Methicillin-resistant Staphylococcus aureus (MRSA), long a common and troubling source of nosocomial skin and soft-tissue infections, has made itself increasingly comfortable in the community and, even more troubling, has done so among individuals with none of its apparent risk factors. An increase in the number of community-acquired MRSA infections could radically alter the ways in which community-acquired S. aureus infections are treated because [beta]-lactam antibiotics are the agents typically given to treat them, and they aren't effective against methicillin-resistant strains. Researchers at the Centers for Disease Control and Prevention (CDC) examined population-based surveillance data and data from hospitals and laboratories to identify the scope of the problem.
The news isn't great.
Sorting through data from 11 hospitals in Baltimore, Maryland, that cover a population of 700,000; a "health district" in Atlanta that serves more than 3 million patients; and 12 laboratories in Minnesota, "representing [16%] of the licensed hospital beds in the state," the researchers identified more than 12,500 MRSA isolates. After weeding out those with risk factors for hospital-acquired MRSA, the rates of infection in the areas in which population-based data were collected (Atlanta and Baltimore) were roughly 26 per 100,000 and 18 per 100,000, respectively. Around 23% of the infections required hospitalization and 6% were classified as invasive. The most common dermatologic conditions seen were abscesses, cellulitis, folliculitis, and impetigo. Other invasive infections found were bacteremia, septic arthritis, and osteomyelitis.
In general, the results show that 8% to 20% of MRSA infections were most likely acquired in the community. The incidence of these was higher in Atlanta than in Baltimore, and in Atlanta, black race was a statistically significant risk factor. The authors conclude that "the choice of appropriate antimicrobial agents for suspected S. aureus infections of skin and soft tissue in patients in the community must now take into account the emergence of community-associated MRSA."
And it gets worse.
Serious dermatologic conditions, such as abscesses, furuncles, and cellulitis, are commonly seen in infections with S. aureus. Now scientists in Los Angeles have identified what is most likely an outbreak of necrotizing fasciitis stemming from community-acquired MRSA infection. Examining the records of 843 patients with wound cultures that were positive for MRSA during a 15-month period at the Harbor-UCLA Medical Center, researchers found that "14 were associated with cases of surgically confirmed necrotizing fasciitis." All 14 patients survived (pointing to the possibility of a less-virulent type of necrotizing fasciitis than is normally seen), although most (11) required "wide" or "radical" debridement, "often with incisions greater than 15 cm," and several underwent skin grafting.
Concomitant conditions or risk factors for necrotizing fasciitis were common, including injection drug use (past or current), seizure disorders, diabetes mellitus, and chronic hepatitis C infection, among others, although four patients had no known risk factors-a fact that worries the report's authors, who echo the authors of the CDC study in concluding that treatment for community-acquired necrotizing fasciitis "should include agents reliably active against the regional MRSA strain." Furthermore, because four of the case patients had no risk factors for MRSA, clinicians shouldn't automatically assume that MRSA isn't responsible for necrotizing fasciitis in the absence of such risk factors. -Doug Brandt
Fridkin SK, et al. N Engl J Med 2005;352(14): 1436-44;Miller LG, et al. N Engl J Med 2005;352(14):1445-53;Chambers HF. N Engl J Med 2005;352(14):1485-7.