Significance of Nasal Carriage of Methicillin-Resistant Staphylococcus aureus (MRSA) by Medical Staff in Nosocomial Infection

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Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most important microorganisms in nosocomial infection. Healthy medical staff working in MRSA endemic wards are known to have MRSA in their nasal cavity, swabs, but the significance of their positive nasal swab cultures in infections among the patients has not been confirmed. The purpose of this study was to compare the antibiotic susceptibility and coagulase typing of strains isolated from the infected patients and from nasal swab cultures of medical staff working in ICU. Twenty-six nurses and 20 doctors working in ICU where MRSA was endemic were examined. Six nurses and 10 doctors gave positive nasal swab cultures for S. aureus, and 2 of the nurses' strain and 5 of the doctors' strains were methicillin-resistant. These strains were sensitive to IPM, GM, MINO and OFLX, while the strains clinically isolated from infected patients were resistant to these antibiotics. MRSA isolated from nasal swab cultures from medical staff developed marked resistance to IPM, GM, MINO, and OFLX by incubating with these drugs, whereas they remained sensitive to VCM when they were incubated in VCM-containing medium. Methicillin-sensitive S. aureus (MSSA) isolated from nasal swab cultures of medical staff became resistant to DMPPC, CMZ, in addition to IPM, GM, MINO, and OFLX, but these strains did not develop resistance to VCM. Resistance to these drugs developed by incubating with these drugs did not diminish by incubating in drug-free medium for 3 weeks. The patients infected by MRSA had been previously given several kinds of antibiotics, whereas the medical staff had not been exposed to any kind of antibiotics during the same period. (ABSTRACT TRUNCATED AT 250 WORDS)

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