. . . But You Were Afraid to Ask

People across the U.S. rushed to call medical hot lines last week to find out the latest scientific information about the ways the AIDS virus can be transmitted. The number of inquiries was so great that the lines were often tied up for hours. Here are answers to some delicate questions about what can be risky and how people can protect themselves:

Q. Is kissing someone with AIDS dangerous?

A. A very small quantity of the AIDS virus can get into saliva. But it is < rapidly destroyed by the fluid's digestive enzymes. There has never been a documented case of HIV infection through saliva. So open-mouth kissing is considered a low-risk activity, but it is not absolutely safe.

Q. What kind of sex is most dangerous?

A. Being on the receiving end of anal intercourse carries the greatest risk, for heterosexuals as well as gays. Blood vessels in tissues lining the anus and rectum are easy to rupture, and that gives HIV a direct passageway to the bloodstream. The majority of sexually transmitted cases (as opposed to those from shared needles or transfusions) probably result from anal intercourse. Vaginal intercourse is less risky; oral sex has the least risk.

Q. Is the man or woman at greater risk in vaginal sex?

A. Women have higher odds of being infected by an HIV-positive man than the reverse. Infected semen can remain in the vagina and uterus for days. And the tissues of the vagina, though tougher than those in the anus, can also be torn during intercourse. A man, however, is exposed to vaginal secretions only during the sexual act itself. Unless he has genital ulcers or a cut on the penis, the chances of being infected are small.

Q. What is the best protection during intercourse?

A. Men should wear a lubricated latex condom. Most brands contain the spermicide nonoxynol-9, which also kills the AIDS virus. Lambskin condoms will not do the job since the virus can pass through the porous natural membrane.

Q. Does having sex during menstruation increase the risk of infection?

A. Studies suggest that the virus may pass more readily from woman to man during that time. A condom provides protection, but it is probably safer to abstain from vaginal intercourse during a period.

Q. How dangerous is oral sex?

A. Not as hazardous as intercourse, but nothing to be casual about. The partner performing oral sex is more at risk because he or she comes into contact with vaginal or seminal fluids. The virus can pass from those fluids into cuts in the mouth. Those receiving oral sex are exposed only to saliva.

Q. What precautions can be taken in oral sex?

A. Males receiving it should wear a latex condom. When the woman is the receiving partner, a dental dam should be used. That is a square piece of latex placed over the vaginal area. Many pharmacies now carry dams, a nonprescription item, on racks next to condoms.

< Q. At what point in a relationship is it reasonable to stop taking precautions against HIV infection?

A. Protection should be used for the first six months after starting a relationship with a new partner. Then each partner should be tested for HIV. If both test negative and the couple have a monogamous relationship and don't indulge in risky behavior, such as using needles, then it's safe to discontinue using condoms as a protection against AIDS.

Q. Is it risky to play sports or share athletic facilities with people who are infected?

A. The AIDS virus is not found in sweat. So health-club members need not worry about who last rode the exercise bike. But in contact sports where bloody injuries can occur -- such as boxing, football and basketball -- it's possible for the virus to pass from one athlete to another. The risk appears to be extremely small: the Olympics' chief medical officer said last week that Magic Johnson would be welcome to play in the 1992 Games.