A new, highly drug-resistant strain of MRSA, or methicillin-resistant Staphylococcus aureus, has moved outside hospitals and is now spreading among gay men, researchers reported Monday.

Some of the hardest hit areas are San Francisco, Boston, New York and Los Angeles, according to a San Francisco Chronicle report.

Click here to read the San Francisco Chronicle story.

In regards to San Francisco, the study found sexually active gay men are 13 times more likely to be infected than the general population.

"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, in a news release. "This is a national problem, and San Francisco is at the epicenter."

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.

According to the Centers for Disease Control and Prevention (CDC), MRSA is responsible for about 19,000 deaths annually in America — most of which occur in the hospital.

The findings appear online in the journal Annals of Internal Medicine.