"The advent of powerful antiretroviral drugs has had unintended consequences," CDC researcher Dr. Waimar Tun told the 15th International AIDS Conference in Bangkok Monday. Researchers say the AIDS drugs have encouraged risky sexual behavior, as evidenced by a 17 percent jump in newly HIV-positive gay and bisexual US men from 1999 through 2002, compared with a 7 percent increase in men overall. The data, based on CDC's 29-state survey, contrasts with overall US AIDS diagnoses, which increased slightly in 2002 after declining nearly 50 percent from the 1993 peak of 80,010 cases.

Part of the increase may be due to complacency among gay and bisexual youths, said Dr. Jeffrey Parsons, an AIDS researcher at New York University who documented an increase in barebacking, or unprotected anal sex. "It's certainly true of young people who have never lived through going to their friends' funerals and seeing the physical ravages of AIDS. They don't think it's that big a deal," he said. "There's also a kind of 'safe sex burnout.' ...They've been so careful so long." Acknowledging its roots are complex, Parsons said barebacking could stem from sexual compulsion, loneliness, or a "desire for intimacy."

Another factor is the amount of multiple partners.  A 2003 University of Miami School of Medicine survey of gay and bisexual men in South Beach and Miami nightclubs found the men had an average 6.4 sex partners in the past year.