Infections caused by methicillin resistant Staphylococcus aureus (MRSA) were originally identified only in hospital settings. But new strains of MRSA have emerged and are now an important cause of community acquired infection worldwide,1 and they often affect patients with no risk factors for acquiring a strain of hospital origin. A study just published estimates that 94 360 invasive MRSA infections occurred in the United States in 2005, primarily but not entirely related to health care.2 In the study's surveillance sample, 58.4% of cases were defined as having community onset (cases with a healthcare risk factor but with a culture obtained ≤48 hours after hospital admission) and 13.7% were community associated (meaning that they started outside hospital and were not associated with health care).

Many isolates of community acquired MRSA produce Panton-Valentine leucocidin (PVL), a toxin that is not detected in MRSA infections associated with health care. The toxin destroys leucocytes and causes extensive tissue necrosis. The prevalence of PVL positive community …