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Caesarean section (CS) is one of the most common surgical procedures performed in hospitals. It is classified as a high-risk operation in the "clean" category. In New Zealand, as in other developed countries, the rate of CS has continued to rise, currently comprising over 25% of hospital births.1Surgical site infection (SSI) post-caesarean section increases maternal morbidity and costs and is thus an important problem. The benchmark SSI infection rate quoted in the RCOG green top guidelines is 6.4%;2 however, rates of SSI post CS vary widely in different publications due to differences in the criteria used to diagnose infection and varying lengths of follow-up postoperatively.3Risk factors contributing to SSI post CS are thought to include BMI, longer operation duration, age, blood loss, method of wound closure, and emergency procedures.3-6Methods This nested case-control study was conducted as a retrospective analysis using as a population all the caesarean sections for the 6 month period from 16 March 2009-15 September 2009 conducted at a single site—Waikato Hospital. Each of the patients identified in the study as having had a caesarean section was accompanied by a list of ICD9 codes. Patients with possible surgical site infections post-caesarean section were identified by manually searching through the obstetric notes of patients who had the electronic diagnostic codes "infection of obstetric surgical wound", "wound infection following a procedure", and "disruption of a caesarean section wound". CDC (US Center for Disease Control) criteria were then used to confirm infections in these cases. The case population with confirmed SSI was compared with two randomly selected (via random number generator) controls per case without SSI from the same wider 6-month population to identify any risk factors for SSI within the Waikato Hospital setting. Risk factors analysed include BMI, operation duration, age, blood loss, method of wound closure, use of prophylactic antibiotics, type of procedure, ethnicity, smoking, parity, duration of labour, and elapsed time since rupture of membranes (ROM), Statistical analysis—Categorical data were presented as frequency (percentage) and continuous data were presented as mean ± SD. Categorical variables were compared using a Chi-squared test or Fisher's exact test as appropriate. Continuous data were compared using the Kruskal-Wallis test. All P-values reported were two tailed and a P-value <0.05 was considered significant. A logistic regression of significant variables was also performed. The statistical programme SAS Version 9.1 was used for statistical analysis. Results This study identified 526 sections—192 elective lower segment caesarean sections, 331 emergency lower segment caesarean sections, and 3 emergency classical caesarean sections. In total, 25 of the 526 patients (5%) in the 6-month period analysed had a surgical site infection post-caesarean section. Of these, 15 were revealed during admission (3%), and the other 10 required hospital care post-discharge for treatment of infection (2%). The characteristics of the 25 cases and 50 controls are recorded in table 1. Table 1. Potential risk factors for post-caesarean section surgical site infection Variables Case (n=25) Control (n=50) P value Type of C-section, n (%) Emergency Elective 21 (84) 4 (16) 29 (58.0) 21 (42.0) 0.0243 Age, mean ± SD 27.2 ± 6.8 30.0 ± 6.2 0.0892 Ethnicity, n (%) Non-Maori Maori 18 (72) 7 (28) 37 (74) 13 (26.0) 1.0000 BMI (kg/m2), mean ± SD 34.7 ± 5.2 28.2 ± 6.1 0.0002 Smoking status, n (%) Smoker Non-smoker Unknown 6 (24) 13 (52) 6 (24) 19 (38) 27 (54) 4 (8) 0.4635 Parity, mean ± SD 0.7 ± 0.8 1.2 ± 1.4 0.0998 Duration of labours (hrs), mean ± SD 16.5 ± 7.6 9.5 ± 5.1 0.0019 Elapsed time since ROM (hrs), mean ± SD 17.4 ± 14.4 11.2 ± 5.1 0.2195 Operating time (mins), mean ± SD 46.8 ± 17.9 46.5 ± 13.2 0.5932 Type of closure, n (%) Sutures Staples Unknown 14 (56) 8 (32) 3 (12) 31 (62) 9 (18) 10 (20) 0.2417 Estimated blood loss (mL), mean ± SD 729 ± 475 632 ± 275 0.6044 Some data are missing for BMI, Smoking, Duration of labours, Elapsed time since ROM, type of closure, estimated blood loss. The key risk factors for surgical site infection post-caesarean section identified were elevated BMI, longer duration of labour, and having an emergency procedure. The mean BMI for the case group was 34.7kg/m2, as compared to 28.2kg/m2 in the control group (p=0.0002). Mean duration of labour in the case group was 16.5 hours, as compared to 9.5 hours in the control group (p=0.0019), and the percentage of the case group having an emergency procedure was 84%, versus 58% in the control group (p=0.0243) . Whilst cases were on average 3 years younger, had 100mls greater blood loss, and were 14% more likely to have had staples used for wound closure, these findings did not reach statistical significance. Antibiotic prophylaxis was used in all cases and controls A multivariate logistic regression was performed on the risk factors ‘type of procedure' and ‘BMI'. This regression analysis adjusted for age and BMI for the risk factor type of procedure; and adjusted for age, operating time, duration of labour, and type of procedure for the risk factor BMI. This analysis confirmed type of procedure and BMI as being independent risk factors for SSI, even after adjusting for other potentially confounding factors (see table 2). Table 2. Logistic regression of risk factors BMI and type of procedure Variables Case (n=25) Control (n=50) OR (95% CI) P value Emergency (vs elective) section, n(%) Emergency Elective Unadjusted Adjusted for age & BMI 21 (84) 4 (16) 29 (58.0) 21 (42.0) 3.80 (1.14-12.66) 4.22 (1.01-17.86) 0.0243 BMI (kg/m2), mean ± SD Unadjusted Adjusted for age Adjusted for age & operating time Adjusted for age & labour duration Adjusted for age & procedure type 34.7 ± 5.2 28.2 ± 6.1 1.21 (1.09-1.34) 1.20 (1.08-1.33) 1.20 (1.08-1.34) 1.31 (1.06-1.60) 1.22 (1.09-1.38) 0.0002 Discussion This retrospective analysis suggests that the rate of surgical site infection post-caesarean section in Waikato hospital was approximately 5% which is similar to the in-hospital rate found in other studies. However, this figure recognises only those patients requiring inpatient admission and treatment. Those who received outpatient (or no) treatment for their infection are unable to be captured by the methodology used. Thus, the total infection rate is likely to be higher than that identified in this study, as infections captured in an in-hospital setting may represent as little as one-third of the total number of infections.7 Significant risk factors for infection identified include elevated BMI, longer duration of labour, and having an emergency (as compared to an elective) procedure. The link between obesity and increased SSI risk is well established in the literature, and relates to increased subcutaneous tissue thickness (which is relatively avascular), impaired immune function, increased wound area, need for larger incisions, and the poor penetration of prophylactic antibiotics in adipose tissue.4,8 That emergency procedures were a statistically significant risk factor for SSI is also unsurprising, has previously been documented in observational studies,4 and most likely relates to rupture of the membranes prior to surgery,9 the increased urgency of procedure, and reduced attention to infection preventing behaviours. The relationship between duration of labour and SSI may be explained by increased "vulnerable time" where infection can be acquired, and due to the fact that as duration of labour increases, number of vaginal exams and likelihood of progression to an emergency procedure also rise. Other risk factors which have been shown to be statistically significant in previous observational studies were not shown to be significant in this study. In the case group, there was a trend to younger age, greater blood loss, and use of staples, though these did not reach statistical significance. This analysis is limited by its relatively small sample size, incomplete patient charts, performance at a single site, and potentially by the case finding methodology. The methodology used relies upon correct electronic coding, and so accordingly may potentially lack sensitivity. However, the 25 cases are "true" cases as confirmed by manual checking and application of CDC criteria to suspected cases, ensuring a high specificity for the case finding approach. This study has identified significant risk factors for surgical site infection post-caesarean section. Identification of these risk factors reminds obstetric staff that appropriate targeting of infection reducing strategies to women at high risk is needed. Such strategies include, but are not limited to, antibiotic prophylaxis as routine, antiseptic skin preparation, adequate glycaemic control in diabetic patients, and the use of appropriate dressings.10 Emerging strategies such as antibiotic coated sutures may also have a role.

