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Methicillin-Resistant Staphylococcal Colonization and Infection in a Long-Term Care Facility

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; and Victor L. Yu, MD
[+] Article, Author, and Disclosure Information

Presented in part at the 29th Interscience Conference on Antimicrobial Agents and Chemotherapy, 17-20 September 1989, in Houston, Texas.

Requests for Reprints: Robert R. Muder, MD, Infectious Disease Section, Veterans Affairs Medical Center, University Drive C, Pittsburgh, PA 15240.

Current Author Addresses: Drs. Muder and Yu, Ms. Brennen, Ms. Wagener, Mr. Vickers, Mr. Rihs, and Mr. Yee: Veterans Affairs Medical Center, University Drive C, Pittsburgh, PA 15240. Mr. Hancock: Centers for Disease Control, Building 5, Room 210, Atlanta, GA 30333.

Dr. Miller: Centers for Disease Control, Building 1, B341, COl, Atlanta, GA 30333.

Ann Intern Med. 1991;114(2):107-112. doi:10.7326/0003-4819-114-2-1-107
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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.





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