A new, highly drug-resistant strain of the "flesh-eating" MRSA
bacteria is being spread among gay men in San Francisco and
Boston, researchers reported on Monday.
In a study published online by the journal Annals of Internal
Medicine, the bacteria seemed to be spread most easily through
anal intercourse but also through casual skin-to-skin contact and
touching contaminated surfaces.
The authors warned that unless microbiology laboratories were
able to identify the strain and doctors prescribed the proper
antibiotic therapy, the infection could soon spread among other
groups and become a wider threat.
The new strain seems to have "spread rapidly" in gay populations
in San Francisco and Boston, the researchers wrote, and "has the
potential for rapid, nationwide dissemination" among gay men.
The study was based on a review of medical records from
outpatient clinics in San Francisco and Boston and nine medical
centers in San Francisco.
The Castro district in San Francisco has the highest number of
gay residents in the country, according to the University of
California, San Francisco. One in 588 residents is infected with
the new multidrug-resistant MRSA strain, the study found. That
compares with 1 in 3,800 people in San Francisco, according to
statistical analyses based on ZIP codes.
A separate part of the study found that gay men in San Francisco
were about 13 times more likely to be infected than other people
in the city.
The San Francisco researchers suggested that scrubbing with soap
and water might be the most effective way to stop skin-to-skin
transmission, particularly after sexual activities.
MRSA, for methicillin-resistant Staphylococcus aureus, was once
spread chiefly in hospitals. But in recent years, a number of
healthy people have acquired it outside hospitals.
Nearly 19,000 people died in the United States from MRSA
infections in 2005, the Centers for Disease Control and
Prevention has reported.
The infection can cause unusually severe problems, including
abscesses and skin ulcers. The bacteria can invade through the
skin to produce necrotizing fasciitis, giving them the popular
name of flesh-eating bacteria. They can also cause pneumonia,
damage the heart and produce widespread infection through the
Among gay men in the study, MRSA was spread by skin contact,
causing abscesses and infection in the buttocks and genital area.
The new strain is closely related to earlier ones. Both are known
as MRSA USA300.
The strain is much more difficult to treat because it is
resistant not just to methicillin, but also many more of the
antibiotics used to treat the earlier strains, said Dr. Henry F.
Chambers, an author of the new study.
The new strain contains a plasmid called pUSA03.
"This particular clone is resistant to at least three other
drugs, clindamycin, tetracycline and mupirocin," Dr. Chambers
said in a telephone interview.
Of the alternatives recommended by the C.D.C. and the Infectious
Diseases Society of America, trimethoprim-sulfamethoxazole
(Bactrim), clindamycin and a tetracycline, "this strain is
resistant to two of those three," he added. "In addition, the new
strain is resistant to mupirocin, which has been advocated for
eradicating the strain from carriers."