Hindawi Publishing Corporation Infectious Diseases in Obstetrics and Gynecology Volume 2011, Article ID 267249, 8 pages doi:10.1155/2011/267249 Research Article The Emergence of Clostridium difficile Infection among Peripartum Women: A Case-Control Study of a C. difficile Outbreak on an Obstetrical Service Jennifer A. Unger, 1 Estella Whimbey, 2 Michael G. Gravett, 1 and David A. Eschenbach 1 1 Department of Obstetrics and Gynecology, University of Washington, Seattle, P.O. Box 356460, WA 98195-6460, USA 2 Department of Medicine, University of Washington Medical Center, Seattle, WA 98195-0001, USA Correspondence should be addressed to Jennifer A. Unger, junger@u.washington.edu Received 1 November 2010; Revised 12 April 2011; Accepted 25 May 2011 Academic Editor: Patrick Ramsey Copyright © 2011 Jennifer A. Unger et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Objective. An outbreak of 20 peripartum Clostridium difficile infections (CDI) occurred on the obstetrical service at the University of Washington Medical Center (UWMC) between April 2006 and June 2007. In this report, we characterize the clinical manifestations, describe interventions that appeared to reduce CDI, and determine potential risk factors for peripartum CDI. Methods. An investigation was initiated after the first three peripartum CDI cases. Based on the findings, enhanced infection control measures and a modified antibiotic regimen were implemented. We conducted a case-control study of peripartum cases and unmatched controls. Results. During the outbreak, there was an overall incidence of 7.5 CDI cases per 1000 deliveries. Peripartum CDI infection compared to controls was significantly associated with cesarean delivery (70% versus 34%; P = 0.03 ), antibiotic use (95% versus 56%; P = 0.001), chorioamnionitis (35% versus 5%; P = 0.001), and the use of the combination of ampicillin, gentamicin, and clindamycin (50% versus 3%; P< 0.001 ). Use of combination antibiotics remained a significant independent risk factor for CDI in the multivariate analysis. Conclusions. The outbreak was reduced after the implementation of multiple infection control measures and modification of antibiotic use. However, sporadic CDI continued for 8 months after these measures slowed the outbreak. Peripartum women appear to be another population susceptible to CDI. 1. Introduction The patient populations susceptible to Clostridium difficile infection (CDI) have now broadened to include pregnant women. In nonpregnant populations, both the incidence and severity of CDI have increased over the past decade. Recent large CDI outbreaks in Canada and U.S.A. demonstrated an increase CDI infection rate from a baseline of 2–6 infections per 1,000 hospitalized discharges (HD) in the 1990’s [1–3] to 10–20 infections per 1,000 HD during recent outbreaks [4, 5]. As with nonpregnant patients, the incidence of CDI also has increased significantly in peripartum women. Using the Nationwide Inpatient Sample of all payer U.S. hospital discharges, the number of nationally reported peripartum CDI cases doubled from 129 cases in 1998 to 294 cases in 2006; the estimated CDI incidence among peripartum women increased significantly from about 0.4 to 0.7 per 100,000 deliveries over this period [6]. While the apparent lower rate of CDI in peripartum than nonpregnant patients explains the sporadic reporting of peripartum CDI [7–10], severe manifestations including septic shock, toxic mega colon, and even death occur in the peripartum population [8–10]. Antibiotics significantly decrease both maternal and neonatal infections, but they also are the primary risk factor for CDI, the leading cause of nosocomial infectious diarrhea [11]. Antibiotics disrupt normal bowel flora and promote colonic C. difficile overgrowth and subsequent exotoxin production. Prolonged antibiotic and multiple antibiotic uses are particularly associated with CDI [12]. Exposure to