Robert R. Muder, MD; Carole Brennen, RN, MSN; Marilyn M. Wagener, MPH; Richard M. Vickers, BS; John D. Rihs, BS; Gary A. Hancock, BS; Ying C. Yee, MS; J. Michael Miller, PhD; Victor L. Yu, MD
Objective: To determine the natural history of colonization by methicillin-resistant Staphylococcus aureus (MRSA) among patients in a long-term care facility. We specifically sought to determine if MRSA colonization was predictive of subsequent infection.
Design: Cohort study.
Setting: Long-term Veterans Affairs Medical Center.
Patients: A total of 197 patients residing on two units were followed with regular surveillance cultures of the anterior nares.
Main Outcome Measurement: The development of staphylococcal infection.
Results: Thirty-two patients were persistent carriers of MRSA and 44 were persistent carriers of methicillin-susceptible strains (MSSA). Twenty-five percent of MRSA carriers had an episode of staphylococcal infection compared with 4% of MSSA carriers and 4.5% of non-carriers (P < 0.01; relative risk 3.8; 95% CI, 2.0 to 6.4). The rate of development of infection among MRSA carriers was 15% for every 100 days of carriage. Using logistic regression analysis, persistent MRSA carriage was the most significant predictor of infection (P < 0.001; odds ratio, 3.7). Seventy-three percent of all MRSA infections occurred among MRSA carriers. Isolates of MRSA from 7 patients were typed. Colonizing and infecting strains had the same phage type in all 7 patients and the same pattern of plasmid EcoRI restriction endonuclease fragments in 5 patients.
Conclusions: Colonization of the anterior nares by MRSA predicts the development of staphylococcal infection in long-term care patients; most infections arise from endogenously carried strains. Colonization by MRSA indicates a significantly greater risk for infection than does colonization by MSSA. The results offer a theoretic rationale for reduction in MRSA infections by interventions aimed at eliminating the carrier state.
Muder RR, Brennen C, Wagener MM, Vickers RM, Rihs JD, Hancock GA, et al. Methicillin-Resistant Staphylococcal Colonization and Infection in a Long-Term Care Facility. Ann Intern Med. ;114:107–112. doi: 10.7326/0003-4819-114-2-1-107
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Published: Ann Intern Med. 1991;114(2):107-112.
Geriatric Medicine, Infectious Disease.
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