Epidemiology and Clonality of Community-Acquired Methicillin-Resistant Staphylococcus Aureus in Minnesota, 1996???1998

EPIDEMIOLOGY AND CLONALITY OF COMMUNITY-ACQUIRED METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS IN MINNESOTA, 1996–1998 [Naimi TS et al. CID 2001;33:990]: The authors from the Minnesota Health Department, CDC, and Indian Health Service provide this review of community-acquired infections involving methicillin-resistant S. aureus in Minnesota from 1996–98. Cases were defined as MRSA infections in patients without any risk factors for this pathogen. The review indicated that 299/354 (84%) were skin and soft tissue infections, primarily skin abscesses and cellulitis; there were 13 cases of otitis, 12 of pneumonia, 12 cases of bursitis, 11 with bone and joint infections, and nine with bacteremia. Most of the patients were under the age of 30 years and most of the isolates were susceptible to clindamycin, ciprofloxacin, gentamycin, tetracycline, and trimethoprimsulfamethoxazole. Molecular subtyping by PFGE showed “striking” clonality in that over 80% of the isolates were clonally related. Of the 354 patients, 103 (29%) were hospitalized and 282 (84%) were initially treated with antibiotics that were not active in vitro, primarily betalactams. Comment. This is an important report on a subject of substantial current concern. The results are quite analogous to another recent report about community-acquired S. aureus infections involving MRSA that was community-acquired with clonally-related strains in a population served by the Indian Health Service in New Mexico. In both reviews, the MRSA infections occurred in patients without well defined risk factors for infections involving resistant microbes, most involved young adults, most involved strains that were clonally related, and the strains recovered were substantially different than nosocomial isolates of MRSA in showing sensitivity to multiple alternative antibiotics. Of particular interest in the Minnesota report was the observation that over 80% of the patients were treated with betalactam antibiotics that were inactive in vitro. This experience indicates the importance of microbiological studies as a guide to treatment of individual patients and the importance of studies of microbial epidemiology.