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| Journal of the New Zealand Medical Association,
09-March-2012, Vol 125 No 1351
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Skin infections in children in a New Zealand primary
care setting: exploring beneath the tip of the iceberg
Cathryn O’Sullivan, Michael G Baker
Skin infections are a common complaint in primary care and
are usually considered benign. However, in both New Zealand (NZ) and
international settings, these infections are becoming an increasingly
significant source of childhood morbidity, with the rate of skin infections
requiring hospitalisation (termed ‘serious skin infections’)
steadily increasing during the last two
decades.1–7
In NZ, the rate of serious skin infections, doubled between
1990 and 2007.4 In 2004, a report by Hunt found
the national rate of cellulitis in children was twice that of Australia and the
United States of America.8
Recent analyses have found that serious skin infections
contribute heavily to health inequalities with the greatest hospitalisation
rates observed in Māori and Pacific
children.4,5,8–11 These trends are
hypothesised to reflect corresponding patterns of disease in the
community,8 however there are no published
studies examining skin infections in the NZ primary care setting, where many
patients initially present and the major burden of illness is managed. This
deficit is likely due to the lack of routine primary care level surveillance for
most health conditions in NZ.
Hospital admissions for serious skin infections represent
the ‘tip of the iceberg’ in relation to the wider community burden
of disease.4,8 We aimed to estimate the
incidence of skin infection cases in primary care in children in the Tairawhiti
(Gisborne) region, describe the basic epidemiology of these infections, and
compare these characteristics with serious skin infections hospitalised in the
region during the same period.
MethodsWe conducted a prospective observational analysis of
skin infection cases in children seen by a cohort of general practitioners (GPs)
in the Tairawhiti region.
Study location—The Tairawhiti
region is a relatively isolated area of 45,000 people on the East Coast of
NZ’s North Island. The region is unique for its large Māori
population (47.3% of the total population and 58.4% of the 0–14 year old
population), young age distribution (26.2% of people are aged less than 15
years),12 and high levels of deprivation (the
Gisborne region has the highest proportion of the most deprived residents in the
country).13
In Tairawhiti, childhood skin infections present a
major challenge to both primary and secondary health services. The
region’s serious skin infection incidence is not only the highest in
NZ,4 research presented in companion articles
in this issue of the New Zealand Medical Journal has shown it is
considerably greater than that expected, even after standardising for the
high-risk age, ethnicity and deprivation population composition.
General practitioner recruitment and data
collection—The raw data for this study were collected by
prospective consultation coding by a group of Tairawhiti GPs. All GPs within the
region were approached and their voluntary participation in this study sought.
Out of the usual local GP population of approximately 20 full-time equivalent
practitioners working in six primary practices, nine GPs from three different
practices agreed to participate. During the study period, 4627 of the 18,456
(25.1%) 0–14 year olds usually resident population of the Tairawhiti
region were registered in the practice populations of these GPs.
Over the 10-week period, 19 May 2008 to 28 July 2008,
GPs coded all incident cases of skin infection in children using the READ code
system. Similar to International Classification of Disease (ICD) codes used in
hospitals, READ codes are a standardised and hierarchically-arranged clinical
terminology system widely used in primary care practices for coding diagnoses as
well as a range of patient demographic and clinical
data.14
All skin infections were included regardless of whether
they were the primary reason for presentation or a secondary diagnosis. Repeat
visits for the same episode of infection were not coded. All visits were during
routine office hours of 8am to 5pm, Monday to Friday. A minimum level code of
‘M0.00’ (Skin/subcutaneous tissue infections) was recorded in the
computerised clinical records of appropriate patients using
MedTech32®,
the electronic patient management system used in all participating
practices.
Email reminders were sent to GPs every 3–4 weeks
during the data collection phase. At the end of this period, the Query
Builder® function of
MedTech32® was used to design and run a
standardised data query. An arbitrary and anonymous unique identifier was
assigned to each case and raw data variables including READ code and free-text
diagnosis description, date of birth, gender and ethnicity (Māori vs.
non-Māori) were extracted and collated centrally.
Case definition—Cases of skin
infection were diagnosed clinically based on the experience of participating
GPs, however a written case definition was provided to standardise inclusion
criteria:
“Any child aged
0–14 years old, seen by a participating GP during the study period, with
clinical evidence of a new episode of active bacterial infection of the skin or
subcutaneous tissue including any of the following diagnoses: cellulitis,
erysipelas, impetigo, subcutaneous abscess, furuncle, carbuncle, acute
lymphadenitis, any pyoderma including bacterial super-infection of
eczema/scabies/chickenpox/insect bites, and any other infection of the skin or
subcutaneous tissue.”
