Q: My husband is HIV positive, but he has told me that it is safe for us to have intercourse as long as he uses a condom. I would like to believe him, but a friend of mine became infected even though she said that her husband used condoms. How effective are condoms in preventing the spread of HIV infection?
A: Totally abstaining from sexual intercourse is, of course, the most certain way to avoid an HIV infection, and this obvious fact is behind the "Just say no!" advice trumpeted to unmarried young people. But this strategy is difficult to follow in a marriage.
While the level of effectiveness of using condoms in preventing the spread of HIV during intercourse is somewhat uncertain, a recent issue of the New England Journal of Medicine reported encouraging news. A European study followed 304 HIV negative subjects (196 women and 108 men), who had a stable heterosexual relationship with an HIV-positive partner, over an average period of 20 months. Among the 124 couples who used condoms consistently despite a total of about 15,000 episodes of intercourse, the authors reported no infection with HIV in the healthy partners. These results by no means prove that condoms provide absolute protection against HIV infection, but the study clearly shows that condoms, if always used during intercourse, are a very good line of defense.
By contrast, there was a significant rate of transmission of the infection among those couples who used condoms inconsistently. The story told by your friend and others, of getting infected despite the use of condoms, could well reflect uneven use.
Some couples may be lulled into a sense of false security because HIV transmission has not occurred over a significant period of time despite their failure to use condoms. They should be aware that the ease of transmitting HIV infection by the same individual varies over time because the amount of HIV virus in their blood may be different at any given time. The risk of becoming infected is greater during the later stages of the disease. Studies have also shown an increased risk of transmitting HIV if another sexually transmitted disease is present. In addition, male-to-female transmission is about twice as efficient as female-to-male transmission.
Dr. Margolis is professor of medicine and biological chemistry at the Johns Hopkins School of Medicine.