Men are more likely than women to have overlapping sexual relationships, and having concurrent sexual partners is associated with several risk factors for sexually transmitted diseases (STDs).1 In a survey of sexually active Seattle residents aged 18-39, 27% of men and 18% of women reported that during their most recent sexual relationship, they had had sex with at least one other partner. An increasing lifetime number of partners was significantly associated with an increasing likelihood of having concurrent sexual relationships for both women and men. Women who first had sex before age 16 and those who had an STD diagnosed during their most recent relationship, as well as men who had spent at least one night in jail, also had elevated odds of having concurrent partners.

Having multiple sexual partnerships is one of the most important risk factors for STD infection, and knowledge about concurrent partnerships is particularly crucial to an understanding of the dynamics of STD transmission. Yet such behavior is very difficult to study: Retrospective reporting may be biased by recall problems, and prospective reporting (through diaries, for example) is labor-intensive and may be incomplete. In addition, definitions of multiple partnerships vary, and many studies of sexual behavior have relied on special populations, such as STD clinic clients.

To gain a better understanding of multiple partnerships, researchers analyzed data collected in Seattle in February 1995. English-speaking Seattle residents aged 18-39 were contacted by telephone through random-digit dialing. Census blocks where blacks represented 40% or more of the population were oversampled, to ensure sufficient black respondents. Individuals who agreed to participate were asked about their demographic characteristics, their sexual history, their partners and the characteristics of those partners, and their STD history. The analyses are based on a sample of 637 sexually active men and women whose most recent partner was of the opposite sex.

Two measures of concurrency are included in the analyses. The first used answers to a straightforward question on how many people the respondent had had sex with while in his or her most recent relationship. Twenty-two percent of respondents reported concurrent recent partners--27% of men and 18% of women. For the second, the investigators combined information about the respondent with information that the respondent provided about his or her partner to assess whether the relationship had been mutually monogamous. Eighteen percent of women and 15% of men believed that their most recent partner had had other sexual partners during their relationship. When these responses were combined with the self-reports of concurrent partners, a total of 28% of respondents (31% of men and 26% of women) were in a relationship that had not been mutually monogamous.*

Chi-square analyses revealed that a number of personal characteristics were linked with respondents' reports that they had had concurrent partners. For example, a significantly higher proportion of divorced, separated or widowed men than of married men reported having had concurrent partners (37% vs. 15%). Among both men and women, lifetime number of partners was strongly associated with having sex with other partners: The proportion of men reporting recent concurrent partners rose from 13% among those with 1-3 lifetime partners to 52% among those with more than 15; for women, the proportion increased from 7% to 29%.

Reports of concurrent partnerships were far more common among men who had ever had a male partner (60%) than among those who had only ever had female partners (25%). Significant differences also were found between those who had had an STD at some point preceding their most recent relationship and those without such a history (41% vs. 23%), and between those who had ever spent a night in jail and others (44% vs. 20%). Finally, men who engaged only in vaginal intercourse reported concurrent partners less often than did those who engaged in a broader range of sexual activities (14% vs. 28-53%).

Among female respondents, the incidence of concurrent recent partnerships varied notably by age at first sexual experience. Thirty-four percent of women who first had sex before age 16 had been nonmonogamous during their most recent sexual relationship, compared with 11-14% of those who first had sex at later ages. Additionally, the proportion reporting concurrent partners was higher among women who had an STD diagnosed during their most recent relationship than among others (36% vs. 14%).

Overall, the proportion of respondents reporting that either they or their partner had been nonmonogamous was elevated among couples of different races, those who used condoms infrequently, those in which the respondent had had an STD diagnosed during the relationship or in which either partner had ever spent a night in jail, and those who had been together for a year or more. Age and educational differences, marital status and setting in which the couple met were not related to reports of concurrency. For almost all characteristics, the likelihood that either partner had been nonmonogamous rose steadily as the respondent's number of previous partners increased.

The investigators constructed three multivariate models to examine these associations while controlling for the effects of other factors: one each for men's individual characteristics, women's characteristics and partnership characteristics. Results of the first model revealed that the odds that a male respondent had had a concurrent sexual partner rose somewhat for every partner he had had over his lifetime (odds ratio, 1.2). Likewise, men who had spent at least one night in jail had significantly higher odds of having had a concurrent partner than men who had never spent a night in jail (2.0). No other factors were statistically significant among men, although respondents who reported ever having had a same-sex partner had marginally increased odds of having had a concurrent partner (odds ratio, 1.9; p=.09).

Lifetime number of sexual partners also significantly increased women's odds of reporting a concurrent sexual partner (odds ratio, 1.1). Other significant factors for women were having had an STD diagnosed while in their most recent relationship and having had first intercourse before age 16 (3.5 and 2.9, respectively).

Finally, relationships in which the respondent had had an STD diagnosed were more likely than others not to have been mutually monogamous (odds ratio, 2.7). Relationships that had lasted for at least six months were significantly more likely than shorter-lived ones to have included a concurrent partnership (2.4). Also, if either partner had spent a night in jail, the odds that their relationship was not mutually monogamous were significantly elevated (2.0). The odds of concurrency increased as the respondent's number of previous partners rose (1.1) and were elevated if the couple were of different races (1.7); married and cohabiting couples had reduced odds of being nonmonogamous (0.6).

The authors observe that "the frequency and correlates of concurrency varied strikingly by sex" and that "these differences may be due to real behavioral differences between men and women or to reporting differences." They speculate that "men may focus more on individual sex acts and thus recall more concurrent partners, whereas women may focus more on a relationship and neglect to report intermittent sexual encounters outside the context of an established relationship." However, they add that differences in men's and women's perceptions of social desirability may also drive variations in responses.

The investigators also note that the research had some important limitations. Notably, the examination of partnerships relied on a respondent's perception of whether his or her partner had had sex outside the relationship. In addition, no data were collected on how respondents characterized their partnerships in terms of commitment and intimacy. In conclusion, the researchers observe that "by increasing the accuracy of measures of both concurrent sex partnerships and the factors correlated with concurrency, we will be better equipped to tease out the role of concurrency in STD transmission dynamics."--M. Klitsch


1. Manhart LE et al., Sex partner concurrency: measurement, prevalence, and correlates among urban 18-39-year-olds, Sexually Transmitted Diseases, 2002, 2(3):133-143.