Hospital cases—We used
anonymised hospitalisation data provided by the New Zealand Ministry of Health
to identify all cases of serious skin infection in children aged 0–14
years admitted to Gisborne Hospital over the same 10-week period specified
above. The case definition of hospitalised serious skin infection utilised in
this study was developed in earlier work by the authors and has been described
in detail elsewhere.15 Cases were assigned an
arbitrary and anonymous unique identifier and the same basic demographic
variables as those collated for GP cases were extracted.
Data analysis—Age and
ethnicity-specific skin infection rates from participating GP registers were
directly standardised to the regional population to give an estimate of the
total number and rate of skin infection cases seen in children in primary care
in the Tairawhiti region. Confidence intervals (CIs) were constructed using the
methods of Clayton and Hills.16
Denominators in rate calculations were based on usually
resident population counts from the 2006 Census.
Annual infection rates were calculated from
extrapolations of observed data. Seasonal adjustment was not made as recent work
has shown there is very little seasonality in hospitalisation rates for skin
infections in the Tairawhiti region compared to NZ (see companion articles in
this issue of the New Zealand Medical Journal) and it is unknown
whether rates of skin infections in primary care exhibit seasonal trends.
The ethnicity and gender distribution of children in
general practice and in the hospital setting were compared using the
Fisher’s exact test. Age distributions were compared using the Mann
Whitney U test. A two-tailed p-value of less than 0.05 was considered
statistically significant.
Regional Ethics Committee approval was obtained for
this study.
ResultsIncidence and characteristics of skin infection
cases in primary care—Over the 10-week data collection period,
110 incident cases of skin infections in 107 children were recorded by the nine
participating GPs. Table 1 summarises the observed number and rate of cases in
each age and ethnicity group.
Based on age and ethnicity standardisation of observed
rates, there were an estimated 378.6 (95%CI: 312.4–458.9) cases of skin
infections seen in primary care, equivalent to a rate of 20.5 cases (95%CI: 16.9
to 24.9) per 1000 0–14-year-old children in the Tairawhiti region during
the 10-week study period (see Table 1).
Extrapolating these data longitudinally, without taking
seasonal adjustment into account, there were an estimated 1968.7 (95%CI:
1624.5–2386.3) cases of skin infections in children in the Tairawhiti
region primary care setting during 2008. This frequency is equivalent to an
annual incidence rate of 106.7 (95%CI: 85.2–127.2) per 1000 children in
the region, or 10.7% of the population if there were no repeat infections in the
same individuals.
In Māori children, there was a trend towards reducing
case incidence with increasing age. This trend was less apparent in
non-Māori children. Annual infection rates ranged from 29.0 per 1000 for
non-Māori children aged 10–14 years, up to 245.5 per 1000 for
Māori children aged 0–4 years.
Table 1. Skin infection incidence observed in
the study population, and estimated for the Tairawhiti region, 0–14 year
old children, May–July 2008
95% CI: 95% confidence interval; No.: number.
† Ethnicity and age-specific
rates of skin infections observed in participating primary care practices during
10-week study period.
‡ Based on usually resident
population data in 2006 Census.
§ Estimated number of primary
care cases of skin infection in children in the Tairawhiti region during the
10-week study period, based on multiplying the age and ethnicity specific rates
observed in participating GP practices by the Tairawhiti region population for
that age/ethnicity group.
# Estimated annual rate per 1000 of
primary care cases of skin infection in the Tairawhiti region, based on
annualising the 10-week rate (without seasonal adjustment).
Comparing skin infection cases seen in primary care
and hospital settings—During the same 10-week data collection
period, 27 cases of serious skin infection in 27 children were admitted to
Gisborne Hospital. Based on the estimated 378.6 primary care skin infection
cases in the region over this period, there were 14 primary care cases for every
one hospitalised serious skin infection.
Table 2 and Figure 1 summarise and compare the basic
demographic characteristics of primary care and hospital cases seen over the
same period in 2008. Most primary care cases were coded only to the minimum code
level of ‘M0.00’, so information on subtypes of skin infection and
free-text diagnosis description was not available.
