Neonatal Intensive Care Unit Outbreak of Extended-Spectrum â-Lactamase Producing Escherichia coli and Associated Risk Factors, Los Angeles County, 2013

BACKGROUND: In November 2013, Los Angeles County (LAC) Department of Public Health (DPH) was notified of five patients in a neonatal intensive care unit (NICU) with cultures positive for extended-spectrum β-lactamase (ESBL) producing Escherichia coli between October 1, 2013 and November 26, 2013. This is the first occurrence of an ESBL E. coli outbreak in a LAC NICU; few ESBL E. coli NICU outbreaks are documented. An outbreak investigation and matched case-control study was conducted.

METHODS: A case was defined as a patient in the NICU who had a newly positive ESBL E.coli culture from October 1, 2013 to December 4, 2013. Controls were randomly selected from neonates who had been in the NICU from October 1, 2013 to December 4, 2013. Three controls, matched on gender and born within three weeks gestation of the respective case, were selected for each case. We calculated the odds ratio for infection based on known risk factors found in the literature, controlling for gender. The facility conducted surveillance cultures on all neonates, NICU healthcare staff, and performed environmental sampling. Isolates were sent to the LAC public health lab for pulsed-field gel electrophoresis (PFGE). Staffing rosters for physicians, nurses, and respiratory therapists were analyzed.

RESULTS: Five cases were identified, and 15 controls selected. Cases had positive cultures from eye drainage (n=2), umbilicus (n=2), and blood (n=1). The staffing analyses showed direct care overlap in physicians, respiratory therapists, and nurses among cases.  Two distinct PFGE clusters were identified, A and B. Cases 1 and 5 had indistinguishable PFGEs (Cluster A). Cases 2 and 3 had slight band differences indicating they were possibly related to Cluster A. Case 4 had a matching PFGE with a nurse (Cluster B). Environmental samples were negative. Factors identified for increased odds of infection were gestational age, birth weight, peripherally inserted central catheter line presence, and receipt of a blood transfusion (p<0.05).

CONCLUSIONS: Two distinct clusters resulted in the first LAC NICU outbreak of a highly resistant organism. As with NICU outbreaks with other organisms, we found that low gestational age and birth weight were significant risk factors. Neonates at lower gestational age tend to be at greater risk for infection with ESBL E. coli compared to older neonates. No point source was identified; however, we hypothesize healthcare worker transmission is a possible mode of acquisition. After implementing cohorting, hand hygiene surveillance, and infection control measures, there were no additional cases.