S.F. gay community an epicenter for new strain of virulent staph LETHAL NEW BACTERIA - S.F. AN EPICENTER NATIONAL PROBLEM: Contact with skin spreads virulent bug

Infection Rate by San Francisco ZIP Code. Chronicle Graphic Infection Rate by San Francisco ZIP Code. Chronicle Graphic Image 1 of / 5 Caption Close S.F. gay community an epicenter for new strain of virulent staph 1 / 5 Back to Gallery

A new variety of staph bacteria, highly resistant to antibiotics and possibly transmitted by sexual contact, is spreading among gay men in San Francisco, Boston, New York and Los Angeles, researchers reported Monday.

The study released online by the journal Annals of Internal Medicine found the highest concentrations of infection by the drug-resistant bug in and around San Francisco's Castro district and among patients who visit health clinics that treat HIV infections in gay men in San Francisco and Boston.

The culprit is a form of MRSA, or methicillin-resistant Staphylococcus aureus, a bug that was once confined to hospitalized patients but, since the late 1990s, has been circulating outside medical settings, afflicting anyone from injection-drug users to elementary school students. A strain called USA300 has been a leading cause of MRSA infection in this decade, and an exceptionally drug-resistant variant of it is now on the loose, researchers say.

The study estimated that 1 in 588 residents living within the Castro neighborhood 94114 ZIP code area is infected with that variant, which is resistant to six types of commonly used antibiotics. The risk of contracting this difficult-to-treat bug is 13 times greater for gay men than for the rest of the city's population, researchers found.

"We probably had it here first, and now it is spreading elsewhere," said Binh An Diep, a researcher at San Francisco General Hospital and lead author of the report. "This is a national problem, and San Francisco is at the epicenter."

The germ typically causes boils and other skin and soft-tissue infections and, despite its resistance to some drugs, is still treatable by surgical drainage and several classes of antibiotics. What is unusual in this case is the high percentage of infections - up to 40 percent - occurring in the buttocks and genitalia.

Although researchers have stopped short of declaring this form of staph a sexually transmitted disease, the infections are found where skin-to-skin contact occurs during sexual activity.

Most of the infections are limited to the skin surface, but the bacteria can invade deeper tissues or disseminate through the bloodstream. According to the federal Centers for Disease Control and Prevention, various forms of MRSA are causing 95,000 of these more costly and potentially life-threatening infections - and 19,000 deaths - annually in the United States.

Until last year, staph infections had never been linked to sexual activity. Early last year, New York City physicians traced three instances of staph infection apparently spread by sexual contact. Their report was published in February in the journal Clinical Infectious Diseases.

A month later, doctors from the Albany Medical Center in New York reported in the Journal of Urology three cases of multi-drug-resistant staph in the groins of three patients - one of whom developed a form of rapid-tissue destruction popularly known as "flesh-eating bacteria" disease. The patients recovered after treatments with surgery and antibiotics.

San Francisco General Hospital physicians have been battling an aggressive strain of MRSA, called USA300, since 2001. The most recent study estimates that this strain alone is infecting about 2,000 city residents a year.

But the latest problem is being caused by a new variant of USA300 that was first detected in a San Francisco patient in 2003. Among the six antibiotics it is resistant to are three that are normally considered for treatment of suspected MRSA. The study estimated that 200 cases of this highly drug-resistant variant are turning up in San Francisco each year, mostly among gay men.

"We are nowhere near the peak," Diep said. "The peak will occur when it spreads into the general population."

Diep said there is reason to believe that the more drug-resistant strain will make that leap because it is just a slight variant of USA300, which became one of the most common strains of MRSA in the United States only a few years after it was first detected.

The latest study focuses on the spread of the more drug-resistant strain in San Francisco and Boston, but reports of the bug are turning up in New York and Los Angeles.

Just why the new, more drug-resistant variety is concentrated among gay men is not yet known. Patients infected with HIV appear to run a higher risk of infection, but the study suggests that gay men are being infected with the staph germ regardless of whether they are HIV-positive.

One factor that could be in play is a medical history of heavy use of antibiotics, which creates conditions for breeding drug-resistant strains. Any patient, HIV-positive or not, who has had high previous exposure to antibiotics might be more susceptible.

The good news is that, once the public is aware of the risk, there are ways to prevent the spread of drug-resistant staph. It can be as simple as soap and water.

"Taking a shower after sexual contact may minimize contamination," said Dr. Chip Chambers, director of infectious diseases at San Francisco General, a co-author of the study. "Ordinary soap will do. It dilutes the concentration of bacteria. You don't need antibacterial soap."

Chambers stressed that some people, no matter how fastidious, could be more prone than others to staph infections. They could have unknown genetic traits or a history of antibiotic use that raises the risk.

"Despite one's best efforts, it is still possible, of course, to get a staph infection," he said. "This is why if one has a cut or open wound that it is important to clean it out and keep it clean."

The new variant of USA300 is resistant to the antibiotics erythromycin, clindamycin, tetracycline, Cipro-like antibiotics and drugs in the penicillin family. It also does not respond to mupirocin - a gel that is often used to kill MRSA growing in people's noses.

That still leaves a variety of antibiotics that will kill the new USA300 strain, but they tend to be more expensive and require intravenous drips. One common oral antibiotic, Bactrim, is still effective against it.

Chambers also pointed out that researchers at San Francisco General have shown that many skin sores and boils caused even by these drug-resistant strains of staph often can be treated without any antibiotics, just by surgical drainage of pus.

One of the paradoxes of bacterial infections is that using antibiotics to treat them is one of the quickest ways to promote antibiotic resistance. Although the drugs sometimes are essential, overuse is weakening their effectiveness worldwide.

Online resources

Learn about MRSA and MRSA prevention at:

links.sfgate.com/ZCBT

links.sfgate.com/ZCBQ

Online resourcesLearn about MRSA and MRSA prevention at:links.sfgate.com/ZCBT or links.sfgate.com/ZCBQ