel (e.g., lice infestation and milder cases of pandemic influenza as discussed above). Indeed, one New Zealand soldier contributed a satirical poem to the “Chronicles of the N.Z.E.F” about the how wounded men were entitled to wear a gold stripe on the left sleeve, yet there was no formal recognition for “little ills” like “dysent’ry”, fever, septic sores, shell shock, frost-bite, rotting feet and being gassed.[[46]] Also, some conditions may not have been self-reported (e.g., symptoms of a STI) given the punitive approaches that could be taken by the military authorities.[[25]] Similarly, such “sensitive” diagnoses relating to STIs or mental health may have not been recorded by staff on purpose, so as to protect the reputation and future career of the patient. Finally, dental records were relatively sparse in the individual military files, suggestive that such records were held separately.

• There was a lack of specificity to some of the conditions as shown by the “pyrexia of unknown origin” category in Table 3. Such fever symptoms could have potentially arisen from many different infectious diseases.

• We may have missed some relevant data due to misinterpreting the hand-written text/acronyms/abbreviations in the archival military files. This is because of the highly cursive handwriting styles typically used and due to the complexity of some of the records (e.g., one was 189 pages long, and some were mixed up with WWII records). Nevertheless, the inter-observer assessment study suggested reasonable results for sensitivity and specificity to the extent these can be estimated. Indeed, the values (such as 84% for the lowest end of the sensitivity range) might be under-estimates since the first author also did subsequent logic checks on the entire dataset and identified additional data items that could then be included in the final dataset version.

Possible lessons for governments and further research possibilities

It has taken over 100 years for the morbidity burden for WWI personnel to be established in terms of new conditions and hospitalisations for new conditions. This highlights the need for governments to properly document such health burdens from past wars. Such documentation could better inform the need for conflict prevention (e.g., via diplomacy) as well as for ongoing maintenance of high health status among serving military personnel, provisioning them with appropriate equipment and ensuring high-quality medical services to protect and treat them.

Further research could be done, including studies that explore the relationship between health conditions and the proximity to frontline combat in various theatres of WWI. Similarly for health risks associated with different roles in the military (e.g., being a health worker, being a private or officer, etc.) and for cross-country comparisons (e.g., New Zealand vs Australian military personnel). Māori or Pasifika researchers could also be funded to study the health burden in a random sample of these ethnic groups of military personnel.

Conclusions

The overall morbidity burden of this military force in WWI was very high, and much higher than the previous official estimates. A wide range of conditions were found in this study, but as with preceding conflicts the cases of infectious diseases were more frequent than those from conflict-related injuries.

View Appendix.

Summary

Abstract

Aim

Studies of the morbidity burden of military personnel participating in the First World War (WWI) have tended to focus on specific outcomes (e.g., injuries). Therefore, we aimed for a more complete assessment.

Method

From a random sample of active war service-exposed New Zealand WWI veterans used in previously published work, we examined a random subsample of 200 personnel. Data on diagnoses, hospitalisations and outcomes were extracted from the online archival military files.

Results

These personnel experienced a very high morbidity burden with 94% having at least one new condition diagnosed during their military service (mean: 2.4 per individual; range: 0 to 8). The relative severity of these conditions was reflected by the high level of hospitalisation (89% at least once; mean: 1.8 hospitalisations for new conditions per individual) and 59% of personnel being deemed no longer fit for military service at some stage. More of the new diagnoses were for infectious diseases than for conflict-related injuries (117 vs 50 cases per 100 personnel).  Respiratory conditions such as influenza, pneumonia and tuberculosis affected 33% of personnel, and 14% were diagnosed with sexually transmitted infections. Diseases reflecting hazardous environmental conditions were relatively common e.g., for dysentery/gastroenteritis in 12% and scabies in 5% of personnel. Diagnoses suggestive of post-traumatic stress disorder (PTSD) were present in 10% and chemical warfare injuries in 6%.

Conclusion

The overall morbidity burden of this military force in WWI was very high, and much higher than the previous official estimates.

Author Information

Nick Wilson: Department of Public Health, University of Otago Wellington, New Zealand. Jennifer A Summers: Department of Public Health, University of Otago Wellington, New Zealand. Glyn Harper: Massey University, Palmerston North, New Zealand. George Thomson: Department of Public Health, University of Otago Wellington, New Zealand.

Acknowledgements

The authors thank Christine Clement (genealogist) for assistance with determining the dates of birth and death for this cohort. Auckland War Memorial Museum kindly provided a copy of the Cenotaph records that assisted with sampling.

Correspondence

Professor Nick Wilson: Department of Public Health, University of Otago Wellington, Mein St, Newtown, Wellington, New Zealand.

Correspondence Email

nick.wilson@otago.ac.nz

Competing Interests

None declared.

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14) Statistics New Zealand. The New Zealand Official Year-book 1919 [Internet]. Wellington, New Zealand: Census and Statistics Office; 1920 [cited 2023 Jul 2].  Available from: https://www3.stats.govt.nz/New_Zealand_Official_Yearbooks/1919/NZOYB_1919.html.

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16) Wilson N, Boyd M, Nisa S, et al. Did exposure to a severe outbreak of pandemic influenza in 1918 impact on long-term survival? Epidemiol Infect. 2016;144(15):3166-69. Doi: 10.1017/S0950268816001606.

