Young women who initiate sexual intercourse at an early age are more likely than those with later sexual debuts to become infected with human papillomavirus (HPV) in part because of certain behavioral factors and partner characteristics, according to a longitudinal cohort study of American female college students.1 The factors and characteristics that influence the association between age at first sex and HPV infection include number of sexual partners in the previous six months, history of sexual transmitted infection (STI), alcohol and drug use related to sexual behaviors and partner's number of sexual partners.
Past research suggests that early sexual initiation is significantly associated with HPV infection. To determine the factors that are responsible for this association, researchers recruited a cohort of female first- and second-year students from a state university. To be eligible for the study, the women had to be sexually active, not pregnant or planning to become pregnant in the next three years and without a history of cervical biopsy or treatment for cervical intraepithelial lesions. Participants completed a survey and were tested for HPV at baseline; women returned for testing and completed another questionnaire every six months for up to three years. The survey asked women about their socioeconomic and demographic characteristics, sexual history, alcohol and drug use related to sexual behaviors (for example, contraceptive use when drinking or using drugs), and partner's socioeconomic, demographic and behavioral characteristics.
Researchers matched each participant who tested positive for HPV during the study with a participant of the same age who was not infected. Overall, 252 pairs of women were included in the analyses. Univariate analysis was used to determine the factors associated with early initiation of sexual intercourse and with HPV infection. Generalized estimating equation regression modeling was utilized to investigate which behaviors and characteristics mediate the association between age at first sex and HPV infection.
Of the sample, 59% were white, 12% black, 13% Hispanic, 9% Asian and 7% members of other racial or ethnic groups. On average, the participants were 20 years old and had first had intercourse at age 17. The mean lifetime number of sexual partners was four, and the mean number of partners in the previous six months was one. Twenty-nine percent of participants reported rarely or never using condoms, 16% sometimes using condoms and 52% using condoms most of the time; 10% reported having had an STI other than HPV. The mean score of alcohol and drug use related to sexual behavior was 3.4 (on a nine-point scale), and the mean number of partners' sexual partners was three.
In univariate analyses, several factors were significantly associated with young age at first sex: having had more than one sexual partner in the past six months, using condoms sometimes, having a history of pregnancy, being a current smoker, and scoring one or more on the scale assessing alcohol and drug use related to sexual behavior. In addition, the more partners a woman's partner had had in his lifetime, the younger she was at first intercourse. Having a history of an STI was marginally significant.
Some of the risk variables and partner characteristics that were significantly associated with young age at first sex were also significantly associated with HPV infection (having had more than one sexual partner in the past six months, being a current smoker, scoring one or more on the scale assessing alcohol and drug use related to sexual behavior, and having a partners who had multiple partners). Factors that were significantly associated with HPV risk but not young age at first intercourse were having a higher frequency of vaginal intercourse, having a history of an STI and having an older or a black partner.
Results of a general estimating equation regression analysis determined that age at first sex was significantly associated with HPV infection (beta coefficient, -0.20; odds ratio, 0.82). However, the beta coefficient decreased by 20% (to -0.16; odds ratio, 0.85) when factors found to be significant in the univariate analyses were added to the model, indicating that these variables help account for the association between age at first sex and HPV infection. The investigators concluded that four factors mediate the association because they were significant (or nearly so) in univariate analysis and had independent effects on HPV risk: number of sexual partners in the past six months (odds ratio, 1.7), history of an STI (2.2), alcohol and drug use related to sexual behavior (19.1) and partner's number of sexual partners (1.1).
In light of their findings, the researchers suggest that providers "encourage adolescents who have not yet had sexual intercourse to postpone sexual initiation." They also comment that youth who had their first sexual experience at an early age would benefit from counseling that stresses "the importance of modifying sexual behaviors." The researchers note that the mediating factors they identified explain only part of the association between age at first intercourse and HPV risk; other factors, such as cervical maturity, are also likely to be responsible for the association.--J.Rosenberg
1. Kahn JA et al., Mediators of the association between age of first sexual intercourse and subsequent human papillomavirus infection, Pediatrics, 2002, 109(01), <http://www.pediatrics.org/cgi/content/full/109/1/e5>.