I had unprotected sex one time with a man. Now I fear the worst. He refused to tell me if he is infected or not. Is it the law that he has to inform me if he is infected? (I live in the state of Michigan.) Can I get HIV from one contact?

K.F.

Let me answer the simple part of your question first. Yes, a person can become infected with HIV from a single act of sexual intercourse. The exact rate of transmission per sexual act is not known, but it is low. A few relevant medical-research studies have looked at the effectiveness of latex condoms in the prevention of HIV. In the couples who reported always using a condom, the risk of transmission from an infected partner to an uninfected partner was between zero and 2 percent in two years. In the couples who did not use condoms, the risk of transmission was between 10 and 12 percent in two years. Because this was over two years, the risk of a single act was very low, probably less than 1 in 200. In other words, your risk of contracting HIV from that one episode would be low, even if you knew for a fact that your partner had HIV, which you do not.

In most states, it is against the law to have sexual relations without informing the partner that you are HIV-positive. In some states, it is permissible for a physician or social worker to notify the patient's sexual or needle-sharing partners about the person's HIV positivity. In other states, unfortunately, a physician is not allowed to do so.

While I am not a lawyer, it appears that in Michigan, the health department is supposed to interview all people who test positive for HIV, ask them to name current and past sex partners, and assist in notifying the partners. To learn more, visit the Michigan legislature website. As far as you are concerned, however, what the law states does not really matter. You would not be notified if your partner had never been tested, if he tested positive but did not name you as a partner, or if the public health center could not reach you for some reason.

The simple thing for you to do is get an HIV test. If you had sex with the man more than six months ago, then the test results will be very accurate. A negative test will mean you do not need to worry about this any more.