MRSA: Deadly Super Bug or Just Another Staph?

Abstract

Commenting on an article by Klevens et al in the Journal of the American Medical Association that described the incidence of invasive methicillin-resistant Staphylococcus aureus (MRSA) infections, an editorialist estimated that more patients died with invasive MRSA than died because of HIV/AIDS in the United States in 2005. Simultaneous reports of MRSA outbreaks among high school athletes and deaths in previously healthy children set off a media frenzy calling MRSA a deadly “super bug.” Certainly the emergency department (ED) would seem to be a good place to study the epidemiology of this new disease whose impact has been confused and sensationalized. In this issue of Annals, Pallin et al attempt to answer the question of whether MRSA infection is associated with more patients being treated in EDs with skin and soft tissue infections than in the past. We already know that the ecology of skin and soft tissue infections has changed dramatically. Our ED-based emerging infections surveillance network, EMERGEncy ID NET, reported that MRSA caused 59% of skin and soft tissue infections among 422 adults treated at 11 geographically diverse US EDs in August 2004. Almost all isolates were the newly recognized community-associated MRSA USA 300, which contained genes for Panton-Valentine leukocidin toxin and carried staphylococcal cassette chromosome (SCCmec) type IV. Before this millennium, MRSA was rarely found in communitypresenting infections. For example, we found no MRSA, either community-associated MRSA or the older health care–associated strain, in a bacteriologic study of 160 cutaneous abscesses among patients presenting to the ED from 1992 to 1994; methicillinsusceptible S aureus was the most common pathogen, found in 50%. Although community-associated MRSA now is recognized to cause more of patients’ skin and soft tissue infections, does it cause more people to have skin and soft tissue infections? In other words, has the emergence of community-associated MRSA resulted in an increased burden of disease, not just a change in the strain-specific cause? This is the question that Pallin et al attempted to answer. Epidemiology is about counting, and counting is affected by what, where, and how one counts. With increased awareness of