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394 Environmental Contamination of Nursing Home Common Areas is Associated with Transmission of Methicillin-Resistant Staphylococcus aureus (MRSA)

Sunday, April 3, 2011
Trinity Ballroom (Hilton Anatole)
Courtney Reynolds, MS , School of Social Ecology and Division of Infectious Diseases, University of California Irvine School of Medicine, Irvine, CA
Samantha Eells, MPH , Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, CA
Victor Quan, BA , Division of Infectious Diseases and Health Policy Research Institute, University of California, Irvine School of Medicine, Irvine, CA
Diane Kim, BS , Division of Infectious Diseases and Health Policy Research Institute, University of California, Irvine School of Medicine, Irvine, CA
Ellena Peterson, PhD , Department of Pathology and Laboratory Medicine, University of California School of Medicine, Irvine, CA
Loren Miller , Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, CA
Susan S. Huang, MD, MPH , Division of Infectious Diseases and Health Policy Research Institute, University of California, Irvine School of Medicine, Irvine, CA
Background: Nursing homes often have high prevalence of MRSA colonization, even surpassing that found in hospitals and ICUs. We previously found that MRSA point prevalence exceeded MRSA admission prevalence in nursing homes, suggesting that MRSA transmission frequently occurs. Sources of transmission in nursing homes may be different than in hospitals, and may include environmental contamination of shared common areas. We therefore evaluated whether environmental contamination of these areas was associated with MRSA transmission in nursing homes.

Objective: To assess whether higher levels of environmental contamination in nursing home common areas are associated with MRSA transmission, defined as nursing homes which have a substantially higher MRSA point prevalence compared to their MRSA admission prevalence.

Methods: Using data from an ongoing study of nursing homes in Orange County, California, we identified 10 nursing homes with evidence of high vs. low MRSA transmission, based upon comparisons of MRSA admission vs. point prevalence. We categorized these nursing homes into two groups (high vs. low transmission), and evaluated MRSA environmental contamination of high touch objects in common areas. We selected 10 types of objects, which were each swabbed 5 times on separate visits to all 10 nursing homes. Swabs were incubated in tryptic soy broth with 7% NaCl for 18-24 hours and tested for MRSA using selective media plates. To evaluate cleaning practices, we placed UV-visible marks on the same list of objects, 6 times per object at each nursing home. We returned the following day to evaluate whether these marks were removed by routine daily cleaning.

Results: We obtained 500 cultures of high touch objects and placed 600 UV-visible marks to assess common area cleaning. Overall, 16% (78 of 500) of objects from all nursing homes were MRSA positive. We found a higher proportion of MRSA positive objects in the high transmission vs. low transmission nursing home groups (20% vs. 10%, p=0.005). Cleaning mark removal was similar in both groups (21% vs. 23%, p=0.62), although marks were removed twice as often for flat vs. non-flat objects across all nursing homes (35% vs. 17%, p<0.001).  

Conclusions: MRSA environmental contamination of high touch objects in nursing home common areas is associated with potential MRSA transmission. Further research is needed to evaluate whether these environmental sources facilitate MRSA transmission and whether improved cleaning or other related practices may reduce MRSA transmission and prevalence in nursing homes.