Think that's a spider bite on your arm? Think again. It could be methicillin-resistant Staphylococcus aureus, or MRSA, a type of staph infection increasingly seen in communities across the nation that is resistant to antibiotics most commonly used to treat skin infections.
UCLA researchers report in the Aug. 17 issue of The New England Journal of Medicine that MRSA is the most common cause of skin and soft-tissue infections among patients presenting in emergency rooms across the country. MRSA is resistant to the antibiotics used for years to treat these skin conditions, such as cephalexin and dicloxacillin.
"The study points to the rising prevalence of this type of MRSA and the need for clinicians to culture infections and make sure the proper antibiotic is administered to treat MRSA," said Dr. Gregory J. Moran, the study's principal investigator and a clinical professor of medicine in the department of emergency medicine and the Division of Infectious Diseases at Olive View–UCLA Medical Center.
Since the 1960s, MRSA has been found in health care settings, generally among patients who have been hospitalized or are in nursing homes. In the last few years, however, a new type of MRSA has emerged, affecting people with no connection to health care settings. Outbreaks of these new strains of MRSA have been reported among athletes, correctional facility inmates and military recruits. Still, the UCLA study demonstrates that the infections appear to be common in people who are not connected to any particular risk group.
"We noticed more patients showing up in our emergency room with infections that turned out to be community-associated MRSA and wanted to see if this was the case nationwide," said Dr. David Talan, an author of the study and a professor of medicine in the Division of Infectious Diseases and chief of the department of emergency medicine at Olive View–UCLA Medical Center.
Community-associated MRSA most often manifests itself on the skin as a boil or pimple that can be swollen, red and painful, and have discharge.
Researchers cultured the acute skin or soft-tissue infections of 422 patients seen at 11 metropolitan emergency rooms in the United States during August 2004.
Out of those patients, 249, or 59 percent, were found to have MRSA. The proportion of infections caused by MRSA in various cities ranged from 15 to 74 percent.
Further characterization of the MRSA samples, performed at the Centers for Disease Control and Prevention, revealed that one genetic type accounted for 97 percent of the samples.
"This one genetic type of MRSA is appearing in metropolitan areas across the country," Moran said. "More research will determine how prevalent it is in other parts of the nation."
Researchers tested the antibiotic resistance of the isolated MRSA samples and found that in 57 percent of cases, doctors had prescribed an antibiotic to which the bacteria were resistant.
"Doctors need to change what they've done for decades, since traditional antibiotics don't work against MRSA," Talan said. "We encourage physicians to reconsider antibiotic choices for skin and soft-tissue infections in areas where MRSA is prevalent in the community."
Talan notes that most MRSA cases are mild, and having the infection drained and keeping it clean resolves the problem. But when antibiotics are needed, it's important to prescribe an effective medication. Sometimes these infections may require hospitalization and, in rare cases, may even be life-threatening.
"It's important for us to identify and properly treat MRSA in order to halt further progression of serious infections and to prevent recurrence," Moran said.
Researchers tested the effectiveness of different types of antibiotics on the MRSA samples and found that 95 percent were susceptible to clindamycin, 6 percent to erythromycin, 60 percent to fluoroquinolones, 100 percent to rifampin and trimethoprim-sulfamethoxazole, and 92 percent to tetracycline.
The next step, according to Moran, is to compare these different antibiotics in real patients in order to identify an optimal treatment.
The study revealed several potential risk factors for community-associated MRSA. Patients with MRSA were more likely to report a spider bite as the reason for the skin lesion, perhaps thinking it was a bite in absence of other skin problems. Those with MRSA also were more likely to have close contact with a person with a similar infection.
"However, none of these risk factors were consistent enough to help doctors identify cases of MRSA -- it appears now that everyone is at risk," Moran said. "So if you think you have a spider bite or other type of skin lesion that is not healing, you want to see your doctor to make sure it's not an infection like MRSA."
Dr. Rachel J. Gorwitz, an author of the study and a medical epidemiologist at the Centers for Disease Control and Prevention, noted the importance of educating patients in order to avoid transmission. She offered the following guidance:
For more information, please visit the Centers for Disease Control and Prevention Web site at http://www.cdc.gov/ncidod/dhqp/ar_mrsa_ca_public.html.
Emergency rooms in the following cities were involved in the research: Albuquerque, N.M.; Atlanta, Ga.; Charlotte, N.C.; Kansas City, Mo.; Los Angeles, Calif.; Minneapolis, Minn.; New Orleans, La.; New York, N.Y.; Philadelphia, Pa.; Phoenix, Ariz.; and Portland, Ore.
The Centers for Disease Control and Prevention funded the study.
Other study authors include: Anusha Krishnadasan, Ph.D., from the department of emergency medicine at Olive View–UCLA Medical Center; Gregory E. Fosheim, M.P.H., Linda K. McDougal, M.S., and Roberta B. Carey, Ph.D., from the Division of Healthcare Quality Promotion at the National Center for Infectious Diseases of the Centers for Disease Control and Prevention in Atlanta, Ga.
Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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