Summary

Abstract

Aim

To identify the incidence of surgical site infection (SSI) post-caesarean section, and important contributory risk factors.

Method

A retrospective analysis was conducted to identify cases with SSI, using as a population all the caesarean sections for the 6-month period from 16 March 2009-15 September 2009 performed at Waikato Hospital (n=526). Cases (n=25) were compared with randomly selected controls (n=50) to identify important risk factors.

Results

In total, 25 of the 526 patients (5%) had a SSI post-caesarean section. Of these, 15 were revealed during the initial admission (3%), and the other 10 required hospital care post-discharge for treatment of infection (2%). The key risk factors for surgical site infection post-caesarean section identified were elevated BMI, longer duration of labour, and having an emergency procedure.

Conclusion

This study has identified significant risk factors for surgical site infection post-caesarean section. Identification of these risk factors reminds obstetric staff that appropriate targeting of infection reducing strategies to women at high risk is needed.

Author Information

Dr Marcus Ghuman, Medical student/House Officer, Auckland Hospital, Auckland; Deirdre Rohlandt, Clinical Director, Department of Obstetrics and Gynaecology, Waikato Hospital, Hamilton; Grace Joshy, Biostatistician and Senior Research Fellow, Waikato Hospital, Hamilton; Ross Lawrenson, Professor of Primary Care, Waikato Hospital, Hamilton

Acknowledgements

Correspondence

Dr Marcus Ghuman, Medical student/House Officer, Auckland Hospital, 93 Tiki Road, RD2, Te Awamutu 3872, New Zealand.

Correspondence Email

marcusghuman@hotmail.com

Competing Interests

None.

Infection Control Services. Surgical Site Infection Surveillance in Obstetrics. Waikato Hospital; 2007.National Collaborating Centre for Womens and Childrens Health. Caesarean Section. National Institute for Clinical Excellence; April 2004.Ward VP, Charlett A, Fagan J, Crawshaw SC. Enhanced surgical site infection surveillance following caesarean section: experience of a multicentre collaborative post-discharge system. J Hosp Infect. 2008;70(2):166-73.Olsen MA, Butler AM, Willers DM, et al. Risk factors for surgical site infection after low transverse cesarean section. Infect Control Hosp Epidemiol. 2008;29(6):477-84.Op 00f8ien HK, Valb 00f8 A, Grinde-Andersen A, Walberg M. Post-cesarean surgical site infections according to CDC standards: rates and risk factors. A prospective cohort study. Acta Obstet Gynecol Scand. 2007;86(9):1097-102.Walsh C, Scaife C, Hopf H. Prevention and management of surgical site infections in morbidly obese women. Obstet Gynecol.2009;113(2, Part 1):411-415.Vermillion S, Lamoutte C, Soper D, Verdeja A. Wound Infection After Cesarean: Effect of Subcutaneous Tissue Thickness. Obstet Gynecol. 2000;95(6):923-926.Lynch RJ, Ranney DN, Shijie C, et al. Obesity, surgical site infection, and outcome following renal transplantation. Ann Surg. 2009;250(6):1014-20.Nielsen T, Hokegard K. Cesarean Section and Intraoperative Surgical Complications. Acta Obstet Gynecol Scand.1984;63(2):103-108.Owens C, Stoessel K. Surgical site infections: epidemiology, microbiology and prevention. J Hosp Infect. 2008;70(S2):3-10.