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The First World War (WWI; 1914 to 1918) caused a substantial burden of injury and disease among participating military personnel. The most common injuries were caused by weapons (e.g., shrapnel from artillery, bullets and grenades). These injuries ranged from minor wounds up to those requiring limb amputations and causing permanent disability (e.g., blindness, deafness and traumatic brain injury).

Reviews have covered other health conditions in these personnel, including: the effects of the 1918 influenza pandemic on United States (US) and other soldiers;[[1,2]] the occurrence of malaria;[[3]] the (re)emergence of trench fever;[[4]] trench foot and other trench diseases;[[5,6]] and infectious diseases.[[7]] Reviews of mental health impacts have included the psychological effects on medical personnel involved,[[8]] shell shock and other psychoneuroses.[[9,10]]

For New Zealand, there were an estimated 98,950 military personnel who served overseas in WWI, and 7,036 who served on home territory in the New Zealand Expeditionary Force (NZEF) for a total of 105,986.[[11]] An estimated 18.2% died during the war and up to the end of 1923 (with this period used in the official New Zealand Roll of Honour[[11]]). The official number of personnel wounded or suffering illness was 41,317 (equivalent to 39.0% of NZEF personnel). However, this number included “all those removed from the front-line for medical treatment”, as well as including repeat hospitalisations of soldiers, so it was more “than the number of ‘wounded men’ per se”.[[11]]

These estimates do not include the more than 12,000 New Zealanders who served separately with other military forces during this war.[[12]] We also suspected that the official number of those wounded or suffering illness would be far below the level of overall morbidity that could be found upon examining military records for individual personnel—as found in a study of New Zealand personnel who served overseas in the South African War.[[13]]

The New Zealand military personnel were predominantly volunteers, though 26.0% were conscripted.[[14]] Previous studies of this military population have focussed on their overall lifespan,[[15–17]] but also aspects of their injury burden.[[18,19]] The infectious disease burden included that from pandemic influenza,[[20–23]] dysentery,[[24]] sexually transmitted infections[[25]] and disease outbreaks in training camps.[[26]] Other health aspects studied include the poor nutrition (e.g., at Gallipoli),[[27]] oral health[[28]] and mental health.[[29,30]] A wide range of health conditions were described in an official report published soon after the war[[31]] and a book details the medical services for the NZEF.[[32]] Other works cover a range of different health conditions.[[33–36]]

There is evidence of persisting disabilities after the war from the war pension data for New Zealand. As of 31 March 1921, a total of 40,227 veterans had lodged claims for war pensions for war-related disability and 17,612 dependents had also lodged war pension claims (for the period September 1915 to 1921).[[37]] Of all these claimants, 51,711 (or 89% of the total of 57,839) were granted war pensions (with this proportion not given separately for veterans vs dependents). Studies have also indicated elevated post-war morbidity in the veteran population. A cohort study following returned NZEF personnel across their remaining lifetimes found that 1.7% committed suicide.[[38]] Those who had been wounded, sick or medically discharged were found to have a significantly higher chance of suicide. Another study reported elevated suicide rates among these veterans compared to civilian men in the same age cohort during the 1920s and subsequent decades.[[39]] Other work has found death certificates of veterans that are suggestive of post-war deaths from suicide and alcoholism that could have been war related, along with deaths associated with operations on wounds and “war disability”.[[15]]

But despite all this work, it remains unclear what the overall injury/disease burden was for the New Zealand military personnel in this war. Similarly, for detail on the seriousness of the conditions e.g., as determined by hospitalisation. We therefore aimed to assess this burden with an in-depth examination of a random selection of military personnel from a national military force: that for Aotearoa New Zealand.

By way of further background, the NZEF mainly fought in Europe on the Western Front, but was also part of campaigns in the Middle East (Gallipoli and Palestine).[[40]] After its experience of fierce fighting at Gallipoli (1915), the newly formed New Zealand Division was sent to the Western Front in early 1916. It was initially assigned to a relatively quiet sector of the front at Armentières. This was to allow the troops to acclimatise and to familiarise themselves with the new warfare conditions on the Western Front. Following this, they were then dispatched to significant sectors of the Western Front, participating in major battles such as those at the Somme (1916), Messines (1917), Passchendaele (1917), the German Spring Offensive (1918) and the Hundred Days final offensive. These were among the most intense and pivotal campaigns of WWI. The last military action on the Western Front for the New Zealanders was the liberation of the town of Le Quesnoy (where the New Zealand Liberation Museum will be opened in October 2023). A map showing relevant areas for the New Zealand military on the Western Front is available here: https://nzhistory.govt.nz/media/photo/western-front-1916-17-map.

Methods

Sample selection

The sample was derived from a previous study on a random sample of NZEF participants in WWI.[[17]] From this larger sample we randomly selected 200 personnel for the in-depth analysis of their morbidity experience (for further details see the Appendix).

Data collection

All the socio-demographic data (including ethnicity and occupational class) were collected, as per the previously published study,[[17]] as were military rank and participation in previous and subsequent wars. Added to this were data on new diagnoses, hospitalisations for new conditions and discharges from the military on medical grounds (all from the online archive of military files[[41]]). These files were almost all hand-written, often in difficult conditions at battalion or similar level.

On occasions, the paucity of details in the military files on health conditions required some assumptions, as follows:

• Where a condition could plausibly have been related to subsequent relapses or sequelae, we did not count these sequelae conditions separately. For example, a reference to “debility” that was followed several months after “influenza” or “dysentery” was assumed to be sequelae of one of these earlier diagnoses.

