Laboratory and epidemiologic experience with methicillin-resistant Staphylococcus aureus in the USA.

Methicillin-resistant Staphylococcus aureus (MRSA) was a rare occurrence in US hospitals until the mid-1970s. Since that time outbreaks of MRSA infection have been reported in both large and small hospitals, in rehabilitation facilities, and in nursing homes. Transmission has been documented not only between hospitals, but between long-term care facilities and hospitals, and between the community and hospitals. Patient-to-patient spread within hospitals appears to result from transient colonization of the hands of health care workers, with colonized or infected patients being the intrahospital reservoir for the organisms. The best opportunity for control of outbreaks of MRSA infection within hospitals may depend on the rapid recognition of newly admitted patients who are colonized or infected. The laboratory plays a crucial role in this by providing prompt and accurate information indicating the presence of MRSA. Susceptibility test methods found to be most reliable for detecting MRSA in the USA include the broth microdilution MIC determination (performed in salt-supplemented broth), the Bauer-Kirby test with slight modification, or oxacillin-salt agar screening plates.