Successful, but incomplete control of a Serratia marcescens blaIMP-4 outbreak related to contaminated hand basin waste-water systems

Mr John Greenough1, Ms Trudi Bannam1, Prof Lindsay Grayson1,3, Prof Paul Johnson1,3, Ms Elizabeth Grabsch1, Ms Deidre Edmonds1, Dr Marcel Leroi1, Ms Liz Orr1, Dr Jason Kwong1,3, Dr Shanti Narayanasamy1, Dr Susan Ballard2, Prof Ben Howden1,2,3

1Austin Hospital Infectious Diseases, Microbiology and Infection Control Department, Heidelberg, VIC, Australia
2Microbiological Diagnostic Unit (MDU) Public Health Laboratory, Parkville, VIC, Australia
3University of Melbourne, Parkville, VIC, Australia


Background: Serratia marcescens is a common healthcare associated infection that is intrinsically resistant to colistin and is occasionally linked to environmental contamination. After the identification of a number of clinical (n=2) and faecal colonization (n=5) isolates of carbapenem-resistant S. marcescens producing blaIMP-4 (SM-IMP4), we investigated potential environmental reservoirs in our hospital.

Materials/methods: Following an initial broad-based assessment of potential reservoirs, the drains of clinical hand basins (CHBs) in key clinical wards, were cultured. Flocked swab samples underwent tryptone soy broth enrichment followed by sub-culture onto CHROMagar ESBL media. Potential ESBL-producing Gram-negative isolates were identified (MALDI-TOF). Carbapenem-resistant isolates were assessed for carbapenemase production (Carba-blue test and if Carba-blue positive by PCR) and by whole genome sequencing (WGS). A detailed manual CHB cleaning program using detergent to remove visible biofilm was conducted throughout the hospital.

Results: Of 400 CHBs on 22 wards 72/400 (18%) grew CPE (70/72 SM-IMP4; 1/72 K. pneumoniae-IMP4; 1/72 SM-OXA1), with 11/22 wards positive. Most CHBs were heavily choked with biofilm material. Environmental and clinical isolates were highly related by WGS. Marked reductions in CHB SM-IMP4 colonisation were noted post-cleaning (e.g. ICU: 25/33 vs 10/33; Spinal: 10/17 vs 3/17). Only one case of faecal SM-IMP4 colonisation has been detected 12 months since cleaning the CHBs.

Conclusions: We identified biofilm-laden CHBs to be a major reservoir for SM-IMP4 and to be tightly linked to patient cases of SM-IMP4 colonisation/infection. Simple, but detailed, cleaning controlled the outbreak. Annual cleaning of CHB drains and education of staff are ongoing.


John Greenough is the Manager of the Infection Control Department at Austin Hospital Melbourne. He has 22 years experience as Infection Control consultant working at Austin Hospital and previously St. Vincent’s Hospital Melbourne. Since 2012 John has gained both interest and experience in managing outbreaks of Carbapenemase Producing Enterobacteriaceae (CPE).

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