Using condoms during sexual intercourse significantly decreases the likelihood that men infected with herpes simplex virus type 2 (HSV-2) will transmit the infection to their female partners, according to the first study to examine the effectiveness of condoms in preventing this infection.1Women are almost six times as likely as men to acquire HSV-2. Increased frequency of sexual intercourse, younger age and having a partner who is infected with both herpes simplex virus type 1 (HSV-1) and HSV-2 increase the likelihood of acquiring HSV-2. Although using condoms more than 25% of the time offers women a high degree of protection against acquiring HSV-2, men do not receive the same benefits.

To assess whether using condoms reduces the transmission of HSV-2, researchers analyzed behavioral and demographic data from participants in two multisite HSV vaccine trials conducted in the mid-1990s. The study included adults who, at enrollment, tested negative for both HSV-2 and HIV ("susceptible partners"), and had been involved in a monogamous relationship for at least six months with an individual infected with HSV-2 ("source partners"). Susceptible partners were interviewed during an initial screening, where they were instructed to keep a diary of their sexual activity for the duration of the study. The diary was to include number of sex acts, whether condoms were used during intercourse, the partner's use of antiviral medication, and number of new partners. The susceptible partners returned over the subsequent 18 months for routinely scheduled herpes testing.

Overall, 528 couples were included in the study. Of the susceptible partners, 267 were women and 261 were men, with a median age of 36 years. Ninety-two percent were white, and 98% were in a heterosexual relationship. Participants' median frequency of intercourse was twice weekly; half said that they had used condoms no more than 10% of the time since becoming sexually active. Of the source partners, 62% were seropositive for only HSV-2, while 38% were seropositive for both HSV-1 and HSV-2.

During the study's observation period, 31 (6%) of the 528 susceptible partners acquired HSV-2: 26 (10%) of the women and five (2%) of the men. Women acquired the virus at a rate of 8.9 per 10,000 sex acts--almost six times the rate of men (1.5 per 10,000 sex acts).

Using proportional hazards analyses stratified by gender and controlling for age, partner's serostatus and number of sex acts per week, the researchers investigated the influence of baseline characteristics on HSV-2 acquisition. They found that the susceptible partners' likelihood of acquiring the virus increased with each additional sex act per week (hazard ratio, 1.1) and each five-year reduction in age (1.6); the risk was doubled if the source partner was seropositive for both HSV-1 and HSV-2 (2.3). Participants who reported having used condoms more than 50% of the time throughout their lives were less likely to acquire the virus than those who reported less condom use (0.1).

The participants' mean frequency of sexual activity declined from 2.3 to 1.5 sex acts per week over the study's observation period. Condom use was low overall, with 61% of couples reporting ever using condoms. The use of condoms also declined throughout the study, from 27% to 21% of sex acts. Data on condom use were available for 22 people who acquired HSV-2 during the study; of these, 46% never used condoms, 36% used condoms for 1-25% of sex acts, 14% used condoms for 26-99% of sex acts and 5% always used condoms.

In a multivariate analysis of risks for HSV-2 acquisition during the study's observation period, controlling for age, condom use and number of sex acts per week, increased number of sex acts was again associated with an elevated risk of HSV-2 acquisition (hazard ratio, 1.2). Using condoms for more than 25% of sex acts was associated with a decreased risk of HSV-2 acquisition (0.3); however, when the data were analyzed by gender, condom use was highly protective for women (0.1) but had no significant effect for men.

The researchers note, "Our data indicate that condoms markedly reduce the risk of acquisition of HSV-2 in women, but not in men." They deduce that the reason for the difference may be that when used correctly, condoms fully cover the skin of the penis, from which the virus is shed, but do not protect men against exposure to all female genital sites from which the virus may be shed. The researchers point out that "contact with vulvar or perianal areas, the most common sites of viral shedding in women, may be a factor in the lower effectiveness of condoms in transmission from women to men." On the basis of their findings, the researchers estimate that more than 300,000 new cases of HSV-2 infection among women could be averted each year in the United States alone if condoms were used more consistently.--J. Rosenberg


1. Wald A et al., Effect of condoms on reducing the transmission of herpes simplex virus type 2 from men to women, Journal of the American Medical Association, 2001, 285(24):3100-3106.