Outbreak of Multidrug-Resistant <i>Serratia marcescens</i> Infection in a Neonatal Intensive Care Unit

<jats:sec id="S0195941700026825_abs1"><jats:title>Background.</jats:title><jats:p><jats:italic>Serratia marcescens</jats:italic> causes healthcare-associated infections and significant morbidity and mortality in neonatal intensive care units (NICUs). We report the investigation and control of an outbreak of multidrug-resistant (MDR) <jats:italic>S. marcescens</jats:italic> infection at an NICU.</jats:p></jats:sec><jats:sec id="S0195941700026825_abs2"><jats:title>Methods.</jats:title><jats:p>An outbreak investigation and a case-control study were undertaken at a 36-bed NICU in a tertiary care hospital in Baltimore, Maryland, for the period from October 2004 through February 2005. The outbreak investigation included case identification, review of medical records, environmental cultures, patient surveillance cultures, personnel hand cultures, and pulsed-field gel electrophoresis (PFGE). The case-control study included case identification and review of medical records. Infection control measures were implemented. Eighteen NICU neonates had cultures that grew MDR <jats:italic>S. marcescens</jats:italic> during the study period. The case-control study included 16 patients with the outbreak strain or an unidentified strain of MDR <jats:italic>S. marcescens</jats:italic> and 32 control patients not infected and/or colonized with MDR <jats:italic>S. marcescens,</jats:italic> treated in the NICU for at least 48 hours during the study period.</jats:p></jats:sec><jats:sec id="S0195941700026825_abs3"><jats:title>Results.</jats:title><jats:p>PFGE analysis identified a single strain of MDR S. <jats:italic>marcescens</jats:italic> that infected or colonized 15 patients. Two patients had unique strains, and 1 patient's isolate could not be subtyped. An unrelated MDR <jats:italic>S. marcescens</jats:italic> isolate was recovered from a sink drain. Exposure to inhalational therapy was an independent risk factor for MDR <jats:italic>S. marcescens</jats:italic> acquisition after adjusting for birth weight. Extensive investigation failed to reveal a point source for the outbreak.</jats:p></jats:sec><jats:sec id="S0195941700026825_abs4"><jats:title>Conclusion.</jats:title><jats:p>A single epidemic strain of MDR <jats:italic>S. marcescens</jats:italic> spread rapidly and threatened to become endemic in this NICU. Transient carriage on the hands of healthcare personnel or on respiratory care equipment was the likely mode of transmission. Cohorting patients and staff, at the cost of bed closures and additional personnel, interrupted transmission and halted the outbreak.</jats:p></jats:sec>