Management and investigation of a Serratia marcescens outbreak in a neonatal unit in Switzerland – the role of hand hygiene and whole genome sequencing

Walter Zingg, Isabelle Soulake, Damien Baud, Benedikt Huttner, Riccardo Pfister, Gesuele Renzi, Didier Pittet, Jacques Schrenzel, Patrice Francois

Many outbreaks due to Serratia marcescens among neonates have been described in the literature but little is known about the role of whole genome sequencing in outbreak analysis and management. Between February and March 2013, 2 neonates and 2 infants previously hospitalised in the neonatal unit of a tertiary care centre in Switzerland, were found to be colonised with S. marcescens. An investigation was launched with extensive environmental sampling and neonatal screening in four consecutive point prevalence surveys between April and May 2013. All identified isolates were first investigated by fingerprinting and later by whole genome sequencing. Audits of best practices were performed and a hand hygiene promotion programme was implemented. Twenty neonates were colonised with S. marcescens. No invasive infection due to S. marcescens occurred. All 231 environmental samples were negative. Hand hygiene compliance improved from 51% in April 2013 to 79% in May 2013 and remained high thereafter. No S. marcescens was identified in point prevalence surveys in June and October 2013. All strains were identical in the fingerprinting analysis and closely related according to whole genome sequencing. Improving best practices and particularly hand hygiene proved effective in terminating the outbreak. Whole genome sequencing is a helpful tool for genotyping because it allows both sufficient discrimination of strains and comparison to other outbreaks through the use of an emerging international database.