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Caesarean section (CS) is one of the most common surgical procedures performed in hospitals. It is classified as a high-risk operation in the "clean" category. In New Zealand, as in other developed countries, the rate of CS has continued to rise, currently comprising over 25% of hospital births.1Surgical site infection (SSI) post-caesarean section increases maternal morbidity and costs and is thus an important problem. The benchmark SSI infection rate quoted in the RCOG green top guidelines is 6.4%;2 however, rates of SSI post CS vary widely in different publications due to differences in the criteria used to diagnose infection and varying lengths of follow-up postoperatively.3Risk factors contributing to SSI post CS are thought to include BMI, longer operation duration, age, blood loss, method of wound closure, and emergency procedures.3-6Methods This nested case-control study was conducted as a retrospective analysis using as a population all the caesarean sections for the 6 month period from 16 March 2009-15 September 2009 conducted at a single site—Waikato Hospital. Each of the patients identified in the study as having had a caesarean section was accompanied by a list of ICD9 codes. Patients with possible surgical site infections post-caesarean section were identified by manually searching through the obstetric notes of patients who had the electronic diagnostic codes "infection of obstetric surgical wound", "wound infection following a procedure", and "disruption of a caesarean section wound". CDC (US Center for Disease Control) criteria were then used to confirm infections in these cases. The case population with confirmed SSI was compared with two randomly selected (via random number generator) controls per case without SSI from the same wider 6-month population to identify any risk factors for SSI within the Waikato Hospital setting. Risk factors analysed include BMI, operation duration, age, blood loss, method of wound closure, use of prophylactic antibiotics, type of procedure, ethnicity, smoking, parity, duration of labour, and elapsed time since rupture of membranes (ROM), Statistical analysis—Categorical data were presented as frequency (percentage) and continuous data were presented as mean ± SD. Categorical variables were compared using a Chi-squared test or Fisher's exact test as appropriate. Continuous data were compared using the Kruskal-Wallis test. All P-values reported were two tailed and a P-value <0.05 was considered significant. A logistic regression of significant variables was also performed. The statistical programme SAS Version 9.1 was used for statistical analysis. Results This study identified 526 sections—192 elective lower segment caesarean sections, 331 emergency lower segment caesarean sections, and 3 emergency classical caesarean sections. In total, 25 of the 526 patients (5%) in the 6-month period analysed had a surgical site infection post-caesarean section. Of these, 15 were revealed during admission (3%), and the other 10 required hospital care post-discharge for treatment of infection (2%). The characteristics of the 25 cases and 50 controls are recorded in table 1. Table 1. Potential risk factors for post-caesarean section surgical site infection Variables Case (n=25) Control (n=50) P value Type of C-section, n (%) Emergency Elective 21 (84) 4 (16) 29 (58.0) 21 (42.0) 0.0243 Age, mean ± SD 27.2 ± 6.8 30.0 ± 6.2 0.0892 Ethnicity, n (%) Non-Maori Maori 18 (72) 7 (28) 37 (74) 13 (26.0) 1.0000 BMI (kg/m2), mean ± SD 34.7 ± 5.2 28.2 ± 6.1 0.0002 Smoking status, n (%) Smoker Non-smoker Unknown 6 (24) 13 (52) 6 (24) 19 (38) 27 (54) 4 (8) 0.4635 Parity, mean ± SD 0.7 ± 0.8 1.2 ± 1.4 0.0998 Duration of labours (hrs), mean ± SD 16.5 ± 7.6 9.5 ± 5.1 0.0019 Elapsed time since ROM (hrs), mean ± SD 17.4 ± 14.4 11.2 ± 5.1 0.2195 Operating time (mins), mean ± SD 46.8 ± 17.9 46.5 ± 13.2 0.5932 Type of closure, n (%) Sutures Staples Unknown 14 (56) 8 (32) 3 (12) 31 (62) 9 (18) 10 (20) 0.2417 Estimated blood loss (mL), mean ± SD 729 ± 475 632 ± 275 0.6044 Some data are missing for BMI, Smoking, Duration of labours, Elapsed time since ROM, type of closure, estimated blood loss. The key risk factors for surgical site infection post-caesarean section identified were elevated BMI, longer duration of labour, and having an emergency procedure. The mean BMI for the case group was 34.7kg/m2, as compared to 28.2kg/m2 in the control group (p=0.0002). Mean duration of labour in the case group was 16.5 hours, as compared to 9.5 hours in the control group (p=0.0019), and the percentage of the case group having an emergency procedure was 84%, versus 58% in the control group (p=0.0243) . Whilst cases were on average 3 years younger, had 100mls greater blood loss, and were 14% more likely to have had staples used for wound closure, these findings did not reach statistical significance. Antibiotic prophylaxis was used in all cases and controls A multivariate logistic regression was performed on the risk factors ‘type of procedure' and ‘BMI'. This regression analysis adjusted for age and BMI for the risk factor type of procedure; and adjusted for age, operating time, duration of labour, and type of procedure for the risk factor BMI. This analysis confirmed type of procedure and BMI as being independent risk factors for SSI, even after adjusting for other potentially confounding factors (see table 2). Table 2. Logistic regression of risk factors BMI and type of procedure Variables Case (n=25) Control (n=50) OR (95% CI) P value Emergency (vs elective) section, n(%) Emergency Elective Unadjusted Adjusted for age & BMI 21 (84) 4 (16) 29 (58.0) 21 (42.0) 3.80 (1.14-12.66) 4.22 (1.01-17.86) 0.0243 BMI (kg/m2), mean ± SD Unadjusted Adjusted for age Adjusted for age & operating time Adjusted for age & labour duration Adjusted for age & procedure type 34.7 ± 5.2 28.2 ± 6.1 1.21 (1.09-1.34) 1.20 (1.08-1.33) 1.20 (1.08-1.34) 1.31 (1.06-1.60) 1.22 (1.09-1.38) 0.0002 Discussion This retrospective analysis suggests that the rate of surgical site infection post-caesarean section in Waikato hospital was approximately 5% which is similar to the in-hospital rate found in other studies. However, this figure recognises only those patients requiring inpatient admission and treatment. Those who received outpatient (or no) treatment for their infection are unable to be captured by the methodology used. Thus, the total infection rate is likely to be higher than that identified in this study, as infections captured in an in-hospital setting may represent as little as one-third of the total number of infections.7 Significant risk factors for infection identified include elevated BMI, longer duration of labour, and having an emergency (as compared to an elective) procedure. The link between obesity and increased SSI risk is well established in the literature, and relates to increased subcutaneous tissue thickness (which is relatively avascular), impaired immune function, increased wound area, need for larger incisions, and the poor penetration of prophylactic antibiotics in adipose tissue.4,8 That emergency procedures were a statistically significant risk factor for SSI is also unsurprising, has previously been documented in observational studies,4 and most likely relates to rupture of the membranes prior to surgery,9 the increased urgency of procedure, and reduced attention to infection preventing behaviours. The relationship between duration of labour and SSI may be explained by increased "vulnerable time" where infection can be acquired, and due to the fact that as duration of labour increases, number of vaginal exams and likelihood of progression to an emergency procedure also rise. Other risk factors which have been shown to be statistically significant in previous observational studies were not shown to be significant in this study. In the case group, there was a trend to younger age, greater blood loss, and use of staples, though these did not reach statistical significance. This analysis is limited by its relatively small sample size, incomplete patient charts, performance at a single site, and potentially by the case finding methodology. The methodology used relies upon correct electronic coding, and so accordingly may potentially lack sensitivity. However, the 25 cases are "true" cases as confirmed by manual checking and application of CDC criteria to suspected cases, ensuring a high specificity for the case finding approach. This study has identified significant risk factors for surgical site infection post-caesarean section. Identification of these risk factors reminds obstetric staff that appropriate targeting of infection reducing strategies to women at high risk is needed. Such strategies include, but are not limited to, antibiotic prophylaxis as routine, antiseptic skin preparation, adequate glycaemic control in diabetic patients, and the use of appropriate dressings.10 Emerging strategies such as antibiotic coated sutures may also have a role.

