EFFICIENT DETECTION AND LONG-TERM PERSISTENCE OF THE CARRIAGE OF METHICILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS

The natural history of the carriage of methicillin-resistant Staphyloc occus aureus (MRSA) was examined in a 9-year retrospective cohort stud y of 102 known carriers. The population studied consisted of patients admitted to a university hospital from 1989 through 1991; a review ext ending back to January 1983 was conducted. The focuses of the study in cluded the duration of carriage among patients who were known to have carried MRSA previously and who were readmitted to the hospital (36 pa tients) and the optimal anatomic site for screening (66 patients). Cul tures of the nares (sensitivity, 93%; negative predictive value, 95%) were considerably more valuable for the detection of MRSA colonization than were cultures of cutaneous sites of the axilla, groin, and perin eum (sensitivity, less than or equal to 39%; negative predictive value , less than or equal to 69%). The estimated half-life of MRSA coloniza tion in this special population of patients was similar to 40 months. Restriction enzyme analysis of plasmid types of paired isolates from t he 12 patients with MRSA carriage persisting for >12 months revealed f ive instances (42%) in which both isolates were of the same type. In s ummary, our results indicate that the majority of readmitted carriers harbor MRSA for >3 years and that, in this population, culture of the anterior nares alone (with culture of wound or sputum, when present) i s a valid and efficient method for the detection of persistent MRSA ca rriage.