Serosorting leads
to decreases in HIV rates in San Francisco

Gay men who seek sex partners with the same HIV serostatus as themselves--dubbed "serosorting"--are helping to reduce the HIV infection rate among men who have sex with men in San Francisco, reports the San Francisco Chronicle. The HIV incidence rate among gay and bisexual men in the city has dropped by nearly half over the last four years, according to the Centers for Disease Control and Prevention, with serosorting playing a key role in its decline. The annual HIV incidence rate was determined to be 1.2%, down from an estimated 2.2% four years ago.

"Serosorting is happening. It's working. It's one of the explanations we have for the flattening of the [HIV] seroincidence curve," Mitch Katz, public-health director, told the Chronicle.

Health officials say that successful antiretroviral therapy also may be contributing to the decline in the HIV infection rate among gay men, because HIV-positive adults with well-controlled infections are less likely to infect others through unprotected sex.

Because serosorting is becoming more common among gay men, researchers are beginning to study whether it puts those infected with HIV at risk of acquiring additional strains of HIV from their HIV-positive sex partners. Researchers at the University of California, San Francisco's Gladstone Institute of Virology and Immunology are analyzing data from the Positive Partners Study, started five years ago, to gauge whether HIV superinfection is happening and, if so, at what rate. Preliminary data show that four of the study's 176 participants have shown signs of superinfection. (Advocate.com)