Summary

Abstract

Aim

To identify the incidence of surgical site infection (SSI) post-caesarean section, and important contributory risk factors.

Method

A retrospective analysis was conducted to identify cases with SSI, using as a population all the caesarean sections for the 6-month period from 16 March 2009-15 September 2009 performed at Waikato Hospital (n=526). Cases (n=25) were compared with randomly selected controls (n=50) to identify important risk factors.

Results

In total, 25 of the 526 patients (5%) had a SSI post-caesarean section. Of these, 15 were revealed during the initial admission (3%), and the other 10 required hospital care post-discharge for treatment of infection (2%). The key risk factors for surgical site infection post-caesarean section identified were elevated BMI, longer duration of labour, and having an emergency procedure.

Conclusion

This study has identified significant risk factors for surgical site infection post-caesarean section. Identification of these risk factors reminds obstetric staff that appropriate targeting of infection reducing strategies to women at high risk is needed.

Author Information

Dr Marcus Ghuman, Medical student/House Officer, Auckland Hospital, Auckland; Deirdre Rohlandt, Clinical Director, Department of Obstetrics and Gynaecology, Waikato Hospital, Hamilton; Grace Joshy, Biostatistician and Senior Research Fellow, Waikato Hospital, Hamilton; Ross Lawrenson, Professor of Primary Care, Waikato Hospital, Hamilton

Acknowledgements

Correspondence

Dr Marcus Ghuman, Medical student/House Officer, Auckland Hospital, 93 Tiki Road, RD2, Te Awamutu 3872, New Zealand.

Correspondence Email

marcusghuman@hotmail.com

Competing Interests

None.

