Clinical incidence of methicillin-resistant Staphylococcus aureus (MRSA) colonization or infection as a proxy measure for MRSA transmission in acute care hospitals.

Background. The incidence of methicillin‐resistant Staphylococcus aureus (MRSA) colonization or infection has been used as a proxy measure for MRSA transmission, but incidence calculations vary depending on whether active surveillance culture (ASC) data are included. Objective. To evaluate the relationship between incidences of MRSA colonization or infection calculated with and without ASCs in intensive care units and non–intensive care units. Setting. A Veterans Affairs medical center. Methods. From microbiology records, incidences of MRSA colonization or infection were calculated with and without ASC data. Correlation coefficients were calculated for the 2 measures, and Poisson regression was used to model temporal trends. A Poisson interaction model was used to test for differences in incidence trends modeled with and without ASCs. Results. The incidence of MRSA colonization or infection calculated with ASCs was 4.9 times higher than that calculated without ASCs. Correlation coefficients for incidences...