IN THE LAST DECADE, several studies showed a trend for adolescent girls having children with older men. 1–4 These findings conjured up images of exploitation and coercion by parasitic older men who were preying on underaged virgins. As a result of these studies, many states tightened up statutory rape laws, and in 1996 the federal welfare reform laws encouraged more aggressive enforcement of these laws. 5–6 Critics of this reaction were fearful that this would discourage pregnant teens from seeking prenatal care out of fear of retribution for their partner. Sexually transmitted disease (STD) researchers started to wonder if age differences among adolescent girls and their partners were associated with STDs as well.
Several hypotheses were posed. The biologic hypothesis is that older men may serve as the reservoir for younger girls. In the case of both chlamydia and gonorrhea, there is some evidence of this notion. National data for both STDs indicate that the highest-prevalence age group for girls is 15 to 19 years, while for men it is 19 to 24 years. 7 The behavioral hypothesis is that these girls are less likely to use condoms because they are forced to have sex, lack condom negotiation skills, or want to have a child with that partner. Because of differences in maturity, life experiences, financial resources, and even physical size, relationships between older men and younger girls are inherently unequal. 1
The Evolutionary Model of Life-History Strategies theory attempts to explain why age differences are likely to exist. It posits that what attracts men is not youth but features related to fertility and that women seek out men for their economic potential. 8 This theory states that the age difference is normal and helps propagate the species. So should we be worried, or is it just natural? We need to study the question well before we can say.
If older men are in fact the source of the young women's STDs, then public health interventions should focus on behavioral interventions to help girls protect themselves from getting infected by older partners (e.g., negotiation skills and self-esteem boosters, safer-sex and abstinence promotion), social support services for the young girls (e.g., rape counseling), or policy to prevent older men from infecting younger girls (e.g., targeted screening, more aggressive enforcement of statutory rape laws, and improved partner services programs).
Several studies have examined whether girls with older partners are at higher risk for STDs and have led to variable conclusions. 9–14 In this issue of Sexually Transmitted Diseases, Begley et al 9 report that pregnant adolescents with older-age partners were more likely to test positive for chlamydia. In a previous issue of the journal, 10 we reported no link between the age of the partner and a repeat infection with chlamydia. Differences in methodology may account for the differences in findings. There are at least four methodologic issues that need to be resolved in order to truly examine the causal relationship between partner age and STDs among adolescent girls.
What Age Difference Is Important?
The age difference that is considered important has not been established. While some studies have examined 5- and 10-year differences, other studies have examined 2- or 3-year differences. Neither of these age differences is optimal because smaller differences may be more important for younger girls and less important for older teens. Developmentally, young teens (i.e., aged 13–16 years) may be very different from older teens (i.e., aged 17–18 years) and therefore more sensitive to smaller differences in age. Perhaps the age difference considered should not be uniform but rather tailored for different developmental age groups.
Cross-Sectional Versus Cohort Methods
Many of the STDs are asymptomatic. Chlamydial infections in women, for example, often are detected through cross-sectional screening programs; therefore, most newly diagnosed cases probably represent prevalent rather than incident cases. Examining risk factors for a partner that may not have been the person who transmitted the infection can lead to spurious results. In epidemiologic terms, this error is called incidence-prevalence bias. The best way to examine this association is to conduct a cohort study, which can be costly and time-consuming. To date, only six studies 9–14 have examined the effect of partner age differences as a risk factor for STDs, and all but one study 10 have used a cross-sectional approach.
All Partners Need to Be Examined
Though rates based on national surveys have dropped, 40.8% of adolescents have had sex by the age of 16. 15 While the majority of teens report having only one partner, the 2001 data show that 14% had four or more partners. 15 Thus far, when teens report more than one partner, most studies have examined partner characteristics of only one of the partners (usually the main partner). This is a naïve approach, and since concurrency is a risk factor for STDs 16,17 and different partners may have very different characteristics, it is advisable to examine all the partners. To do this, special statistical techniques must be used such as hierarchical linear modeling. While these techniques can provide less-biased estimates of effect measures than simpler techniques such as logistic regression or linear regression, they are more difficult to conduct and to interpret. Thus far, only one of the published studies examining older-aged partners as a risk factor for STDs used these more complex techniques. 10
No Consistency of Findings
Most of the research in age differences has involved pregnancy as the outcome, and it is not clear that this can be extrapolated to STD as an outcome. In addition, most of the studies have used a select group of adolescent girls (some pregnant, some who are already infected with an STD, some from a specific ethnic group). Begley and colleagues used a prevalent infection with chlamydia as the outcome. We used recurrent chlamydia as the outcome. The discrepancy in findings may be attributable to the groups used, the outcomes studied, and the differences in study design.
Why Should We Care?
Adolescent girls are an especially vulnerable group and are now a population at risk for many STDS, including HIV. Because of this, we need to explore all potential risk factors they may have. Whether adolescent girls who have sex with older men are more at risk for STDs and pregnancy can still be debated. The only way to answer this research question is to use sound methodology that is designed to answer the research question.
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