People with a partner who is known to be infected with gonorrhea or chlamydia have a lower risk of having either infection if they use condoms consistently than if they do not, according to an analysis of enrollment data from sexually transmitted disease (STD) clinic attendees participating in a multisite randomized controlled trial.1 Overall, the odds of infection were reduced by 20% if participants had used condoms consistently in the previous three months (odds ratio, 0.8). Among participants who had been informed that their partner had gonorrhea or chlamydia, the odds of infection were reduced by 60% if they reported having always used condoms in the previous three months (0.4).
The investigation aimed at addressing a common drawback of previous studies evaluating the protection offered by condoms against transmission of curable STDs—namely, they did not control for whether a participant's partner was infected. According to the researchers, people with partners who are infected, or who are perceived to be infected, may have an increased likelihood of condom use; hence, condom effectiveness may have been underestimated in studies that included people who had not been exposed to STDs. To assess the importance of accounting for a partner's infection status when investigating the effectiveness of condoms against chlamydia and gonorrhea, the researchers analyzed enrollment data from Project RESPECT—a trial of HIV counseling interventions conducted at five publicly funded STD clinics in four states (Maryland, New Jersey, Colorado and California) between 1993 and 1997. Participants were heterosexual, HIV-negative, aged 14 or older and English-speaking, and had been sexually active in the past three months. A total of 4,783 participants were tested for chlamydia and gonorrhea at study entry, and completed a questionnaire about their sexual behavior and condom use during vaginal and anal intercourse in the past three months.
Nine percent of participants (206 males and 223 females) had been referred to the clinic because they had received written or verbal notification from their partner or health department that the partner had chlamydia or gonorrhea. Of these, 48% tested positive for one or both infections. By comparison, of the participants who did not know their partner's infection status (2,470 males and 1,844 females), 25% tested positive for one or both infections.
In multivariate logistic regression analyses of data from both groups of participants that controlled for the total number of episodes of sex in the previous three months, consistent condom use was associated with significantly decreased odds of having chlamydia or gonorrhea (odds ratio, 0.8). Also, participants who had had a main partner were less likely than those who had not to have contracted one of these STDs (0.7). Odds of infection were doubled for males, blacks, participants aged 25 or younger, those with a high school education or less, and those who had been informed of their partner's infection status (1.7-2.2). Furthermore, participants who reported having had a new partner in the past three months were more likely than those who did not to be infected (1.3).
Analyses limited to participants with an infected partner showed that the odds of being infected with chlamydia or gonorrhea were lower among those who had always used condoms than among those who had not (odds ratio, 0.4), and higher among those who had had unprotected sex more than 10 times in the previous three months than among those who had not had unprotected sex (3.8). Although an analysis restricted to those who did not know their partner's infection status suggested that consistent condom use was related to a reduced likelihood of infection (0.8), this finding was not statistically significant. Finally, for participants who had had a new partner in the past three months and for those who perceived their partner to have a high risk of infection, consistent condom use was linked to having significantly reduced odds of being infected (0.7 for each).
The researchers comment that because of the likely overrepresentation of people who had experienced condom "failures" among the participants known to have an infected partner, the study provided "only a minimum estimate of condom effectiveness." Still, the analysts suggest that "consistent condom use likely provides greater protection against transmission of [gonorrhea and chlamydia] than previously reported, a finding that holds important implications for public health recommendations and practice."
—T. Lane
REFERENCE
1. Warner L et al., Condom effectiveness for reducing transmission of gonorrhea and chlamydia: the importance of assessing partner infection status, American Journal of Epidemiology, 2004, 159(3):242-251.