An Outbreak of Serratia marcescens Bacteremia Traced to Contamination of Intravenous Magnesium Sulfate Solution

BACKGROUND/OBJECTIVES: Previous outbreaks of Serratia marcescens (SM) have been associated with contaminated medical equipment, IV fluids and inadequate hand hygiene. In March 2005, the New Jersey Department of Health was notified of a cluster of SM bloodstream infections (BSIs). We investigated to determine the source of the outbreak and implement control measures. METHODS: We defined cases as SM BSI with onset date after January 2005. Medical records of cases were reviewed to identify risk factors for SM BSI. Medical equipment, medications, IV solutions, tap water and the hands of health care workers were tested for the presence of SM. SM isolates recovered from patients and environmental sampling were submitted to CDC for analysis by pulsed-field gel electrophoresis (PFGE). RESULTS: Five cases, with range of illness onset from March 2-10, 2005 were identified. Of these, three were men. Median age was 75 years (range: 17-79). All case-patients were admitted for cardiovascular surgery (CS) and had received IV magnesium sulfate (MS) less than 48 hours before sepsis onset. SM was isolated from a bag of MS solution administered to one patient and from an unopened MS solution bag; both bags were supplied premixed from the same company and had identical lot numbers. SM isolates from the five patients and the two bags of MS had identical PFGE patterns. After the use of premixed MS solutions from the implicated company was discontinued, no further SM BSIs were identified. CONCLUSIONS: Contaminated MS solutions caused this outbreak of SM BSI among CS patients. This led to a multi-state investigation of similar outbreaks and eventual recall of a nationally distributed product. Infection control professionals should consider exposure to intrinsically contaminated parenteral solutions in unusual clusters of hospitalized patients who develop BSI.