ATLANTA, Georgia (Reuters) -- A growing number of gay and bisexual men in the United States are engaging in risky sex with partners they meet on the Internet, raising fears that the AIDS virus could be poised for a major comeback in the group hardest hit by the epidemic.

Online chatrooms and Web sites are replacing gay bathhouses and sex clubs as the most popular meeting point to arrange high-risk sex, according to two new studies presented on Tuesday at the 2003 National HIV Prevention Conference.

The findings come amid growing evidence of an apparent resurgence of HIV, the virus that causes AIDS, as well as syphilis in men who have sex with men. The presence of sexually transmitted diseases is known to facilitate the spread of HIV.

More sexual encounters

New HIV diagnoses among gay and bisexual men have jumped more than 17 percent since 1999, the U.S. Centers for Disease Control and Prevention reported this week. Some 850,000 to 950,000 Americans have the AIDS virus and approximately 16,000 die from the disease each year.

"It's clear we need to reach gay and bisexual men with appropriate messages, not only in traditional high-risk settings but also online," said Dr. Ron Valdiserri, deputy director of the CDC's National Center for HIV, STD and TB Prevention.

In one survey by the California Department of Health Services, 23 percent of gay and bisexual men infected with syphilis admitted meeting sexual partners on the Internet, compared to 21 percent who had done so in bathhouses.

Researchers noted that men who met partners online, in bathhouses or at sex clubs tended to have more sexual encounters than those who did not.

Using the Web to educate

A separate study by the Center for AIDS Prevention Studies at the University of California in San Francisco found that 39 percent of gay and bisexual males interviewed online admitted having unprotected anal sex with someone they had met on the Internet in the previous two months.

Eleven percent of these respondents were HIV-positive.

Despite the sobering data, there were some signs the Internet could be used as a tool for delivering HIV prevention and safe sex messages to groups at high risk.

AIDS experts reported success raising HIV and STD prevention with gay and bisexual males online through the use of banner ads, one-on-one outreach sessions and discussions in chat rooms on Web sites.

The anonymity of the Internet often allowed educators to address issues some men might feel reluctant to discuss in clinics or elsewhere. There was also a need to heighten awareness of HIV prevention with other groups such as minorities and teen-agers.