WEDNESDAY, Aug. 16, 2006 (HealthDay News) -- In emergency rooms across the United States, a tough-to-treat staphylococcus bug is now the leading cause of skin and soft-tissue infections, a new study finds.
Methicillin-resistant Staphylococcus aureus (MRSA) is resistant to many standard antibiotics that have been used for years, but it can still be effectively treated with one of several antibiotics, experts say.
"MRSA is now the most common cause of skin infections in most of the big U.S. cities," said researcher Dr. Gregory Moran, a professor of medicine at the University of California, Los Angeles, David Geffen School of Medicine. "When doctors are deciding if a patient needs antibiotics, they should be given them antibiotics that cover MRSA. That's a change from things we've been doing for a decade. This has changed. A different type of bacteria is now the most common cause of infections."
The study is published in the Aug. 17 issue of the New England Journal of Medicine.
In the same issue of the journal, another study found that the antibiotic daptomycin is effective for treating bloodstream and heart infections caused by Staphylococcus aureus bacteria.
Based on this trial, the U.S. Food and Drug Administration has already approved the drug for use in these cases. Daptomycin has previously been approved for treating skin infections caused by S. aureus.
MRSA was, for a long time, limited to hospitals, nursing homes and other health care facilities. "It began to change several years ago," said Dr. Pascal James Imperato, distinguished service professor and chairman of the department of preventive medicine and community health, at SUNY (State University of New York) Downstate Medical Center in New York City. "We began to see it in people in the community who were not in hospitals."
The bacteria live uneventfully in the nose of many people but sometimes lead to serious infection. Symptoms can range from something as benign as an infected paper cut, to bloodstream infections, to infections of heart valves that can be fatal.
Community-associated MRSA most often appears on the skin as a boil or pimple that may be swollen, red and painful, and have a discharge.
Moran and his colleagues cultured skin or soft-tissue infections from 422 patients at emergency rooms in 11 cities across the United States.
"This was the first time that anyone did a broad slice across the whole U.S.," Moran said.
Of those 422 patients, 59 percent had MRSA. The prevalence of MRSA ranged from 15 percent to 74 percent, depending on the city.
One genetic type (USA300) accounted for 97 percent of the samples, and 74 percent were a single strain (USA300-0114).
"We weren't surprised that it was the most common bug overall," Moran said. "But we didn't know how uniform it was going to be, and all across the U.S., it was remarkably similar. There's something about this particular strain [USA300] that gives it some survival advantage over other types."
Almost all (98 percent) of the isolates had two toxins that make the germ more aggressive.
When tested, 95 percent of the MRSA samples could be treated with the antibiotic clindamycin, 6 percent with erythromycin, 60 percent with fluoroquinolones, 100 percent with rifampin and trimethoprim-sulfamethoxazole, and 92 percent with tetracycline.
But in 57 percent of cases, doctors had prescribed an antibiotic to which the bacteria were already resistant.
In the second trial, daptomycin was about as effective as standard therapy in treating patients. This trial was sponsored by Cubist Pharmaceuticals, which makes daptomycin.
"Daptomycin is an IV drug, so that's something that we would use for more serious infections that would need to be in the hospital," said Moran, who was not involved in this study. The infections studied were also not as uniform as the ones identified in the first study.
There are already several effective drugs for the type of skin and soft-tissue infections Moran studied. "Many of the drugs active against community strains of MRSA are older antibiotics that have been around for a long time," Moran said. "We don't really need to go with big, new, expensive antibiotics."
"Most infections occurring in the community are relatively mild and frequently resolve with very simple measures," Imperato added.
People can prevent infections by not sharing towels, razors or other common items, and by washing hands with soap and water, experts say.
Find out more about community-acquired MRSA at the U.S. Centers for Disease Control and Prevention.