Outbreak of Enterobacter cloacae related to understaffing, overcrowding, and poor hygiene practices

OBJECTIVE: To determine the cause and mode of transmission of a cluster of infections due to Enterobacter cloacae. DESIGN AND SETTING: Retrospective cohort study in a neonatal intensive-care unit (NICU) from December 1996 to January 1997; environmental and laborato ry investigations. SUBJECTS: 60 infants hospitalized in the NICU during the outbreak period. MAIN OUTCOME MEASURES: Odds ratios (OR) linking E cloacae colonization or i nfection and various exposures. All available E cloacae isolates were typed and characterized by contour-clamped homogenous electric-field electrophor esis to confirm possible cross-transmission. RESULTS: Of eight case-patients, two had bacteremia; one, pneumonia; one, s oft-tissue infection; and four, respiratory colonization. Infants weighing <2,000 g and born before week 33 of gestation were more likely to become ca ses (P<.001). Multivariate analysis indicated that the use of multidose via ls was independently associated with E cloacae carriage (OR, 16.3; 95% conf idence interval [CI95,], 1.8 infinity; P=.011). Molecular studies demonstra ted three epidemic clones. Cross-transmission was facilitated by understaff ing and overcrowding (up to 25 neonates in a unit designed for 15), with an increased risk of E cloacae carriage during the outbreak compared to perio ds without understaffing and overcrowding (relative risk, 5.97; CI95, 2.2-1 6.4). Concurrent observation of healthcare worker (HCW) handwashing practic es indicated poor compliance. The outbreak was terminated after decrease of work load, increase of hand antisepsis, and reinforcement of single-dose m edication. CONCLUSIONS: Several factors caused and aggravated this outbreak: (1) intro duction of E cloacae into the NICU, likely by two previously colonized infa nts; (2) further transmission by HCWs' hands, facilitated by substantial ov ercrowding and understaffing in the unit; (3) possible contamination of mul tidose vials with E cloacae. Overcrowding and understaffing in periods of i ncreased work load may result in outbreaks of nosocomial infections and sho uld be avoided (Infect Control Hosp Epidemiol 1999;20:598-603).