• For hospitalisations, we also distinguished between those for new conditions as opposed to those related to transfers to other facilities (e.g., from hospital to convalescent facility) or ongoing treatment for a previously identified condition. We collected data on all admissions to hospitals, hospital ships and convalescent care facilities, but did not count visits to field ambulance units or casualty clearing stations that did not result in hospitalisation. To facilitate the data collection process, a detailed list of terms and acronyms used in the military files was compiled beforehand (see the Appendix).

• Where a particular diagnosis was first made after military service was completed e.g., a diagnosis of “shell shock” by a medical board after the war, we assumed that this condition had commenced while still in military service.

• The timing of “frontline” status was established by military file entries such as: “joined battalion” or battery or similar frontline unit (typically after periods in training or in the “rear”).

Other data sources that were occasionally consulted were online obituaries (e.g., in the dataset: Papers Past [https://paperspast.natlib.govt.nz/]).

Inter-observer reliability assessment for data collection

As the data extraction was first done by a single author, two other authors with experience in work with NZEF records each independently re-examined 10 randomly selected additional files each (to make up a 10% sample). The assessment compared the new diagnoses, the new hospitalisations and samples of extracted numerical data.

Data analysis

Data were collated in a Microsoft Excel file and univariate analyses were conducted using EpiInfo v7.1.5.2. Lifespan comparisons for different groups used analysis of variance (ANOVA).

Ethics statement

Ethical approval for this study was provided through the University of Otago Human Ethics Committee process (Category B Approval, D22/030).

Results

Inter-observer reliability assessment

Based on the two subsequent observers independently examining a 10% sample of the data, the following sensitivity estimates were obtained for the first and main observer (when the “true” denominator is assumed to be that from all observers combined): 89% (41/46) for the number of new conditions; 91% (39/43) for the number of hospitalisations for new conditions; 84% (21/25) for the number of war theatres; 100% (19/19) for the correct date of death (when available from this source); and 100% (20/20) for length of stay overseas. Errors were made by the main observer for an incorrect “unfit status” (5%, 1/19) and for one diagnosis (2%, 1/46, where the words disability and diabetes were confused with each other).

Characteristics of the studied population

The average age of this randomly selected sample was 25.4 years (at the start of the war) and they were nearly all of European ethnicity (i.e., only 2.5% were Māori) (Table 1). The occupational class was dominated by the lower three groupings (54%) and military rank was predominantly in the lowest rankings (88%). By the end of 1916, 48% had been to a frontline position, and by the end of the war, 91.5%. The mean length of war participation was 2.6 years and the most common theatres of war were the Western Front (74%) and then the Middle East (Egypt, Sinai and Palestine) at 22%.

View Tables 1–4, Figure 1.

Morbidity burden

The great majority (94%) of this study population had at least one non-fatal new condition diagnosed and 89% had at least one hospitalisation for a new condition (Table 2). Indeed, the average participant had 2.4 new diagnoses and 1.8 hospitalisations for new conditions during their military service. This equated to 0.9 new conditions and 0.7 hospitalisations for new conditions per year of military service.

In terms of specific conditions, 42% of the personnel experienced at least one conflict-associated injury event (Table 3; Figure 1). Injuries from chemical warfare (gas poisoning) were experienced by 6% of personnel. But most of the new diagnoses were for infectious diseases, followed by the grouping of “other causes” (e.g., mental health) and then conflict-related injuries (117, 74 and 50 cases per 100 personnel respectively).

Respiratory conditions (including influenza, pneumonia, bronchitis and tuberculosis) alone impacted around a third of personnel (33%), with influenza being diagnosed in 19%. Sexually transmitted infections affected 14% of personnel (16 cases per 100 personnel), with gonorrhoea being the most common specified type.

Diseases typically reflecting hazardous environmental conditions were relatively common e.g., for dysentery/gastroenteritis at 12% and scabies at 5% of personnel. Less common were “trench” diseases (i.e., trench fever, trench foot, trench mouth), and there were no identified cases of typhoid and typhus.

Diagnoses suggestive of post-traumatic stress disorder (PTSD) were present in 10% of the personnel (9.5 cases per 100 personnel). The most common term used was “disordered action of the heart” (DAH), followed by neurasthenia and shell shock.

Due to either injuries or illnesses, most of the personnel were deemed “unfit for military service” by a military medical board (59%) at some point in their military service (Table 3).

Associations between morbidity and lifespan

The comparisons in Table 4 suggest no statistically significant differences between the various groups. Nevertheless, the pattern was for slightly lower lifespan among those with more diagnosed new conditions, more hospitalisations for new conditions, having had a STI diagnosis and being declared unfit at some point. The exception was for having a mental health diagnosis, which was associated with a slightly higher lifespan (albeit also not statistically significant).

Discussion

Main findings and interpretation

The major finding of this work was the very high morbidity burden of this military force—with 94% having at least one new condition diagnosed. The high level of personnel hospitalised (89%) also attests to the relative severity of most conditions, as does the majority (59%) of personnel being deemed no longer fit for further military service at some stage. These high proportions contrast with the official number of personnel wounded or suffering illness as detailed in the Introduction (41,317 personnel, equivalent to 39% of all NZEF personnel).

