Risk Factors Associated with Cervical Human Papillomavirus Infections: A Case-Control Study

Abstract

As a part of the long-term prospective follow-up study conducted for women with genital human papillomavirus (HPV) infections in Kuopio University Hospital, Finland, since 1981, a case-control study was designed to assess risk factors for genital HPV infections. The cases (n = 691) were women who had been invited to attend the follow-up program on the basis of an abnormal cervical smear consistent with HPV-induced cytopathic changes, i.e., had a clinical HPV infection. The controls (n = 706) were a randomly selected group of women who had normal smears in the screening. Both groups were asked to fill in an extensive questionnaire focusing on detailed epidemiologic data on previous gynecologic and obstetric history, sexual practices, sexual partners, and smoking habits. In the multivariate analysis, eight variables emerged as independent risk factors for prevalent HPV infection. These variables could explain over 80% of the risk for infection. The risk for the infection varied with age, being highest in the age group 20-29 years, thereafter declining in the following 10-year age groups. The strongest independent risk factor was the number of sexual partners during the past 2 years (adjusted odds ratio = 12.1; 95% confidence interval 4.3-33.8 for five or more vs. one or no partners). Among the independent risk factors that increased the risk were also current smoking (adjusted odds ratio = 2.7; 95% confidence interval 1.7-4.3), warts in sexual partner(s) (adjusted odds ratio = 3.2; 95% confidence interval 1.6-6.5), and increasing frequency of sexual intercourse per week. Independent risk factors with a protective effect included a normal result in the last Papanicolaou smear, regular use of an intrauterine device as a contraceptive method, and good personal hygiene. No significant association between oral contraceptive use and risk for HPV infection was found. Condom use did not result in protection from the infection. The results of this study support the concepts that sexual intercourse is the main form of transmission among adults and that sexual promiscuity is the most important determinant for genital HPV infections.

Mediators of the Association Between Age of First Sexual Intercourse and Subsequent Human Papillomavirus Infection

“…Our analyses confirmed the findings of previous studies that demonstrated that age of first sexual intercourse is significantly associated with subsequent HPV infection, [13][14][15][16] but extended previous findings in that we specifically examined which risk behaviors and partner characteristics mediate the association between age of first sexual intercourse and subsequent HPV infection. As previously discussed, a risk behavior or partner characteristic acts as a mediator of the association between age of first sexual intercourse and HPV infection if age of first sexual intercourse is causally associated with the potential mediator and the potential mediator is causally associated with HPV infection.…”

“…A number of studies have demonstrated that sexual risk behaviors are associated with HPV infection, particularly with high oncogenic risk types. These behaviors include multiple 14,15,[32][33][34][35] Other risk behaviors that have been associated with HPV infection include smoking and alcohol use. 14,15 Black race has also been associated with HPV infection.…”

“…The variables were chosen on the basis of findings of previous studies. 2,[13][14][15][16][17][18]20,21 Sexual risk behaviors and associated outcomes included number of sexual partners during the past 6 months, frequency of vaginal intercourse during the past 6 months (per participant, averaged across all partners), condom use during the past 6 months, oral contraceptive use during the past 6 months, history of STI other than HPV, and history of pregnancy. Other risk behaviors assessed were current cigarette smoking, alcohol use as it relates to risky sexual behaviors, and drug use as it relates to risky sexual behaviors.…”

“…Recent studies have demonstrated that risk factors include number of sexual partners, partner's number of sexual partners, and early age of first sexual intercourse. 2,[13][14][15][16][17][18] Although several investigators have reported a significant association between early age of first sexual intercourse and subsequent HPV infection, the mechanisms by which early age of first sexual intercourse leads to HPV infection; ie, the mediators of the association, are unknown.…”

“…Recent studies have demonstrated that risk factors include number of sexual partners, partner's number of sexual partners, and early age of first sexual intercourse. 2,[13][14][15][16][17][18] Although several investigators have reported a significant association between early age of first sexual intercourse and subsequent HPV infection, the mechanisms by which early age of first sexual intercourse leads to HPV infection; ie, the mediators of the association, are unknown.Behavioral variables, biological variables, or both may play key roles in mediating the association between early age of first sexual intercourse and subsequent HPV infection. A behavioral or biological variable acts as a mediator of this association if early age of first sexual intercourse is causally associated with the mediating variable, which in turn is causally associated with HPV infection.…”