One-third of sexually active 15-18-year-olds have had more than one partner, either sequentially or concurrently, within the past 18 months, and these teenagers differ in important ways from their peers who have had only one partner during the same period.1 Furthermore, according to an analysis of data from the National Longitudinal Study of Adolescent Health, they are at greater risk for nonviral sexually transmitted diseases (STDs) than teenagers who have had a single recent partner: The odds of having an STD are more than doubled among those who have had sequential partners and nearly quadrupled among those who have had concurrent ones. These increases in risk, however, are statistically indistinguishable from each other.

The analysis included 4,707 participants in the first wave of the nationally representative survey who reported having had at least one heterosexual relationship in the previous 18 months. Using the reported dates of first and last intercourse with each partner during this interval, the analysts determined that 65% of these young people had had a single relationship, 21% sequential relationships and 14% concurrent ones. All three groups were similar with respect to gender distribution and average age (17 years). The proportion of young people reporting concurrent relationships was significantly smaller among whites and Hispanics (13% of each) than among blacks and members of other racial or ethnic groups (18%).

On average, teenagers reporting sequential relationships had had 2.5 partners in the previous 18 months, and those reporting concurrent relationships had had 3.0. All pairwise differences in the number of partners among these adolescents and those who had had a single partner were statistically significant. Likewise, the three groups differed from each other in their levels of condom use at most recent intercourse (58% among those with only one partner, 55% among those with sequential partners and 47% among those with concurrent partners) and in their confidence in their ability to use contraceptives (average scores, 10.8, 10.5 and 10.2, respectively, on a 15-point scale).

In other regards, the two groups reporting multiple partners differed from teenagers reporting one partner but not from each other: They were less likely to report use of a hormonal contraceptive at last intercourse (23-24% vs. 28%) and more likely to say they had regretted at least one sexual encounter because they had been drinking (27-31% vs. 14%).

Four percent of the sample reported having had a nonviral STD diagnosed in the past 12 months. The proportion was significantly lower among those who had had a single relationship (3%) than among those who had had sequential or concurrent partners (5% and 7%, respectively); the difference between the two groups with multiple partners was not statistically significant.

The analysts used logistic regression to identify factors that were independently associated with teenagers' nonviral STD risk. In a model that included relationship patterns but not number of partners, teenagers reporting sequential or concurrent relationships were at significantly greater risk for STDs than those reporting one relationship (odds ratios, 2.0 and 3.2, respectively); the risks for the two groups with multiple partners were not significantly different from each other. A second model, examining number of partners but not relationship patterns, showed that teenagers' STD risk increased by 36% for each additional partner they had had. Finally, when both relationship patterns and number of partners were included, the differential in STD risk between teenagers with one partner and those with sequential or concurrent partners increased slightly (odds ratios, 2.3 and 3.9, respectively), and the association with number of partners lost significance. Again, further analysis showed no difference in risk between those reporting sequential and concurrent partners.

Results for background and other behavioral factors were similar in all three analyses. Women and blacks were at elevated risk for these infections (odds ratios, 3.1 and 3.5, respectively, in the most comprehensive model), as were adolescents who had used a hormonal contraceptive at last intercourse (1.7). In addition, as young people's confidence in their ability to use contraceptives increased, their STD risk rose (1.1).

Given the limitations of the study, including its cross-sectional design and the possibility that relationship types were misclassified, the analysts acknowledge that "to establish a causal linkage between sexual relationship patterns and STDs, a prospective study designed specifically to gather relationship information up to diagnosis of STD is needed." Nevertheless, they conclude that the results show the importance of interventions that "openly discuss the risks of concurrent sexual relationships" and the role of other behavioral and social risk factors.--D. Hollander


1. Kelly SS et al., The role of sequential and concurrent sexual relationships in the risk of sexually transmitted diseases among adolescents, Journal of Adolescent Health, 2003, 32(4):296-305.