by Betsy Carpenter

About the author: Betsy Carpenter is a contributing editor for U.S. News & World Report.

Fifteen years ago, genital herpes had the sexually permissive in a panic. One in 10 adults was thought to be stricken with this ancient, incurable venereal disease and its accompanying blisters and sores. Suddenly, “free” sex seemed very costly; here was a consequence of a one-night stand that the pill couldn’t avert and penicillin couldn’t remedy. Then herpes seemed to vanish, eclipsed in the public’s mind by the swift, deadly rise of AIDS.

But the virus didn’t go away: It surged to create an epidemic. According to a study published in the October 1997 edition of the New England Journal of Medicine, since the late 1970s, the proportion of...