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TABLE 1 DEFINITION OF TERMS Acute care facility: a facility (hospital) where lengths of stay average less than 30 days, and where a variety of services are provided, including surgery and intensive care. Carrier: an individual who is found to be persistently colonized (culture-positive for MRSA) at one or more body sites (eg, anterior nares, wound, perineum), but has no signs or symptoms of infection. Cohort: two or more patients colonized or infected with MRSA who are separated physically (eg, in a separate room or ward) from other patients who are not colonized or infected with MRSA. Cohort &al&g: the practice of assigning specified personnel to care only for patients known to be colonized or infected with MRSA. Such personnel would not participate in the care of patients who are culture-negative (or have not had cultures obtained) for MRSA. Colonized person: any person who is found to be culture-positive for MRSA, but has no signs or symptoms of infection caused by the organism. Decolonization therapy: topical and/or systemic antibiotic treatment administered for the purpose of eliminating MRSA carriage in an individual (note that intravenous vancomycin seldom eliminates MRSA carriage). Endemic: the usual (baseline) frequency of MRSA in an institution. The usual frequency, determined by ongoing surveillance, is not the same in all facilities. Epidemic: a definite increase in the incidence of MRSA above its expected endemic level of occurrence in a given facility. Incidence: the number of new cases of MRSA colonization or infection identified in a specified population during a given time period. Infected patient: a patient who has clinical or laboratory evidence of disease caused by MRSA (eg, bacteremia, pneumonia). MRSA: a strain of S aureus resistant to methicillin. Such strains also are resistant to oxacillin and nafcillin, cephalosporins, and imipenem. Nosocomial MRSA case: an individual who became colonized or infected with MRSA while in a healthcare facility. Nursing facility: a Health Care Financing Administration term used for nursing homes, long-term care facilities, and skilled nursing facilities where average lengths of stay exceed 30 days. Outbreak: a definite increase in the frequency of MRSA in a facility above the baseline level. In facilities where MRSA is uncommon, this may represent as few as two or three cases. In facilities where MRSA is common, an outbreak would represent a larger number of cases. Prevalence: the total number of persons with MRSA colonization or infection in a given population at a designated time. Staphylococcus aureus: a ubiquitous species of gram-positive bacteria found on the skin and in the anterior nares of most people. At any given time, 20% to 40% of adults are nasal carriers of S aureus, and up to 70% of the population carry S aureus in their nose at some time during their lifetimes.

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Our study suggests that there may be pervasive use of redundant antimicrobial therapy within US hospitals. Appropriate use of antimicrobials may reduce the risk of harm to patients and lower healthcare costs.

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