SAN FRANCISCO — While almost unheard of 10 years ago, community-associated methicillin-resistant Staphylococcus aureus has now become the single biggest cause of skin infections in the United States, Dr. Greg Moran said at the 12th International Conference on Emergency Medicine.
“We really don't know what's begun this sudden explosion of resistant staph in the community all over the United States, as well as in Canada and Europe,” said Dr. Moran, an emergency physician at the Olive View-UCLA Medical Center, Sylmar, Calif. “One thing we do know is that this is not a phenomenon of the hospital strains moving into the community. These are genetically distinct strains.”
In his 2006 study, virtually all the skin infections cultured from hospitals in 11 cities across the country were caused by community-associated strains; 78% of those were a single clone of USA300. “There is something about this strain that has given it a very, very strong survival advantage in the community,” Dr. Moran explained. “Almost all of [the skin infections] (98%) carried the Panton-Valentine leukocidin toxin gene and the SCCmec type IV gene.”
The SCCmec gene confers methicillin resistance, while the Panton-Valentine leukocidin toxin gene is associated with spontaneous skin and soft-tissue infections, as well as necrotizing pneumonia. Those mutations make the community-associated MRSA strains much more likely to cause infections than those MRSA strains found in hospitals, Dr. Moran said.
In addition to authoring a seminal paper on the topic (N. Engl. J. Med. 2006;355:666–74), Dr. Moran has kept track of the MRSA skin infections occurring in his own hospital since 1997. There were 25 cases documented that year. “That number rose to almost 450 per year in 2006 and 2007,” he said. “In 2001, 29% of our skin infections were MRSA. That more than doubled by 2003–2004, to 64%. In a very short time, we went from something we virtually never saw in the community, to it being the single largest cause of skin infections.”
Despite their prevalence, most of these infections are not serious and don't grow the “killer flesh-eating super bugs,” Dr. Moran said. “More than 90% of the isolates in our study were susceptible to at least one [antibiotic] agent.”
For most uncomplicated skin infections, he performs an incision and drainage, and he doesn't give antibiotics. “I do give antibiotics if there is a fever, significant associated cellulitis, immune or vascular compromise, if the lesion is in a high-risk area like the hands or face, or if the patient has already failed an incision and drainage,” Dr. Moran explained.