Transmission dynamics of epidemic methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci in England and Wales.

A simple epidemiological framework for the analysis of the transmission dynamics of hospital outbreaks of epidemic methicillin-resistant Staphylococcus aureus (EMRSA) and vancomycin-resistant enterococci (VRE) in hospitals in England and Wales is presented. Epidemic strains EMRSA-15 and EMRSA-16 are becoming endemic in hospitals in the United Kingdom, and theory predicts that EMRSA-15 and EMRSA-16 will reach respective endemic levels of 158 (95% confidence interval [CI], 143-173) and 116 (95% CI, 109-123) affected hospitals with stochastic fluctuations of up to 30 hospitals in each case. An epidemic of VRE is still at an early stage, and the incidence of hospitals newly affected by VRE is growing exponentially at a rate r=0.51/year (95% CI, 0.48-0.54). The likely impact of introducing surveillance policies if action is taken sufficiently early is estimated. Finally, the role of heterogeneity in hospital size is considered: "Super-spreader hospitals" may increase transmission by 40%-132% above the expected mean.