Community-associated methicillin-resistant Staphylococcus aureus in Minnesota

Methicillin-resistant Staphylococcus aureus (MRSA) with onset in the community among persons without traditional risk factors for healthcare-associated (HA) MRSA was first reported to the Minnesota Department of Health (MDH) in 1996 and four pediatric deaths due to community-associated (CA) MRSA were reported during 1997--1999. Concern about the apparent changing epidemiology of MRSA and possible increased virulence of CA-MRSA prompted an investigation into these four deaths and also a retrospective study at a Minnesota Indian Health Service Hospital. To further study this phenomenon, an additional retrospective surveillance study was conducted at 10 hospitals throughout Minnesota. Information was collected on CA-MRSA patients and all available isolates were tested. Although all CA-MRSA isolates are resistant to beta-lactam antimicrobials, most MRSA infections in this population had been initially treated with these agents. A prospective sentinel site surveillance study was then conducted at 12 hospitals throughout Minnesota. This study collected information of both CA- and HA-MRSA cases and compared patient and isolate characteristics in both groups (case-case study). This study demonstrated that CA-MRSA patients and isolates differed from those of HA-MRSA and indicated that CA-MRSA had evolved separately from HA-MRSA, most likely due to the overuse of antimicrobials in the community. Additional characterization of CA-MRSA isolates also indicated the frequent presence of a gene that confers inducible resistance to macrolides. This has clinical treatment implications for CA-MRSA. The findings in Minnesota, as well as those of other investigators, indicate that the occurrence of MRSA in the general community has important public health and clinical implications.