Y-025. Implementation of a Novel PFGE Protocol for Group B Streptococcus Surveillance: A Neonatal Intensive Care Unit Case Study

A. M. Woron, J. K. MacFarquhar, J. P. Dill, M. Lehman, J. A. Gibson;
Tennessee Dept. of Hlth., Nashville, TN.

Infection with Group B Streptococcus (GBS) is the leading cause of neonatal sepsis and meningitis. In September 2007, the Tennessee Department of Health was notified of an outbreak of late-onset GBS sepsis in a neonatal intensive care unit (NICU). A pulsed-field gel electrophoresis (PFGE) protocol was developed to assist the epidemiology section in determining if the increase represented an outbreak requiring further investigation to identify the source of infection and prevent additional cases. A review of all 2007 NICU reports for GBS was conducted, followed by serotyping, PFGE, and multilocus sequence typing (MSLT) on case patient isolates. PFGE was performed on nine suspect cases and 32 unrelated isolates. Seven epi-related isolates were serotyped and three representative samples were tested by MLST. A literature search revealed limited examples of applying PFGE to GBS. None of the existing published protocols utilized the PulseNet global standard, Salmonella Braenderup H9812. A PFGE method was developed utilizing the PulseNet H9812 global standard. Tenover criteria were used to implicate related isolates for further investigation. Three distinct PFGE pattern groups, two serotypes (Ia and II), and a common MLST pattern ST23 and ST23 variant with a new allele were identified among the outbreak implicated isolates. Three isolates were indistinguishable with PFGE and MLST. The use of a novel PFGE protocol indicated the need for a full epidemiology investigation. This investigation indicated that multiple factors may have contributed to the outbreak occurring. Findings suggested a common source for three of the cases. PFGE and MLST results indicated that the GBS outbreak was multiclonal. The use of the PFGE H9812 global standard and universal running conditions sets the stage for multi-jurisdictional normalization and comparison of results. Rapid epidemiologic investigation and molecular subtyping resulted in identification of multiple transmission pathways, implementation of control measures, and cessation of transmission.