However, our estimate for diagnosed conditions will still be an under-estimate as it will not have captured more minor conditions. For example, nearly all of these personnel probably had a lice infestation[[35]] and many would have had symptomatic influenza during the pandemic in 1918–1919[[22]] without it necessarily being recorded in the military files. We also did not count as hospitalisations the admissions to field ambulance units or casualty clearing stations, some of which were for several days, if the soldier returned to the unit.

That infectious disease diagnoses were over twice as common as conflict-related injuries (117 vs 50 cases per 100 personnel respectively) is in contrast to the mortality burden for the NZEF in this war. That is, direct conflict-related deaths were 89% of all deaths compared to 8% dying of “disease”.[[18]] But in the preceding war involving New Zealand military personnel (the South African War), 59% of deaths were from disease.[[13]]

Condition severity was sometimes such that injuries were likely to have resulted in life-long disabilities (e.g., for head injuries and amputations). One of the personnel in this study had severe facial injuries that was officially deemed a factor in his suicide soon after the war. Some of the various infectious diseases listed in Table 3 could also result in adverse long-term sequalae e.g., tuberculosis, syphilis and malaria. Fortunately, there were no cases of typhoid identified in this sample, possibly a reflection of most of these personnel being vaccinated against it. Similarly, there were no cases of typhus, which was a major cause of death in Eastern Europe during this war.[[7]]

The overall cumulative incidence of STIs in this study (16 cases per 100 personnel) was fairly similar to that estimated previously by an Australian medical historian: at 130 per 1,000 for New Zealand personnel vs 158 per 1,000 for Australian personnel.[[35]] Further work is needed to estimate if such differences by country related to efforts by New Zealand military leadership in STI control, along with the advocacy efforts of Ettie Rout,[[42]] which contributed to condom distribution from late 1917.

The finding of 10% of personnel being given a likely PTSD diagnosis is also probably an under-estimate, given how this condition was poorly understood at the time.[[29]] Indeed, a study of Vietnam War veterans in New Zealand reported that 20% had PTSD.[[43]] A more recent study of serving and retired New Zealand military personnel identified 30% with scores indicative of post-traumatic stress.[[44]]

None of the lifespan results in this study provide statistical evidence of a link with morbidity experiences during the war. But the results were generally in the direction of such an association and so larger studies could consider exploring these issues further. An Australian study of WWI veterans did find statistically significant increased mortality after 1921 for those who were: discharged as medically unfit, discharged as partially/totally permanently disabled and being discharged due to “venereal disease”.[[45]]

Study strengths and limitations

A strength of this study is that it is the first relatively in-depth analysis of morbidity in a random sample of New Zealand military participants of WWI (to our knowledge). The research benefitted from the individual military records being available online and from the researchers having extensive experience (from previous studies) in interpreting the archival military records of the NZEF, knowledge of the WWI military environment and knowledge of medical terminology. Nevertheless, various limitations with our study need to be considered. In particular:

• Despite involving random sampling, the study sample was only “fairly representative” of all military personnel in the NZEF given various exclusions. These exclusions are detailed further in the Appendix, but the major ones involved not going overseas to fight, being female, being Pasifika, and not surviving the war. As such it does not reflect the morbidity experience of these particular groups (and indeed, those killed in the war could also have had a worse morbidity profile in the period up until their deaths than other participants).

• We could not account for conditions not detailed in the military files. This under-recording was probably common, especially for more minor conditions that did not involve treatment by medical personnel (e.g., lice infestation and milder cases of pandemic influenza as discussed above). Indeed, one New Zealand soldier contributed a satirical poem to the “Chronicles of the N.Z.E.F” about the how wounded men were entitled to wear a gold stripe on the left sleeve, yet there was no formal recognition for “little ills” like “dysent’ry”, fever, septic sores, shell shock, frost-bite, rotting feet and being gassed.[[46]] Also, some conditions may not have been self-reported (e.g., symptoms of a STI) given the punitive approaches that could be taken by the military authorities.[[25]] Similarly, such “sensitive” diagnoses relating to STIs or mental health may have not been recorded by staff on purpose, so as to protect the reputation and future career of the patient. Finally, dental records were relatively sparse in the individual military files, suggestive that such records were held separately.

• There was a lack of specificity to some of the conditions as shown by the “pyrexia of unknown origin” category in Table 3. Such fever symptoms could have potentially arisen from many different infectious diseases.

• We may have missed some relevant data due to misinterpreting the hand-written text/acronyms/abbreviations in the archival military files. This is because of the highly cursive handwriting styles typically used and due to the complexity of some of the records (e.g., one was 189 pages long, and some were mixed up with WWII records). Nevertheless, the inter-observer assessment study suggested reasonable results for sensitivity and specificity to the extent these can be estimated. Indeed, the values (such as 84% for the lowest end of the sensitivity range) might be under-estimates since the first author also did subsequent logic checks on the entire dataset and identified additional data items that could then be included in the final dataset version.

Possible lessons for governments and further research possibilities

It has taken over 100 years for the morbidity burden for WWI personnel to be established in terms of new conditions and hospitalisations for new conditions. This highlights the need for governments to properly document such health burdens from past wars. Such documentation could better inform the need for conflict prevention (e.g., via diplomacy) as well as for ongoing maintenance of high health status among serving military personnel, provisioning them with appropriate equipment and ensuring high-quality medical services to protect and treat them.

