Serratia marcescens in the neonatal intensive care unit: A cluster investigation using molecular methods

Serratia marcescens (S. marcescens) is associated with nosocomial infections with significant morbidity and mortality in the neonatal intensive care units (NICU). We describe the control of a multi-clonal S. marcescens infections outbreak in our tertiary-level NICU and the application of molecular typing using repetitive element palindromic PCR (rep-PCR) and next generation sequencing (NGS) in the investigation.

Outbreak investigation was performed where clinical, spatial and epidemiologic links were established. Screening of all infants in the NICU and the environment was performed. Rep-PCR and NGS methods were used to identify potential environmental sources of infections and clustering among cases.

Eleven cases were detected during the outbreak period: mean gestational age 27 weeks (range: 24-32), predominantly male (82%), mean age of infection 24 days (range: 6-51). Six infants were treated for conjunctivitis and one for bacteraemia. Identification of colonized infant via a point prevalence survey and cohorting of all infected/colonized patients were implemented. We performed environmental swabbing of surfaces, water outlets, chlorhexidine hand wash solutions and hand hygiene hand rubs. Both rep-PCR and NGS classified the 11 case isolates into 5 types. No point source was identified except for a single positive environmental isolate from a sink which was clonally distinct from the cases.

Identification and cohorting of infected/colonized patient was important in the control of S. marcescens outbreak in the NICU. The utility of rep-PCR was comparable to NGS in providing molecular information to develop S. marcescens outbreak control strategies.