Infection Control Services. Surgical Site Infection Surveillance in Obstetrics. Waikato Hospital; 2007.National Collaborating Centre for Womens and Childrens Health. Caesarean Section. National Institute for Clinical Excellence; April 2004.Ward VP, Charlett A, Fagan J, Crawshaw SC. Enhanced surgical site infection surveillance following caesarean section: experience of a multicentre collaborative post-discharge system. J Hosp Infect. 2008;70(2):166-73.Olsen MA, Butler AM, Willers DM, et al. Risk factors for surgical site infection after low transverse cesarean section. Infect Control Hosp Epidemiol. 2008;29(6):477-84.Op 00f8ien HK, Valb 00f8 A, Grinde-Andersen A, Walberg M. Post-cesarean surgical site infections according to CDC standards: rates and risk factors. A prospective cohort study. Acta Obstet Gynecol Scand. 2007;86(9):1097-102.Walsh C, Scaife C, Hopf H. Prevention and management of surgical site infections in morbidly obese women. Obstet Gynecol.2009;113(2, Part 1):411-415.Vermillion S, Lamoutte C, Soper D, Verdeja A. Wound Infection After Cesarean: Effect of Subcutaneous Tissue Thickness. Obstet Gynecol. 2000;95(6):923-926.Lynch RJ, Ranney DN, Shijie C, et al. Obesity, surgical site infection, and outcome following renal transplantation. Ann Surg. 2009;250(6):1014-20.Nielsen T, Hokegard K. Cesarean Section and Intraoperative Surgical Complications. Acta Obstet Gynecol Scand.1984;63(2):103-108.Owens C, Stoessel K. Surgical site infections: epidemiology, microbiology and prevention. J Hosp Infect. 2008;70(S2):3-10.

