Sexually active gay men are many times more likely than others to acquire a new, highly drug-resistant strain of staph infection related to the MRSA bacteria that have caused havoc in many hospitals, finds a new study.

The new strain, known as MRSA USA300, is closely related to methicillin-resistant Staphylococcus aureus (MRSA), which has spread beyond hospital borders in recent years and caused outbreaks of severe skin and other infections in the general public.

But the newly discovered microbe is resistant to not only methicillin, but also to a many other normally effective, first-line antibiotics.

Like regular MRSA, the new multi-drug resistant microbe spreads easily through skin-to-skin contact, invading skin and tissue beneath the skin. While it can spread through casual skin-to-skin contact or even with contact with contaminated surfaces, the germ appears to be transmitted most easily through intimate sexual contact.

Scientists are concerned that it could soon gain ground in the general population, causing abscesses and ulcerations that can progress rapidly to life-threatening infections.

Dr. Binh Diep, PhD, a scientist at San Francisco General Hospital Medical Center and lead author of a report on the finding says his study found that up to 40 per cent of infections are occurring in the buttocks and genitalia, suggesting that the bug is spreading by sexual contact. 

If that can be confirmed, this would be the first recorded instance of certain staph being linked to sexual activity.

The research appears in the January 14 early online edition of the Annals of Internal Medicine.

A good scrubbing with soap and water, especially after sexual activities, may be the most effective way to prevent contact transmission, notes Diep.

Diep considers the rapid rise in infections alarming. About one in 588 people living in San Francisco's Castro district - a neighborhood with the highest number of gay residents in the country - are infected with the multi-drug resistant MRSA bacteria.

About one in 3,800 San Franciscans overall are infected - also a surprisingly high number, he says.

The scientists conclude that sexually active gay men in San Francisco are about 13 times more likely to be infected than the general population.

Diep believes that the new strain emerged in San Francisco first and is now spreading elsewhere.

"The potential widespread dissemination of multi-resistant form of USA300 into the general population is alarming," he says.

Until recently, MRSA bacteria were confined to hospitals, where extensive use of antibiotics has prompted highly resistant strains to evolve. The spread of MRSA into communities has led to heightened concern.

The scientists conclude that research should be undertaken to explore the link between MRSA and unsafe sexual risk behaviors.