Gay and bisexual men who meet partners over the Internet are more likely to engage in risky sex but have a greater tendency to do so with people who have the same HIV status, a U.S. study said on Wednesday.

Forty-one percent of men who arranged to have sex with other men through the Internet reported having unprotected anal intercourse with their last partner, according to the Denver Public Health Department.

That compared with 31 percent of men who met partners in gay bathhouses, 29 percent who used other public sex venues and 25 percent of those who met in bars or at parties, according to data collected from a sexually transmitted disease clinic in Denver in 2003 and 2004.

The Colorado study also found that 51 percent of the men who used the Internet to meet had chosen a sex partner with the same HIV status as themselves, compared to 20 percent of bathhouse patrons.

Coupled with two other studies suggesting many HIV-positive gay and bisexual men are deciding to have sex based on viral load counts - the amount of HIV detectable in a person’s blood - the findings prompted warnings from health officials.

The studies were presented at the 2005 National HIV Prevention Conference in Atlanta on Wednesday.

“Many men who have sex with men may falsely believe that these strategies will protect them from HIV infection,” said Dr. Ronald Valdiserri, deputy director of HIV, STD and TB prevention programs at the Centers for Disease Control and Prevention.

Although choosing partners based on their HIV status or the amount of virus in blood can reduce the risk of acquiring or transmitting HIV, there are also dangers to doing so.

Many gay and bisexual men do not know they have HIV. And viral load results can become outdated and, even when accurate, are no guarantee that HIV is not present in some body fluids.

The practices can also expose people to other sexually transmitted diseases or put those who are HIV-positive at risk of becoming infected with another strain of the virus, otherwise known as a super-infection.

In the Denver study, the Internet users were more likely to have been diagnosed with gonorrhea.

The warnings came just two days after the CDC reported that more than 1 million Americans were living with HIV at the end of 2003.

Gay and bisexual men made up 45 percent of the estimated 1,039,000 to 1,185,000 people who are HIV-positive, making them the largest single infected risk group, said the Atlanta-based CDC.

AIDS, which destroys the immune system and leaves people vulnerable to opportunistic infections and cancers, has killed about a half million Americans and at least 22 million people worldwide since 1981.

Health experts have been warning of a possible resurgence of the epidemic, which eased in the early 1990s following the development of antiretroviral drugs. One of the factors fueling such concerns is the increased use of crystal methamphetamine, a powerful stimulant that can lower inhibitions and lead people to engage in risky behavior.

The number of gay and bisexual men who had used the illicit drug doubled between 2001 and 2004, according to a survey of more than 19,000 such men by the Los Angeles Gay and Lesbian Center. The jump was greater in those who were HIV-positive.