For the PDF of this article,
contact nzmj@nzma.org.nz

View Article PDF

Caesarean section (CS) is one of the most common surgical procedures performed in hospitals. It is classified as a high-risk operation in the "clean" category. In New Zealand, as in other developed countries, the rate of CS has continued to rise, currently comprising over 25% of hospital births.1Surgical site infection (SSI) post-caesarean section increases maternal morbidity and costs and is thus an important problem. The benchmark SSI infection rate quoted in the RCOG green top guidelines is 6.4%;2 however, rates of SSI post CS vary widely in different publications due to differences in the criteria used to diagnose infection and varying lengths of follow-up postoperatively.3Risk factors contributing to SSI post CS are thought to include BMI, longer operation duration, age, blood loss, method of wound closure, and emergency procedures.3-6Methods This nested case-control study was conducted as a retrospective analysis using as a population all the caesarean sections for the 6 month period from 16 March 2009-15 September 2009 conducted at a single site—Waikato Hospital. Each of the patients identified in the study as having had a caesarean section was accompanied by a list of ICD9 codes. Patients with possible surgical site infections post-caesarean section were identified by manually searching through the obstetric notes of patients who had the electronic diagnostic codes "infection of obstetric surgical wound", "wound infection following a procedure", and "disruption of a caesarean section wound". CDC (US Center for Disease Control) criteria were then used to confirm infections in these cases. The case population with confirmed SSI was compared with two randomly selected (via random number generator) controls per case without SSI from the same wider 6-month population to identify any risk factors for SSI within the Waikato Hospital setting. Risk factors analysed include BMI, operation duration, age, blood loss, method of wound closure, use of prophylactic antibiotics, type of procedure, ethnicity, smoking, parity, duration of labour, and elapsed time since rupture of membranes (ROM), Statistical analysis—Categorical data were presented as frequency (percentage) and continuous data were presented as mean ± SD. Categorical variables were compared using a Chi-squared test or Fisher's exact test as appropriate. Continuous data were compared using the Kruskal-Wallis test. All P-values reported were two tailed and a P-value <0.05 was considered significant. A logistic regression of significant variables was also performed. The statistical programme SAS Version 9.1 was used for statistical analysis. Results This study identified 526 sections—192 elective lower segment caesarean sections, 331 emergency lower segment caesarean sections, and 3 emergency classical caesarean sections. In total, 25 of the 526 patients (5%) in the 6-month period analysed had a surgical site infection post-caesarean section. Of these, 15 were revealed during admission (3%), and the other 10 required hospital care post-discharge for treatment of infection (2%). The characteristics of the 25 cases and 50 controls are recorded in table 1. Table 1. Potential risk factors for post-caesarean section surgical site infection Variables Case (n=25) Control (n=50) P value Type of C-section, n (%) Emergency Elective 21 (84) 4 (16) 29 (58.0) 21 (42.0) 0.0243 Age, mean ± SD 27.2 ± 6.8 30.0 ± 6.2 0.0892 Ethnicity, n (%) Non-Maori Maori 18 (72) 7 (28) 37 (74) 13 (26.0) 1.0000 BMI (kg/m2), mean ± SD 34.7 ± 5.2 28.2 ± 6.1 0.0002 Smoking status, n (%) Smoker Non-smoker Unknown 6 (24) 13 (52) 6 (24) 19 (38) 27 (54) 4 (8) 0.4635 Parity, mean ± SD 0.7 ± 0.8 1.2 ± 1.4 0.0998 Duration of labours (hrs), mean ± SD 16.5 ± 7.6 9.5 ± 5.1 0.0019 Elapsed time since ROM (hrs), mean ± SD 17.4 ± 14.4 11.2 ± 5.1 0.2195 Operating time (mins), mean ± SD 46.8 ± 17.9 46.5 ± 13.2 0.5932 Type of closure, n (%) Sutures Staples Unknown 14 (56) 8 (32) 3 (12) 31 (62) 9 (18) 10 (20) 0.2417 Estimated blood loss (mL), mean ± SD 729 ± 475 632 ± 275 0.6044 Some data are missing for BMI, Smoking, Duration of labours, Elapsed time since ROM, type of closure, estimated blood loss. The key risk factors for surgical site infection post-caesarean section identified were elevated BMI, longer duration of labour, and having an emergency procedure. The mean BMI for the case group was 34.7kg/m2, as compared to 28.2kg/m2 in the control group (p=0.0002). Mean duration of labour