Strains of Staphylococcus aureus, commonly known as staph, that are resistant to the antibioitc methicillin strike fear into the hearts of public-health officials. While those strains first popped up in hospitals and other institutions, where antibiotics flow relatively freely, they have since started appearing more often in infections that are picked up in the outside world. For this study, researchers kept track of an outbreak of methicillin-resistant Staphylococcus aureus (MRSA) infections in people who came to a clinic at San Francisco General Hospital.

What the researchers wanted to know: How common is methicillin-resistant Staphylococcus aureus (MRSA) in soft-tissue infections?

What they did: San Francisco General Hospital has a clinic that specializes in soft-tissue infections, particularly for poor, inner-city San Franciscans, most of whom have no health insurance coverage. Many of the clinic's patients are homeless. For this study, they looked back at all 6,156 people who came to the clinic between mid-2000 and mid-2003; several hundred had cultures taken of their infections.

What they found: Of the patients from which something could be cultured, most had S. aureus, and most of those were resistant to methicillin. Sixty-two percent of the patients with MRSA were first-time patients at the clinic, so these weren't people who had been to the clinic before and picked up the resistant bacteria there. Over half of patients said that the infection came from injecting heroin. This is an alarmingly high rate of infection with MRSA, the authors say, and they don't know exactly what causes it. It could be because these patients have so many infections that warrant antibiotics—all those drugs provide perfect conditions for resistance to evolve‑then heroin use and poor living conditions help the resistant bacteria persist and spread. Antibiotics are also often prescribed when they're not necessary because doctors think it isn't worth spending the time it would take to convince someone they don't need antibiotics, the researchers write. And some antibiotics that are thought to be effective on these infections probably just make things worse.

What the study means to you: The writers say MRSA probably won't remain confined in this medically underserved group of patients: rather, this is likely the beginning of an epidemic. They call for more research on the best ways to prescribe antibiotics for MRSA infections in soft tissue. Bacteria that are resistant to antibiotics are harder to kill, especially if doctors don't realize right away that they're dealing with a resistant infection.

Caveats: This is a description of the infections at just one big-city clinic; conditions are probably different in other places and even in other cities.

Find out more: Information about MRSA from the U.S. Centers for Disease Control and Prevention: www.cdc.gov

Read the article: Young, D.M., et al. "An Epidemic of Methicillin-Resistant Staphylococcus aureus Soft Tissue Infections Among Medically Underserved Patients." Archives of Surgery. September 2004, Vol. 139, pp. 947-953.

Abstract online: http://archsurg.ama-assn.org