Researchers have found a highly drug-resistant new strain of MRSA in the United States.
Sexually active gay men in San Francisco are 13 times more likely to be infected than the general population, researchers have found.
In the city's Castro district - where more gay people live than anywhere else in the United States, about one in 588 people are carrying the multi-drug resistant bug.
The strain is a new and harder-to-treat version of a recently identified form of MRSA known as USA300. Both are nastier versions of the methicillin resistant staphylococcus aureus (MRSA) commonly found in hospitals.
However, the USA300 sub-type identified in the gay community in San Francisco is resistant to many more front-line antibiotics.
USA300 is also prevalent among injecting drug users, and players of contact sports such as wrestling or American football.
The bacteria invade tissue under the skin, producing boils that can grow to the size of tennis balls. Severe cases can lead to fatal blood poisoning or a deadly flesh eating form of pneumonia that devours the lungs.
The USA300 strain was first identified in 1999 after it killed four young children in North Dakota. Since then it has become a serious problem in the United States, and researchers are worried it will spread.
PA