Risk factors associated with cervical human papillomavirus infections: a case-control study.

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.