Increased research leads to dramatic declines.

Most people seriously underestimate the number of potential AIDS carriers they are exposed to with each additional sexual partner they have, according to research from Ohio State University. The risk of contracting the disease increases exponentially with each new sexual contact because an individual may be exposed to HIV--the AIDS virus--not only directly from his or her partner, but also from the partner's former partners (and their partners as well). Thus, someone who has had nine sexual partners, and each of them had an equal number of partners, has been exposed to 511 possible HIV carriers.

Just one-fourth of survey respondents correctly estimated or overestimated this number. The average estimate was that they would be exposed to 90 possible HIV carriers if they had sex with nine others. "This research clearly shows that people don't understand the woeful arithmetic of sexual promiscuity," notes Laura Brannon, co-author of the study and an assistant professor of psychology at the university's Lima campus. "Most people don't understand the exponential nature of the risk. This makes them feel more invulnerable to getting AIDS than they in fact are."

The sexual experience of the respondents varied from zero to more than 16 total partners. More than half said they had had four or fewer partners.

"It's time to start taking a good news slant on some of the STD [sexually transmitted diseases] trends," maintains H. Hunter Handsfield, professor of medicine, University of Washington, and director, STD Control Program, Seattle-King County Department of Public Health. There have been dramatic declines in gonorrhea, as well as drops in syphilis rates.

There also is reason for optimism on the research front, due to improved tests to screen for chlamydia. One is on the market and another is expected to be widely available shortly. The new tests require only a urine specimen, which will allow screening programs to be expanded greatly. Handsfield also is optimistic about the chances for success of an experimental vaccine to prevent genital herpes, currently being tested in clinical trials across the country.

However, "a very high proportion of people with STDs don't know they are infected," he points out. A majority of men and women with chlamydia have either no symptoms or such mild ones...