Further research could be done, including studies that explore the relationship between health conditions and the proximity to frontline combat in various theatres of WWI. Similarly for health risks associated with different roles in the military (e.g., being a health worker, being a private or officer, etc.) and for cross-country comparisons (e.g., New Zealand vs Australian military personnel). Māori or Pasifika researchers could also be funded to study the health burden in a random sample of these ethnic groups of military personnel.

Conclusions

The overall morbidity burden of this military force in WWI was very high, and much higher than the previous official estimates. A wide range of conditions were found in this study, but as with preceding conflicts the cases of infectious diseases were more frequent than those from conflict-related injuries.

View Appendix.

Summary

Abstract

Aim

Studies of the morbidity burden of military personnel participating in the First World War (WWI) have tended to focus on specific outcomes (e.g., injuries). Therefore, we aimed for a more complete assessment.

Method

From a random sample of active war service-exposed New Zealand WWI veterans used in previously published work, we examined a random subsample of 200 personnel. Data on diagnoses, hospitalisations and outcomes were extracted from the online archival military files.

Results

These personnel experienced a very high morbidity burden with 94% having at least one new condition diagnosed during their military service (mean: 2.4 per individual; range: 0 to 8). The relative severity of these conditions was reflected by the high level of hospitalisation (89% at least once; mean: 1.8 hospitalisations for new conditions per individual) and 59% of personnel being deemed no longer fit for military service at some stage. More of the new diagnoses were for infectious diseases than for conflict-related injuries (117 vs 50 cases per 100 personnel).  Respiratory conditions such as influenza, pneumonia and tuberculosis affected 33% of personnel, and 14% were diagnosed with sexually transmitted infections. Diseases reflecting hazardous environmental conditions were relatively common e.g., for dysentery/gastroenteritis in 12% and scabies in 5% of personnel. Diagnoses suggestive of post-traumatic stress disorder (PTSD) were present in 10% and chemical warfare injuries in 6%.

Conclusion

The overall morbidity burden of this military force in WWI was very high, and much higher than the previous official estimates.

Author Information

Nick Wilson: Department of Public Health, University of Otago Wellington, New Zealand. Jennifer A Summers: Department of Public Health, University of Otago Wellington, New Zealand. Glyn Harper: Massey University, Palmerston North, New Zealand. George Thomson: Department of Public Health, University of Otago Wellington, New Zealand.

Acknowledgements

The authors thank Christine Clement (genealogist) for assistance with determining the dates of birth and death for this cohort. Auckland War Memorial Museum kindly provided a copy of the Cenotaph records that assisted with sampling.

Correspondence

Professor Nick Wilson: Department of Public Health, University of Otago Wellington, Mein St, Newtown, Wellington, New Zealand.

Correspondence Email

nick.wilson@otago.ac.nz

Competing Interests

None declared.

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The First World War (WWI; 1914 to 1918) caused a substantial burden of injury and disease among participating military personnel. The most common injuries were caused by weapons (e.g., shrapnel from artillery, bullets and grenades). These injuries ranged from minor wounds up to those requiring limb amputations and causing permanent disability (e.g., blindness, deafness and traumatic brain injury).

Reviews have covered other health conditions in these personnel, including: the effects of the 1918 influenza pandemic on United States (US) and other soldiers;[[1,2]] the occurrence of malaria;[[3]] the (re)emergence of trench fever;[[4]] trench foot and other trench diseases;[[5,6]] and infectious diseases.[[7]] Reviews of mental health impacts have included the psychological effects on medical personnel involved,[[8]] shell shock and other psychoneuroses.[[9,10]]

For New Zealand, there were an estimated 98,950 military personnel who served overseas in WWI, and 7,036 who served on home territory in the New Zealand Expeditionary Force (NZEF) for a total of 105,986.[[11]] An estimated 18.2% died during the war and up to the end of 1923 (with this period used in the official New Zealand Roll of Honour[[11]]). The official number of personnel wounded or suffering illness was 41,317 (equivalent to 39.0% of NZEF personnel). However, this number included “all those removed from the front-line for medical treatment”, as well as including repeat hospitalisations of soldiers, so it was more “than the number of ‘wounded men’ per se”.[[11]]

These estimates do not include the more than 12,000 New Zealanders who served separately with other military forces during this war.[[12]] We also suspected that the official number of those wounded or suffering illness would be far below the level of overall morbidity that could be found upon examining military records for individual personnel—as found in a study of New Zealand personnel who served overseas in the South African War.[[13]]

The New Zealand military personnel were predominantly volunteers, though 26.0% were conscripted.[[14]] Previous studies of this military population have focussed on their overall lifespan,[[15–17]] but also aspects of their injury burden.[[18,19]] The infectious disease burden included that from pandemic influenza,[[20–23]] dysentery,[[24]] sexually transmitted infections[[25]] and disease outbreaks in training camps.[[26]] Other health aspects studied include the poor nutrition (e.g., at Gallipoli),[[27]] oral health[[28]] and mental health.[[29,30]] A wide range of health conditions were described in an official report published soon after the war[[31]] and a book details the medical services for the NZEF.[[32]] Other works cover a range of different health conditions.[[33–36]]

