Aim
The aim of this study was to investigate the incidence of superficial surgical site infection and deep surgical site infection, and to analyze whether antibiotic prophylaxis is cost-reducing in elective cesarean section in Örebro County, Sweden. This county has around 270,000 inhabitants and is situated in central Sweden.
Participation characteristics
All women undergoing elective cesarean section from 1 January 2011 to 31 December 2012 at the Departments of Obstetrics and Gynecology at Örebro University Hospital and Karlskoga Hospital were eligible for the study. The extent of the time period for inclusion was decided according to the yearly number of women delivered by elective cesarean section at the hospitals and the incidence of postoperative infections earlier described in a Swedish population [7]. Exclusion criteria were having received antibiotic prophylaxis or having been treated with prophylactic antibiotics (for example due to urinary tract anomaly), having left Örebro County after delivery or not having been followed up by the Region Örebro County health care system for any other reason, having been reoperated due to causes other than wound infection, and having undergone other major procedures during the cesarean section.
Of a total of 6871 women delivered in Örebro County between 2011 and 2012, 365 (5.3%) underwent elective cesarean section. Of these, 47 were excluded (Fig. 1). The main reason for exclusion was having received antibiotic prophylaxis, and another important reason was having moved out of the county. The mean age was 32.5 years, 24% were obese, 4% had diabetes mellitus, and 4% were smokers.
Process
The women were identified through the search function in the Obstetrix medical record system (Siemens, version 2.14.02.200). Medical records from primary health care, maternity health care, specialist maternity health care, and obstetric in-patient care in Örebro County were studied. The following possible risk factors for infection were registered: smoking, any type of diabetes mellitus, obesity (BMI > 30 kg/m2), excessive perioperative hemorrhage (> 1000 ml), and postoperative thromboprophylaxis; the first three of these were extracted from maternity health care records and the others were extracted from obstetric in-patient care unit records. Postoperative infections were classified as superficial surgical site infection and deep surgical site infection developing up to 30 days postoperatively, according to the Centers for Disease Control definitions of nosocomial surgical infections [16]. Deep surgical site infection was considered equal to endometritis, which is the term used in the two meta-analyses cited previously [3, 7]. Urinary tract infections were excluded since there is no evidence they are preventable by antibiotic prophylaxis [7].
To minimize the risk of underreporting the incidence of postoperative infections, all health care visits during the first 30 days after each cesarean section were identified and studied. One woman with a deep surgical site infection and several women with superficial surgical site infections were treated in units other than the Departments of Obstetrics and Gynecology at the two hospitals.
Intervention
All participants were assumed to receive antibiotic prophylaxis.
Comparison
The same participants not receiving any antibiotic prophylaxis.
Economic analysis
A health care perspective was used in the analysis, meaning that only health care costs were included. The intervention cost and the cost of infections developed during the first month after delivery were considered. The care costs preventable by an introduction of antibiotic prophylaxis were calculated assuming the same effect of antibiotic prophylaxis as in the meta-analysis cited earlier [7], namely, a relative reduction in the risk of endometriosis (0.62, or 95% CI 0.47–0.82) and of superficial wound infection (0.38, or 95% CI 0.24–0.61) after elective cesarean section. Finally, the care costs preventable by antibiotic prophylaxis were compared to the costs for administering antibiotics to all women undergoing elective cesarean section during the given time period.
Costs for antibiotic prophylaxis were obtained from the Swedish Medicines Compendium for health care professionals (FASS). Where prices were not fixed, costs were obtained from the pharmacy at Örebro University Hospital. The costs of administering antibiotic prophylaxis (ampicillin 2 g intravenously) included both material and personnel costs (the latter including salaries and payroll tax). Estimated time required was acquired from the head of the ward caring for women undergoing elective cesarean section at Örebro University Hospital, and the costs of material and personnel time were acquired from Örebro University Hospital accounts. It was assumed that two-thirds of an employee’s time is spent on patient care, and the rest on activities such as preparation, further education, meetings, and breaks.
Costs for the in-patient care of the postoperative infections were extracted from the Region Örebro County accounting system (ECOMED). Costs for all in-patient care are registered in this system according to a Swedish system called cost per patient (KPP), which is mainly used for debiting patient costs from other counties. The KPP encompasses all hospital health care in Sweden, and is used to produce national average costs for a certain treatment of a certain disease. Costs for out-patient care were calculated using the standard prices for out-patient visits that are used to debit patient costs from other counties.
Costs were calculated at the 2014 price level and expressed in Euro, transformed from Swedish Crowns using exchange rate 1 Euro = 9 Swedish Crowns. Overhead costs for the health authority were included in the costs for care of postoperative infections but not in the costs for administering antibiotic prophylaxis. To ensure comparability, proportions of overhead costs were estimated and then excluded from the costs of care for postoperative infections.
Three alternative assumptions were tested in a sensitivity analysis:
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Half of an employee’s time instead of 2/3 is spent on patient care.
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15% of overhead costs instead of 9%.
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The effect of antibiotic prophylaxis is reduced according to the lower end of 95% confidence interval presented in the meta-analysis [7]; 47% instead of 62% for endometritis and 24% instead of 38% for superficial wound infection.
Statistics analysis
Descriptive data are presented as absolute numbers and percentages. The risk of infection was calculated in a univariate analysis as odds ratios (ORs) with 95% confidence intervals (CIs). Version 22 of the IBM SPSS software package was used for the statistical calculation. Statistical uncertainty of the incidence of infections was calculated using release 11 of the STATA software package (STATA, TX, USA). Average cost reductions and corresponding 95% credible intervals as well as probability of cost-saving were estimated using a resampling method with replacement and 10,000 replications in version 3.2.2 of the R statistical software package [17].