There was a significant difference in the age distribution
of skin infection cases between the two settings (p=0.0041). Preschool-aged
children accounted for two-thirds (67%) of hospitalised cases of serious skin
infection but only 38% of infections in primary care. While just 15% of
hospitalised cases were in children aged 5–9 years, this group made up the
largest proportion of cases in primary care (41%). The 10–14 year old age
group accounted for the smallest proportion of cases overall.
Slightly more boys were admitted to hospital with a serious
skin infection than girls, 56% and 44% respectively, but this difference did not
reach statistical significance. There was no gender predominance in primary care
cases with equal numbers of male and female children suffering skin infections.
The difference between settings was not significant (p=0.67).
Just over three-quarters (77%) of skin infection cases in
the primary care setting were in Māori children. Hospitalised cases of
serious skin infections exhibited a similar ethnic distribution, with 78%
occurring in Māori children (p 1.00).
Table 2. Comparison of the demographic
characteristics of children with skin infections seen in primary care and
hospital settings in the Tairawhiti region, May–July 2008
No.: Number of cases.
PP:
Proportion of primary care cases.
PH:
Proportion of hospital cases.
PP
–
PH:
Difference between the primary care and hospital
proportions.
p: Two tailed p-value (>0.05
considered statistically significant).
Figure 1. Gender, age and ethnicity
distribution (%) of children with skin infections seen in primary care and
hospital settings in the Tairawhiti region, May–July 2008
 DiscussionSkin infections are a common childhood illness in NZ.
Results of this study suggest that 10.7% of children in the Tairawhiti region
consulted their GP with this complaint during 2008. The majority of infections
are adequately treated in the primary care setting, avoiding hospitalisation.
Population groups with the highest rates of infection were Māori children
and those in both the 0–4 and 5–9 year old age groups, with no
difference between male and female children.
We found that the epidemiology of skin infections in primary
care reflected that of hospitalised serious skin infections, except for the age
distribution of cases where there was a relatively higher proportion of
5–9 year olds presenting to primary care, whereas preschool-aged children
were more dominant among those hospitalised. (see articles entitled The
epidemiology of serious skin infections in New Zealand children: comparing the
Tairawhiti region with national trends, and Serious skin infections in
children a review of admissions to Gisborne Hospital (2006-2007) in this
issue of the New Zealand Medical Journal).
This study provides the first NZ estimate of the rate of
skin infection in children at the primary care level. Findings indicate that
during a 10-week period in 2008, there were 378.6 cases (95%CI:
312.4–458.9) of skin infections seen in primary care in the Tairawhiti
region, equivalent to an annual incidence rate of 106.7 cases per 1000 children
or one in every nine children in the region consulting their GP for a skin
infection during the 2008 year. This figure does not take into account repeat
presentations for the same episode of infection.
Over three-quarters of skin infections in primary care
occurred in Māori children with an almost identical proportion seen in
hospitalised cases. This similarity in ethnic distribution between the two
settings is important; it indicates that the high rates of serious skin
infections in Māori children reported in previous analyses of NZ
hospitalisation data4,5,8–11 are a
reflection of a similarly high burden of disease at the primary care level,
rather than ethnic disparities in hospital admission thresholds.
Māori experience higher rates of infectious diseases in
general.17 The reasons for this difference are
complex and multifactorial; they include household crowding, barriers to
accessing primary healthcare such as cost and longer travel distances, and a
range of socioeconomic
factors.17–22
The relatively even spread of primary care skin infection
cases across the 0–4 and 5–9 year old age groups was unexpected.
Previous analyses have found hospitalisation rates for serious skin infections
are highest in preschool-aged
children,4,5,8,9,23–26 and this
distribution has been thought to directly reflect community trends in infection
incidence. This finding could be an aberration due to our small sample size, but
alternative hypotheses could include lower admission thresholds in young
children or more severe disease requiring admission in a greater proportion of
such cases.
This is the first published study we are aware of that has
described the basic epidemiology of skin infections in children in a primary
care setting and made comparisons to equivalent data from hospitalised serious
skin infection cases over the same period. It is also the only study we know of
that has attempted to quantify the total primary care burden of childhood skin
infections within a region in NZ. However several limitations must be considered
in conjunction with its results.
Our analysis was based on a small number of primary care
cases recorded over a short time interval. Regional infection rates were
extrapolated from these observed data, and hence are subject to considerable
sampling error, reflected in wide confidence intervals. However, in comparison
to previous work estimating the primary care burden of skin infections, which
have solely comprised workforce surveys,8,27
this is an important step forward. The results are an indication of the
magnitude of the problem beyond frequently measured hospitalisation data, and
start to illuminate the area beneath the ‘tip of the iceberg’.
