The more consistently that sexually active men and women use condoms, the lower their risk of becoming infected with herpes simplex virus type 2 (HSV-2).1 In a prospective cohort study among individuals at risk for infection, 6% became infected during an 18-month period. The risk of acquiring the virus decreased by almost 30% with each increase across three categories measuring how frequently condoms were used (during 0–25%, 25–75% and >75–100% of sexual acts). In contrast, the risk of acquiring herpes simplex virus type 1 (HSV-1) did not vary by pattern of condom use.

The men and women studied were participants in a U.S. trial of an HSV-2 vaccine subsequently found to be ineffective. The trial took place in 22 centers located in STI clinics. To be eligible, individuals had to be seronegative for both HSV-2 and HIV, and must have had at least four sexual partners or at least one STI in the past year. Participants provided demographic information and sexual history at baseline. Over the next 18 months, they made 11 visits, during which they gave blood samples for HSV testing, were asked about their sexual behavior (including condom use) and sexual partners since the last visit, received counseling about safer sexual behavior and were offered condoms. Associations between various factors and infection with HSV were assessed with Kaplan-Meier curves, log-rank tests, and bivariate and multivariate Cox regression models.

Analyses were based on 1,843 participants who were sexually active at some time during the study period. Three-quarters were men, and half were younger than 27. Almost two-thirds were white, nearly one-third were black and the rest were of other races or ethnicities. The majority of men (66%) and women (70%) were eligible for enrollment because they had had at least four sexual partners in the past year; the rest had had at least one STI (12% of men and 19% of women) or met both criteria (22% and 11%, respectively). One-third of participants were seronegative for HSV-1.

Participants' average level of sexual activity declined significantly during the study, from 2.2 sexual acts per week in the study's first quarter to 1.7 in its last quarter. The level of condom use also fell, from use during 49% of sexual acts to use during 43%, on average; the decline was mainly due to falling use among participants reporting no new partners. Condoms were used 0–25% of the time by 40% of participants, 25–75% of the time by 31% of participants and >75–100% of the time by 29% of participants; 12% of participants never used condoms, and 13% always did. The median number of new sexual partners during the study differed significantly among heterosexual men (three), men who had sex with men (seven) and women (two). In these subgroups, 15–17% of participants had at least one partner who had genital herpes.

During the study period, 6% of participants became infected with HSV-2. Men and women had a similar rate of infection (5.1–5.7 per 100 person-years), but blacks had a higher rate than whites (9.4 vs. 3.5 per 100 person-years). In multivariate analyses, the risk of HSV-2 infection was significantly higher among both women (hazard ratio, 1.8) and men who had sex with men (2.7) than among heterosexual men. Blacks' risk of acquiring the virus was almost four times that of whites' (3.8), and participants aged 27 or younger had more than half again the risk of their older counterparts (1.6). In addition, risk was roughly doubled among individuals who had a partner with genital herpes (2.3) and among individuals who had sex more than twice a week, on average (1.8).

At the extremes of the spectrum of condom use, 8% of never-users and 5% of always-users became infected with HSV-2. Infection occurred in 7% of participants using condoms 0–25% of the time, 5% of those using them 25–75% of the time and 5% of those using them >75–100% of the time. In multivariate analysis, with each one-category increase in condom use, participants' risk of infection fell by nearly one-third (hazard ratio, 0.7); moreover, the benefit was similar among men and women.

Among participants who were initially seronegative for HSV-1, 3% became infected with this virus during the study. Participants who had any new partners during the study had a risk of infection more than three times that of their counterparts with no new partners (hazard ratio, 3.2). Condom use was not associated with the risk of acquiring this virus, but analyses were limited because of the small number of participants who became infected.

Consistent condom use protects sexually active individuals against HSV-2 infection, the researchers contend, although protection is not perfect. (They add that the study did not assess whether participants used condoms correctly.) While antiviral therapy likely plays an important role in lowering the risk of transmission from a partner known to have genital herpes, "the use of condoms remains an important preventive strategy for sexually active persons who are at risk for HSV-2 infection," they conclude.

As recently as 2000, writes the author of an accompanying editorial, good evidence of the effectiveness of condoms for preventing genital herpes, as well as most other common STIs, was lacking; however, research in this area has since made notable gains, giving health care providers evidence to support their recommendations to use condoms.2 Although other interventions hold promise for reducing STI transmission, the editorialist notes, condoms are "the best proven currently available means" for lowering the risk of infection. "Clinicians should tell their at-risk patients that condoms can substantially reduce their risk for these diseases if they use them regularly," he recommends.

—S. London


1. Wald A et al., The relationship between condom use and herpes simplex virus acquisition, Annals of Internal Medicine, 2005, 143(10):707–713.

2. Hook EW III, An ounce of prevention, editorial, Annals of Internal Medicine, 2005, 143(10):751–752.