SERRATIA-MARCESCENS OUTBREAK ASSOCIATED WITH EXTRINSIC CONTAMINATION OF 1-PERCENT CHLORXYLENOL SOAP

OBJECTIVES: To determine risk factors for Serratia marcescens infectio n or colonization, and to identify the source of the pathogen and fact ors facilitating its persistence in a neonatal intensive-care unit (NI CU) during an outbreak. DESIGN: Retrospective case-control study; revi ew of NICU infection control policies, soap use, and handwashing pract ices among healthcare workers (HCWs); and selected environmental cultu res. SETTING: A university-affiliated tertiary-care hospital NICU. PAT IENTS: All NICU infants with at least one positive culture for S marce scens during August 1994 to October 1995. infants who did not develop S marcescens infection or colonization were selected randomly as contr ols. RESULTS: Thirty-two patients met the case definition. On multivar iate analysis, independent risk factors for S marcescens infection or colonization were having very low birth weight (<1,500 g), a patent du ctus arteriosus, a mother with chorioamnionitis, or exposure to a sing le HCW. During January to July 1995, NICU HCWs carried their own bottl es of 1% chlorxylenol soap, which often were left standing inverted in the NICU sink and work areas. Cultures of 16 (31% of 52 samples of so ap and I (8%) of 13 sinks yielded S marcescens. The 16 samples of soap all came from opened 4-oz bottles carried by HCWs. DNA banding patter ns of case infant, HCW soap bottle, and sink isolates were identical. CONCLUSIONS: Extrinsically contaminated soap contributed to an outbrea k of S marcescens infection. Very-low-birth-weight infants with multip le invasive procedures and exposures to certain HCWs were at greatest risk of S marcescens infection or colonization.