There is evidence of persisting disabilities after the war from the war pension data for New Zealand. As of 31 March 1921, a total of 40,227 veterans had lodged claims for war pensions for war-related disability and 17,612 dependents had also lodged war pension claims (for the period September 1915 to 1921).[[37]] Of all these claimants, 51,711 (or 89% of the total of 57,839) were granted war pensions (with this proportion not given separately for veterans vs dependents). Studies have also indicated elevated post-war morbidity in the veteran population. A cohort study following returned NZEF personnel across their remaining lifetimes found that 1.7% committed suicide.[[38]] Those who had been wounded, sick or medically discharged were found to have a significantly higher chance of suicide. Another study reported elevated suicide rates among these veterans compared to civilian men in the same age cohort during the 1920s and subsequent decades.[[39]] Other work has found death certificates of veterans that are suggestive of post-war deaths from suicide and alcoholism that could have been war related, along with deaths associated with operations on wounds and “war disability”.[[15]]

But despite all this work, it remains unclear what the overall injury/disease burden was for the New Zealand military personnel in this war. Similarly, for detail on the seriousness of the conditions e.g., as determined by hospitalisation. We therefore aimed to assess this burden with an in-depth examination of a random selection of military personnel from a national military force: that for Aotearoa New Zealand.

By way of further background, the NZEF mainly fought in Europe on the Western Front, but was also part of campaigns in the Middle East (Gallipoli and Palestine).[[40]] After its experience of fierce fighting at Gallipoli (1915), the newly formed New Zealand Division was sent to the Western Front in early 1916. It was initially assigned to a relatively quiet sector of the front at Armentières. This was to allow the troops to acclimatise and to familiarise themselves with the new warfare conditions on the Western Front. Following this, they were then dispatched to significant sectors of the Western Front, participating in major battles such as those at the Somme (1916), Messines (1917), Passchendaele (1917), the German Spring Offensive (1918) and the Hundred Days final offensive. These were among the most intense and pivotal campaigns of WWI. The last military action on the Western Front for the New Zealanders was the liberation of the town of Le Quesnoy (where the New Zealand Liberation Museum will be opened in October 2023). A map showing relevant areas for the New Zealand military on the Western Front is available here: https://nzhistory.govt.nz/media/photo/western-front-1916-17-map.

Methods

Sample selection

The sample was derived from a previous study on a random sample of NZEF participants in WWI.[[17]] From this larger sample we randomly selected 200 personnel for the in-depth analysis of their morbidity experience (for further details see the Appendix).

Data collection

All the socio-demographic data (including ethnicity and occupational class) were collected, as per the previously published study,[[17]] as were military rank and participation in previous and subsequent wars. Added to this were data on new diagnoses, hospitalisations for new conditions and discharges from the military on medical grounds (all from the online archive of military files[[41]]). These files were almost all hand-written, often in difficult conditions at battalion or similar level.

On occasions, the paucity of details in the military files on health conditions required some assumptions, as follows:

• Where a condition could plausibly have been related to subsequent relapses or sequelae, we did not count these sequelae conditions separately. For example, a reference to “debility” that was followed several months after “influenza” or “dysentery” was assumed to be sequelae of one of these earlier diagnoses.

• For hospitalisations, we also distinguished between those for new conditions as opposed to those related to transfers to other facilities (e.g., from hospital to convalescent facility) or ongoing treatment for a previously identified condition. We collected data on all admissions to hospitals, hospital ships and convalescent care facilities, but did not count visits to field ambulance units or casualty clearing stations that did not result in hospitalisation. To facilitate the data collection process, a detailed list of terms and acronyms used in the military files was compiled beforehand (see the Appendix).

• Where a particular diagnosis was first made after military service was completed e.g., a diagnosis of “shell shock” by a medical board after the war, we assumed that this condition had commenced while still in military service.

• The timing of “frontline” status was established by military file entries such as: “joined battalion” or battery or similar frontline unit (typically after periods in training or in the “rear”).

Other data sources that were occasionally consulted were online obituaries (e.g., in the dataset: Papers Past [https://paperspast.natlib.govt.nz/]).

Inter-observer reliability assessment for data collection

As the data extraction was first done by a single author, two other authors with experience in work with NZEF records each independently re-examined 10 randomly selected additional files each (to make up a 10% sample). The assessment compared the new diagnoses, the new hospitalisations and samples of extracted numerical data.

Data analysis

Data were collated in a Microsoft Excel file and univariate analyses were conducted using EpiInfo v7.1.5.2. Lifespan comparisons for different groups used analysis of variance (ANOVA).

Ethics statement

Ethical approval for this study was provided through the University of Otago Human Ethics Committee process (Category B Approval, D22/030).

Results

Inter-observer reliability assessment

Based on the two subsequent observers independently examining a 10% sample of the data, the following sensitivity estimates were obtained for the first and main observer (when the “true” denominator is assumed to be that from all observers combined): 89% (41/46) for the number of new conditions; 91% (39/43) for the number of hospitalisations for new conditions; 84% (21/25) for the number of war theatres; 100% (19/19) for the correct date of death (when available from this source); and 100% (20/20) for length of stay overseas. Errors were made by the main observer for an incorrect “unfit status” (5%, 1/19) and for one diagnosis (2%, 1/46, where the words disability and diabetes were confused with each other).

Characteristics of the studied population

The average age of this randomly selected sample was 25.4 years (at the start of the war) and they were nearly all of European ethnicity (i.e., only 2.5% were Māori) (Table 1). The occupational class was dominated by the lower three groupings (54%) and military rank was predominantly in the lowest rankings (88%). By the end of 1916, 48% had been to a frontline position, and by the end of the war, 91.5%. The mean length of war participation was 2.6 years and the most common theatres of war were the Western Front (74%) and then the Middle East (Egypt, Sinai and Palestine) at 22%.

