Studies on multiple-resistant staphylococcus aureus. (IV). Difference in incidence of methicillin-resistant staphylococcus aureus (MRSA) among institutions, departments and specimens

The sensitivity to methicillin (DMPPC) and cefazolin (CEZ) of 378 strains of Staphylococcus aureus isolated in 12 institutions in the Tohoku district of Japan in 1987, was examined by a microbroth dilution method using the Dynatech MIC-2000. The incidence of methicillin-resistant strains (MIC≥12.5μg/ml) of S. aureus (MRSA) was 34.4%(130/378), and that of cefazolin-resistant strains (MIC≥12.5 μg/ml) 32.5%(123/378). Of 130 MRSA strains, 107 were resistant also to cefazolin. There was astatistically significant specimen-to-specimen difference in the incidence of MRS A, which was higher in aspirated sputum, blood and urine than in expectorated sputum, pus, otorrhea and throat swab. The incidence of MRSA among institutions was found to vary between 0% and 75%. This difference was statistically significant. MRSA incidence among institutions with more and those with less than 500 inpatients was 44.3% and 14.4%, respectively, the difference being again statistically significant. The incidence of MRSA among departments was found to vary between 12.1% and 75.0%. The incidence of MRSA in urology, neurosurgery and general surgery departments was higher than in otorhinolaryngology and respiratory departments. The above results suggest that the increase in the incidence of MRSA can, for the most part, be ascribed to hospital infection.