in the case group was 16.5 hours, as compared to 9.5 hours in the control group (p=0.0019), and the percentage of the case group having an emergency procedure was 84%, versus 58% in the control group (p=0.0243) . Whilst cases were on average 3 years younger, had 100mls greater blood loss, and were 14% more likely to have had staples used for wound closure, these findings did not reach statistical significance. Antibiotic prophylaxis was used in all cases and controls A multivariate logistic regression was performed on the risk factors ‘type of procedure' and ‘BMI'. This regression analysis adjusted for age and BMI for the risk factor type of procedure; and adjusted for age, operating time, duration of labour, and type of procedure for the risk factor BMI. This analysis confirmed type of procedure and BMI as being independent risk factors for SSI, even after adjusting for other potentially confounding factors (see table 2). Table 2. Logistic regression of risk factors BMI and type of procedure Variables Case (n=25) Control (n=50) OR (95% CI) P value Emergency (vs elective) section, n(%) Emergency Elective Unadjusted Adjusted for age & BMI 21 (84) 4 (16) 29 (58.0) 21 (42.0) 3.80 (1.14-12.66) 4.22 (1.01-17.86) 0.0243 BMI (kg/m2), mean ± SD Unadjusted Adjusted for age Adjusted for age & operating time Adjusted for age & labour duration Adjusted for age & procedure type 34.7 ± 5.2 28.2 ± 6.1 1.21 (1.09-1.34) 1.20 (1.08-1.33) 1.20 (1.08-1.34) 1.31 (1.06-1.60) 1.22 (1.09-1.38) 0.0002 Discussion This retrospective analysis suggests that the rate of surgical site infection post-caesarean section in Waikato hospital was approximately 5% which is similar to the in-hospital rate found in other studies. However, this figure recognises only those patients requiring inpatient admission and treatment. Those who received outpatient (or no) treatment for their infection are unable to be captured by the methodology used. Thus, the total infection rate is likely to be higher than that identified in this study, as infections captured in an in-hospital setting may represent as little as one-third of the total number of infections.7 Significant risk factors for infection identified include elevated BMI, longer duration of labour, and having an emergency (as compared to an elective) procedure. The link between obesity and increased SSI risk is well established in the literature, and relates to increased subcutaneous tissue thickness (which is relatively avascular), impaired immune function, increased wound area, need for larger incisions, and the poor penetration of prophylactic antibiotics in adipose tissue.4,8 That emergency procedures were a statistically significant risk factor for SSI is also unsurprising, has previously been documented in observational studies,4 and most likely relates to rupture of the membranes prior to surgery,9 the increased urgency of procedure, and reduced attention to infection preventing behaviours. The relationship between duration of labour and SSI may be explained by increased "vulnerable time" where infection can be acquired, and due to the fact that as duration of labour increases, number of vaginal exams and likelihood of progression to an emergency procedure also rise. Other risk factors which have been shown to be statistically significant in previous observational studies were not shown to be significant in this study. In the case group, there was a trend to younger age, greater blood loss, and use of staples, though these did not reach statistical significance. This analysis is limited by its relatively small sample size, incomplete patient charts, performance at a single site, and potentially by the case finding methodology. The methodology used relies upon correct electronic coding, and so accordingly may potentially lack sensitivity. However, the 25 cases are "true" cases as confirmed by manual checking and application of CDC criteria to suspected cases, ensuring a high specificity for the case finding approach. This study has identified significant risk factors for surgical site infection post-caesarean section. Identification of these risk factors reminds obstetric staff that appropriate targeting of infection reducing strategies to women at high risk is needed. Such strategies include, but are not limited to, antibiotic prophylaxis as routine, antiseptic skin preparation, adequate glycaemic control in diabetic patients, and the use of appropriate dressings.10 Emerging strategies such as antibiotic coated sutures may also have a role.