View Tables 1–4, Figure 1.

Morbidity burden

The great majority (94%) of this study population had at least one non-fatal new condition diagnosed and 89% had at least one hospitalisation for a new condition (Table 2). Indeed, the average participant had 2.4 new diagnoses and 1.8 hospitalisations for new conditions during their military service. This equated to 0.9 new conditions and 0.7 hospitalisations for new conditions per year of military service.

In terms of specific conditions, 42% of the personnel experienced at least one conflict-associated injury event (Table 3; Figure 1). Injuries from chemical warfare (gas poisoning) were experienced by 6% of personnel. But most of the new diagnoses were for infectious diseases, followed by the grouping of “other causes” (e.g., mental health) and then conflict-related injuries (117, 74 and 50 cases per 100 personnel respectively).

Respiratory conditions (including influenza, pneumonia, bronchitis and tuberculosis) alone impacted around a third of personnel (33%), with influenza being diagnosed in 19%. Sexually transmitted infections affected 14% of personnel (16 cases per 100 personnel), with gonorrhoea being the most common specified type.

Diseases typically reflecting hazardous environmental conditions were relatively common e.g., for dysentery/gastroenteritis at 12% and scabies at 5% of personnel. Less common were “trench” diseases (i.e., trench fever, trench foot, trench mouth), and there were no identified cases of typhoid and typhus.

Diagnoses suggestive of post-traumatic stress disorder (PTSD) were present in 10% of the personnel (9.5 cases per 100 personnel). The most common term used was “disordered action of the heart” (DAH), followed by neurasthenia and shell shock.

Due to either injuries or illnesses, most of the personnel were deemed “unfit for military service” by a military medical board (59%) at some point in their military service (Table 3).

Associations between morbidity and lifespan

The comparisons in Table 4 suggest no statistically significant differences between the various groups. Nevertheless, the pattern was for slightly lower lifespan among those with more diagnosed new conditions, more hospitalisations for new conditions, having had a STI diagnosis and being declared unfit at some point. The exception was for having a mental health diagnosis, which was associated with a slightly higher lifespan (albeit also not statistically significant).

Discussion

Main findings and interpretation

The major finding of this work was the very high morbidity burden of this military force—with 94% having at least one new condition diagnosed. The high level of personnel hospitalised (89%) also attests to the relative severity of most conditions, as does the majority (59%) of personnel being deemed no longer fit for further military service at some stage. These high proportions contrast with the official number of personnel wounded or suffering illness as detailed in the Introduction (41,317 personnel, equivalent to 39% of all NZEF personnel).

However, our estimate for diagnosed conditions will still be an under-estimate as it will not have captured more minor conditions. For example, nearly all of these personnel probably had a lice infestation[[35]] and many would have had symptomatic influenza during the pandemic in 1918–1919[[22]] without it necessarily being recorded in the military files. We also did not count as hospitalisations the admissions to field ambulance units or casualty clearing stations, some of which were for several days, if the soldier returned to the unit.

That infectious disease diagnoses were over twice as common as conflict-related injuries (117 vs 50 cases per 100 personnel respectively) is in contrast to the mortality burden for the NZEF in this war. That is, direct conflict-related deaths were 89% of all deaths compared to 8% dying of “disease”.[[18]] But in the preceding war involving New Zealand military personnel (the South African War), 59% of deaths were from disease.[[13]]

Condition severity was sometimes such that injuries were likely to have resulted in life-long disabilities (e.g., for head injuries and amputations). One of the personnel in this study had severe facial injuries that was officially deemed a factor in his suicide soon after the war. Some of the various infectious diseases listed in Table 3 could also result in adverse long-term sequalae e.g., tuberculosis, syphilis and malaria. Fortunately, there were no cases of typhoid identified in this sample, possibly a reflection of most of these personnel being vaccinated against it. Similarly, there were no cases of typhus, which was a major cause of death in Eastern Europe during this war.[[7]]

The overall cumulative incidence of STIs in this study (16 cases per 100 personnel) was fairly similar to that estimated previously by an Australian medical historian: at 130 per 1,000 for New Zealand personnel vs 158 per 1,000 for Australian personnel.[[35]] Further work is needed to estimate if such differences by country related to efforts by New Zealand military leadership in STI control, along with the advocacy efforts of Ettie Rout,[[42]] which contributed to condom distribution from late 1917.

The finding of 10% of personnel being given a likely PTSD diagnosis is also probably an under-estimate, given how this condition was poorly understood at the time.[[29]] Indeed, a study of Vietnam War veterans in New Zealand reported that 20% had PTSD.[[43]] A more recent study of serving and retired New Zealand military personnel identified 30% with scores indicative of post-traumatic stress.[[44]]

None of the lifespan results in this study provide statistical evidence of a link with morbidity experiences during the war. But the results were generally in the direction of such an association and so larger studies could consider exploring these issues further. An Australian study of WWI veterans did find statistically significant increased mortality after 1921 for those who were: discharged as medically unfit, discharged as partially/totally permanently disabled and being discharged due to “venereal disease”.[[45]]

Study strengths and limitations

A strength of this study is that it is the first relatively in-depth analysis of morbidity in a random sample of New Zealand military participants of WWI (to our knowledge). The research benefitted from the individual military records being available online and from the researchers having extensive experience (from previous studies) in interpreting the archival military records of the NZEF, knowledge of the WWI military environment and knowledge of medical terminology. Nevertheless, various limitations with our study need to be considered. In particular:

• Despite involving random sampling, the study sample was only “fairly representative” of all military personnel in the NZEF given various exclusions. These exclusions are detailed further in the Appendix, but the major ones involved not going overseas to fight, being female, being Pasifika, and not surviving the war. As such it does not reflect the morbidity experience of these particular groups (and indeed, those killed in the war could also have had a worse morbidity profile in the period up until their deaths than other participants).

