This study will be conducted over three years with an estimated sample size of 4500 patients. Prior to enrollment of study subjects, each year will be divided into 3-month blocks and each block will be assigned one of the two study antiseptic solutions - 2% chlorhexidine gluconate in 70% isopropyl alcohol (CA) or 10% Povidone-Iodine (PI) - in an alternating manner. All patients undergoing elective cesarean deliveries during a block will receive the same preoperative skin preparation, in concordance with guidelines for its use. The block assignments will alternate within each year and the order will be reversed after one year to minimize or eliminate seasonal variation in skin infection rates. All patients will receive routine history and physical examination, blood tests, pre-procedure bathing instructions, and preoperative body hair clipping as desired by their primary obstetric provider. Age, body mass index (BMI), gestational age, history of smoking, previous abdominal surgery, number of pregnancies, and live births will be documented before entry into the study. Eligible patients will receive antibiotic prophylaxis with weight-based cefazolin within 60 min before skin incision. We will collect data on preoperative preparation of the surgical site (clipping vs. shaving), type of skin and uterine incision, method of fascia and skin closure, duration of the procedure, use of postoperative antibiotics, and adverse reactions to the skin preparation. The primary endpoint for this study will be any SSI diagnosed within 30 days of cesarean delivery. Our secondary outcomes will be the type of SSI (based on the Center for Disease Control infection classification) and the time to diagnosis of SSI.

The Infectious Disease department at BWH will perform the surveillance for SSI/endometritis. This team will be blinded to the choice of anti-sepsis preparation during the study period. Briefly, surveillance will include daily, weekly, monthly, and quarterly reviews of data. The infectious disease team will perform a daily review of microbiology results for positive wound and blood cultures, and assess whether the patient had cesarean section within 30 days prior to cultures. On a weekly basis, a report of obstetric patients readmitted within 30 days will be generated, and patients will be selected with an admitting diagnosis consistent with infection in the setting of a history of recent cesarean delivery. Each month, a report of patients will be generated with ICD-9 discharge code for cesarean section as well as ICD-9 codes for other complications of obstetrical surgical wound and major puerperal infection. Post-cesarean delivery patients receiving antibiotics for at least 2 days after the first postoperative day, and those that receive antibiotics during readmission will also be identified and recorded. During every quarter, the number of elective cesarean deliveries performed will be quantified, and the incidence of specific sub-types of SSI (superficial, deep, organ space/endometritis) will be documented. In addition to inpatient surveillance, the electronic clinic records for all patients will be reviewed, and data will be recorded for any SSI that is diagnosed and treated on an outpatient basis. Documentation from discharge to the six-week postpartum visit will be reviewed to ensure data fidelity, but only infections that occur within 30 days of cesarean delivery will be included in the final analyses. Active SSI will be treated according to prevailing guidelines.