  Nosocomial pathogens such as Methicillin-Resistant {\em Staphylococcus
aureus} (MRSA) and Vancomycin-resistant {\em Enterococci} (VRE) are the cause
of significant morbidity and mortality among hospital patients. It is important
to be able to assess the efficacy of control measures using data on patient
outcomes. In this paper we describe methods for analysing such data using
patient-level stochastic models which seek to describe the underlying
unobserved process of transmission. The methods are applied to detailed
longitudinal patient-level data on VRE from a study in a US hospital with eight
intensive care units (ICUs). The data comprise admission and discharge dates,
dates and results of screening tests, and dates during which precautionary
measures were in place for each patient during the study period. Results
include estimates of the efficacy of the control measures, the proportion of
unobserved patients colonized with VRE and the proportion of patients colonized
on admission.