• We could not account for conditions not detailed in the military files. This under-recording was probably common, especially for more minor conditions that did not involve treatment by medical personnel (e.g., lice infestation and milder cases of pandemic influenza as discussed above). Indeed, one New Zealand soldier contributed a satirical poem to the “Chronicles of the N.Z.E.F” about the how wounded men were entitled to wear a gold stripe on the left sleeve, yet there was no formal recognition for “little ills” like “dysent’ry”, fever, septic sores, shell shock, frost-bite, rotting feet and being gassed.[[46]] Also, some conditions may not have been self-reported (e.g., symptoms of a STI) given the punitive approaches that could be taken by the military authorities.[[25]] Similarly, such “sensitive” diagnoses relating to STIs or mental health may have not been recorded by staff on purpose, so as to protect the reputation and future career of the patient. Finally, dental records were relatively sparse in the individual military files, suggestive that such records were held separately.

• There was a lack of specificity to some of the conditions as shown by the “pyrexia of unknown origin” category in Table 3. Such fever symptoms could have potentially arisen from many different infectious diseases.

• We may have missed some relevant data due to misinterpreting the hand-written text/acronyms/abbreviations in the archival military files. This is because of the highly cursive handwriting styles typically used and due to the complexity of some of the records (e.g., one was 189 pages long, and some were mixed up with WWII records). Nevertheless, the inter-observer assessment study suggested reasonable results for sensitivity and specificity to the extent these can be estimated. Indeed, the values (such as 84% for the lowest end of the sensitivity range) might be under-estimates since the first author also did subsequent logic checks on the entire dataset and identified additional data items that could then be included in the final dataset version.

Possible lessons for governments and further research possibilities

It has taken over 100 years for the morbidity burden for WWI personnel to be established in terms of new conditions and hospitalisations for new conditions. This highlights the need for governments to properly document such health burdens from past wars. Such documentation could better inform the need for conflict prevention (e.g., via diplomacy) as well as for ongoing maintenance of high health status among serving military personnel, provisioning them with appropriate equipment and ensuring high-quality medical services to protect and treat them.

Further research could be done, including studies that explore the relationship between health conditions and the proximity to frontline combat in various theatres of WWI. Similarly for health risks associated with different roles in the military (e.g., being a health worker, being a private or officer, etc.) and for cross-country comparisons (e.g., New Zealand vs Australian military personnel). Māori or Pasifika researchers could also be funded to study the health burden in a random sample of these ethnic groups of military personnel.

Conclusions

The overall morbidity burden of this military force in WWI was very high, and much higher than the previous official estimates. A wide range of conditions were found in this study, but as with preceding conflicts the cases of infectious diseases were more frequent than those from conflict-related injuries.

View Appendix.

Summary

Abstract

Aim

Studies of the morbidity burden of military personnel participating in the First World War (WWI) have tended to focus on specific outcomes (e.g., injuries). Therefore, we aimed for a more complete assessment.

Method

From a random sample of active war service-exposed New Zealand WWI veterans used in previously published work, we examined a random subsample of 200 personnel. Data on diagnoses, hospitalisations and outcomes were extracted from the online archival military files.

Results

These personnel experienced a very high morbidity burden with 94% having at least one new condition diagnosed during their military service (mean: 2.4 per individual; range: 0 to 8). The relative severity of these conditions was reflected by the high level of hospitalisation (89% at least once; mean: 1.8 hospitalisations for new conditions per individual) and 59% of personnel being deemed no longer fit for military service at some stage. More of the new diagnoses were for infectious diseases than for conflict-related injuries (117 vs 50 cases per 100 personnel).  Respiratory conditions such as influenza, pneumonia and tuberculosis affected 33% of personnel, and 14% were diagnosed with sexually transmitted infections. Diseases reflecting hazardous environmental conditions were relatively common e.g., for dysentery/gastroenteritis in 12% and scabies in 5% of personnel. Diagnoses suggestive of post-traumatic stress disorder (PTSD) were present in 10% and chemical warfare injuries in 6%.

Conclusion

The overall morbidity burden of this military force in WWI was very high, and much higher than the previous official estimates.

Author Information

Nick Wilson: Department of Public Health, University of Otago Wellington, New Zealand. Jennifer A Summers: Department of Public Health, University of Otago Wellington, New Zealand. Glyn Harper: Massey University, Palmerston North, New Zealand. George Thomson: Department of Public Health, University of Otago Wellington, New Zealand.

Acknowledgements

The authors thank Christine Clement (genealogist) for assistance with determining the dates of birth and death for this cohort. Auckland War Memorial Museum kindly provided a copy of the Cenotaph records that assisted with sampling.

Correspondence

Professor Nick Wilson: Department of Public Health, University of Otago Wellington, Mein St, Newtown, Wellington, New Zealand.

Correspondence Email

nick.wilson@otago.ac.nz

Competing Interests

None declared.

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