Methicillin-resistant staphylococcal colonization and infection in a long-term care facility 
 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 less than 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 less than 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.