The generalisability of the findings to populations outside
the Tairawhiti region needs to be considered. If the ratio of 14 primary care
cases for every one hospitalised case applied uniformly across NZ, then the
4,453 hospitalisations observed annually
(2000–2007)4 would correspond to 62,347
GP cases per year. However, further studies in other primary care populations
are needed before relying on such extrapolations.
As involvement in this study was voluntary, it was not
feasible to have a randomly selected sample of local GPs participating.
Convenience sampling was therefore used. Potential clustering of practices
limited our ability to analyse certain census area unit-based demographic
variables, namely deprivation status. In addition, the analyses of the local
primary care burden of disease assume that the group of participating GPs are a
representative sample of all GPs in the Gisborne region and exhibited an average
hospital admission threshold similar to the population mean.
While this objective would be best guaranteed by
randomisation, we tried to minimise selection bias by including over one-quarter
of the usually resident 0–14 year old population of the Tairawhiti region
in the sample group, and ensuring participating GPs were recruited from a broad
range of practice sizes, types and locations. We were unable to obtain data to
compare the practice population demographics of GPs who participated and those
who did not.
There was a large difference between the expected number of
GP cases (based on GP-reported estimates made during preliminary discussions)
and the actual number of recorded cases. The facility to code patient diagnoses
exists within the computerised practice management systems used in almost all NZ
general practices. However, most consultations are not routinely assigned a
diagnostic code, so data collection in this study relied on participating GPs
manually entering READ codes. Hence, it is likely that low coding compliance
accounts for much of the discrepancy in expected and actual case numbers;
despite good intentions, a minimal level code for simplicity, and regular email
reminders, several participating GPs estimated their coding compliance was
approximately 50%. This bias will result in an underestimation of the primary
care burden of disease. However, it is also possible that some of the
discrepancy was because anecdotal case numbers were initially
overestimated.
GP cases were only recorded during routine office hours of
8am to 5pm, Monday to Friday. While there is an after-hours GP call-out service
available in Gisborne, high costs and direct access to the local emergency
department mean it is rarely utilised. As such, all cases presenting overnight
and during weekends were excluded from the dataset.
This study was not able to ascertain whether children
admitted to hospital with a serious skin infection were referred immediately by
their GP or after a failed trial of outpatient treatment. In addition, because
this was not a longitudinal study, we could not determine if the marked rise in
hospitalisation rates over the last two decades was due to comparative increases
in primary care case rates over this same period.
Further research is warranted to explore childhood skin
infections beneath the tip of the iceberg of serious hospitalised cases. While
infections seen by primary care providers do not comprise the whole community
burden of disease (infections may be self resolving or self treated), they do
account for a significant proportion.
Further work is needed to investigate whether the high
admission rates in NZ, compared to other developed countries, solely reflect
greater community rates of disease, or whether a larger proportion of skin
infections result in hospital admission.
Routine collection of primary care consultation data would
facilitate this endeavour, and eliminate many of the limitations described in
this study. One option would be to establish routine primary care surveillance
of skin infection in NZ. Such primary care surveillance is arguably one of the
largest gaps in NZ’s infectious disease surveillance
system.28
Many countries have well established general practice
sentinel systems that NZ could
emulate29–33 and NZ has successfully
piloted syndromic surveillance in the past for conditions including skin and
subcutaneous tissue infection.34
Competing interests: None
declared.
Author information: Cathryn
O’Sullivan, Masters of Medical Sciences Student; Michael G Baker,
Associate Professor; Department of Public Health, University of Otago,
Wellington
Acknowledgements: This work was supported
by initial funding from Tairawhiti District Health as part of a larger piece of
work made possible by a grant from the New Zealand Ministry of Health Reducing
Inequalities Budget.
The authors gratefully acknowledge the nine GPs who
participated in this study; for their willingness to be involved in this
research, and for the time spent coding during already busy consultations. The
authors also thank James Stanley who gave generously of his time and statistical
expertise; Dr Geoffrey Cramp who provided local project supervision; and the
staff of Turanganui PHO and Tairawhiti District Health Clinical Records for the
technical assistance they provided.
Correspondence: Associate Professor Michael
Baker, Department of Public Health, University of Otago, Wellington. PO Box
7343, Wellington South, New Zealand. Fax: +64 (0)4 3895319; email: michael.baker@otago.ac.nz
References:
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