It was understood that, unless one of them was a beast, they would have sex. And they did, the night she arrived, after loosening up with Mexican food and Negro Modelos. The sex was good. So good they spent much of her six-day visit indoors.

Health officials may already know about this tryst. They have been lurking in chat rooms lately. It seems that meeting on the Internet and then taking it to the bedroom -- or wherever you like it -- has become a public health issue. Since August, when a syphilis outbreak was traced to an AOL chat room, there has been an astonishing revelation: You, too, can get a sexually transmitted disease if you have sex with someone you happen to meet online!

Cybercourtships and the resulting sexual entanglements are a budding field for researchers studying the spread of STDs. The feds have funded a study to understand the habits of horny Web users. Investigators in San Francisco have quizzed people coming to an STD clinic, and discovered that 17 percent have met a sex partner online in the last year.

The researchers also found that people who meet online wear condoms just as rarely as those who meet offline. (About 37 percent.) Gay men with Internet partners reported having receptive anal sex -- considered a more risky sexual behavior -- more often than gays who met their lovers offline. The researchers will present their findings next month at the International AIDS Conference in Durbin, South Africa.

"I do think that people with Internet partners do tend to be more risky than those who don't meet their partners over the Internet," says Andrea Kim, an epidemiologist in the San Francisco Department of Public Health HIV seroepidemiology unit who led the study.

Now, the U.S. Centers for Disease Control is getting in on the action. For the first time, the agency has funded a study -- done online, of course -- that seeks to unravel the mysteries of the Internet mating world. If you type "sex" in a search engine, along with sites boasting "Young and Tight Pussies" or the "Hottest Suck and Stroke Action" on the planet, you will also get Sexquiz.org. A humble survey will politely ask if you had anal sex with someone you met online, if you gave him a blow job or discussed your HIV status. Nine hundred people have filled out the survey since it was posted April 3. With 100 more (hurry up, folks), researchers will wrap it up and analyze the data.

"Epidemiology is studying patterns and distributions of diseases and that's what we're trying to understand: how the disease gets distributed through the medium of the Internet," says Sheana Bull, a medical sociologist at the Denver Public Health Department who is heading up the survey. She and the other researchers say they are not blaming the medium; they are just looking at it as a "newly emerging risk environment."

The Web site states its purpose up front, and even has a warning that sounds like a high school sex ed video. "If you have thought about or ever used the Internet to meet someone, and then had sex with that person, you might be at risk for getting infected with a sexually transmitted disease (STD) including HIV, the AIDS virus, or, if already infected, you may be able to pass an infection to another person."

The subtext here is that the Internet is a scary, devilish place. And maybe health officials have a point: If the ILOVEYOU virus can spread like crazy around the globe, why not an STD? Then again, once you're rolling around with a partner, does it matter whether you met in a chat room or a bar?

"It implies that there's this whole different group of people who live online and lurk there and, therefore, it would be different to have sex with them; either they would wash less, be more diseased, be more fiendish about hoping to pass on something disgusting to you, more violent, more pathological," says Pepper Schwartz, a sociology professor at the University of Washington and the author of numerous books on sex. "Whenever the circumstances are anonymous and you don't know them as a co-worker or through a friend, you always up your ante of a bad time."

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