The Epidemiology of Methicillin-Resistant Staphylococcus aureus and Clostridium difficile in Community Hospitals
This thesis is an investigation of methicillin-resistant Staphylococcus aureus (MRSA) and Clostridium difficile in community hospitals in southern Ontario, Canada. The first part of this thesis presents the findings of two longitudinal studies that describe the epidemiology of MRSA and C. difficile contamination in the environment of four hospitals. Overall, the prevalence of MRSA and C. difficile contaminated surfaces ranged from 2.5%-11.8% and 2.4%-6.4%, respectively. The majority of MRSA isolates were identified as spa type 2/t002; however, spa type 539/t034, a livestock-associated (LA) MRSA strain, was identified on several surfaces in two hospitals. For C. difficile, various ribotypes were identified in the hospital environment, including internationally recognized ribotypes 027 and 078. Chair backs, hand rails, isolation carts, and sofas were high risk surfaces for MRSA contamination. Cork surfaces and surfaces located in rooms exposed to a C. difficile patient were at a higher risk for C. difficile contamination. The second part of this thesis describes the utility of the temporal scan statistic for detecting MRSA and C. difficile clusters in a community hospital, using historical microbiological data. Clusters were investigated using molecular techniques and hospital records. Temporal factors (e.g., month, season, year) associated with these two pathogens were investigated using regression models. Several MRSA and C. difficile clusters were concordant with outbreaks identified by the hospital. Based on typing data, potential MRSA and C. difficile outbreaks and transmission events were identified that were not recognized by hospital personnel. The identification of specific time periods with significantly increased MRSA or C. difficile rates may have been associated with particular administrative and health events. The identification of MRSA and C. difficile on different surfaces in the hospital environment demonstrates that protocols are required to ensure that these surfaces are adequately cleaned and disinfected. Furthermore, the identification of LA-MRSA strains in the environment requires additional surveillance. The incorporation of the temporal scan statistic and molecular typing to standard surveillance methodologies are valuable tools for hospital personnel to evaluate surveillance strategies, understand transmission events, and focus investigations to address increases in the rate of MRSA and C. difficile cases in the patient population.