Summary

Abstract

Aim

To identify the incidence of surgical site infection (SSI) post-caesarean section, and important contributory risk factors.

Method

A retrospective analysis was conducted to identify cases with SSI, using as a population all the caesarean sections for the 6-month period from 16 March 2009-15 September 2009 performed at Waikato Hospital (n=526). Cases (n=25) were compared with randomly selected controls (n=50) to identify important risk factors.

Results

In total, 25 of the 526 patients (5%) had a SSI post-caesarean section. Of these, 15 were revealed during the initial admission (3%), and the other 10 required hospital care post-discharge for treatment of infection (2%). The key risk factors for surgical site infection post-caesarean section identified were elevated BMI, longer duration of labour, and having an emergency procedure.

Conclusion

This study has identified significant risk factors for surgical site infection post-caesarean section. Identification of these risk factors reminds obstetric staff that appropriate targeting of infection reducing strategies to women at high risk is needed.

Author Information

Dr Marcus Ghuman, Medical student/House Officer, Auckland Hospital, Auckland; Deirdre Rohlandt, Clinical Director, Department of Obstetrics and Gynaecology, Waikato Hospital, Hamilton; Grace Joshy, Biostatistician and Senior Research Fellow, Waikato Hospital, Hamilton; Ross Lawrenson, Professor of Primary Care, Waikato Hospital, Hamilton

Acknowledgements

Correspondence

Dr Marcus Ghuman, Medical student/House Officer, Auckland Hospital, 93 Tiki Road, RD2, Te Awamutu 3872, New Zealand.

Correspondence Email

marcusghuman@hotmail.com

Competing Interests

None.

Infection Control Services. Surgical Site Infection Surveillance in Obstetrics. Waikato Hospital; 2007.National Collaborating Centre for Womens and Childrens Health. Caesarean Section. National Institute for Clinical Excellence; April 2004.Ward VP, Charlett A, Fagan J, Crawshaw SC. Enhanced surgical site infection surveillance following caesarean section: experience of a multicentre collaborative post-discharge system. J Hosp Infect. 2008;70(2):166-73.Olsen MA, Butler AM, Willers DM, et al. Risk factors for surgical site infection after low transverse cesarean section. Infect Control Hosp Epidemiol. 2008;29(6):477-84.Op 00f8ien HK, Valb 00f8 A, Grinde-Andersen A, Walberg M. Post-cesarean surgical site infections according to CDC standards: rates and risk factors. A prospective cohort study. Acta Obstet Gynecol Scand. 2007;86(9):1097-102.Walsh C, Scaife C, Hopf H. Prevention and management of surgical site infections in morbidly obese women. Obstet Gynecol.2009;113(2, Part 1):411-415.Vermillion S, Lamoutte C, Soper D, Verdeja A. Wound Infection After Cesarean: Effect of Subcutaneous Tissue Thickness. Obstet Gynecol. 2000;95(6):923-926.Lynch RJ, Ranney DN, Shijie C, et al. Obesity, surgical site infection, and outcome following renal transplantation. Ann Surg. 2009;250(6):1014-20.Nielsen T, Hokegard K. Cesarean Section and Intraoperative Surgical Complications. Acta Obstet Gynecol Scand.1984;63(2):103-108.Owens C, Stoessel K. Surgical site infections: epidemiology, microbiology and prevention. J Hosp Infect. 2008;70(S2):3-10.

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