Systematic Review of Measurement and Adjustment for Colonization Pressure in Studies of Methicillin-ResistantStaphylococcus aureus, Vancomycin-Resistant Enterococci, andClostridium difficileAcquisition

Abstract

Objective.Colonization pressure is an important infection control metric. The aim of this study was to describe the definition and measurement of and adjustment for colonization pressure in nosocomial-acquisition risk factor studies of methicillin-resistantStaphylococcus aureus(MRSA), vancomycin-resistant enterococci (VRE), andClostridium difficile.Methods.We performed a computerized search of studies of nosocomial MRSA, VRE, andC. difficileacquisition published before July 1, 2009, through MEDLINE. Studies were included if a study outcome was MRSA, VRE, orC. difficileacquisition; the authors identified risk factors associated with MRSA, VRE, orC. difficileacquisition; and the study measured colonization pressure.Results.The initial MEDLINE search yielded 505 articles. Sixty-six of these were identified as studies of nosocomial MRSA, VRE, orC. difficileacquisition; of these, 18 (27%) measured colonization pressure and were included in the final review. The definition of colonization pressure varied considerably between studies: the proportion of MRSA- or VRE-positive patients (5 studies), the proportion of MRSA- or VRE-positive patient-days (6 studies), or the total or mean number of MRSA-, VRE-, orC. difficile-positive patients or patient-days (7 studies) in the unit over periods of varying length. In 10 of 13 studies, colonization pressure was independently associated with MRSA, VRE, orC. difficileacquisition.Conclusion.There is a need for a simple and consistent method to quantify colonization pressure in both research and routine clinical care to accurately assess the effect of colonization pressure on cross-transmission of antibiotic-resistant bacteria.