Quantifying the relative effect of environmental contamination on surgical ward MRSA incidence: An exploratory analysis.

ABSTRACT

BACKGROUND: To investigate and quantify the contribution of environmental contamination towards methicillin-resistant Staphylococcus aureus (MRSA) incidence observed in a hospital ward using stochastic modelling. METHODS: A non-homogeneous Poisson process model was developed to investigate the relationship between environmental contamination and MRSA incidence in a UK surgical ward during a cleaning intervention study. The model quantified the fractional risks (FRs) from colonised patients, environmental contamination and a generic background source as a measure of their relative importance in describing the observed MRSA incidence. RESULTS: While the background source remained the most likely MRSA acquisition source for this ward (as measured by the FRs), environmental contamination was the second most likely source, ahead of colonised patients in the ward. The relative importance of environmental contamination was smaller in the enhanced cleaning period compared with the normal cleaning period, albeit with notable variability in the estimates. CONCLUSIONS: Accounting for environmental contamination in stochastic modelling of MRSA transmission within a hospital ward provides a richer interpretation of the FRs, and is particularly pertinent in quantitative investigations of hospital cleaning interventions to reduce MRSA acquisition.