Incidence, clearance and predictors of human papillomavirus infection in women.

Background: Persistent infection with carcinogenic human papillomavirus (HPV) is linked to high-grade lesions and cervical cancer. To better understand the natural history of HPV, we sought to determine the rates of incident and cleared carcinogenic HPV infection, by age, among women aged 15-49 years and to explore risk factors for incident infection.

Methods: Women enrolled in an earlier HPV prevalence survey (500 of 800 who were HPV-negative and all 121 who were HPV-positive) were invited to participate in follow-up HPV testing at their periodic health examination one year later. A cervical soft-brush specimen for HPV testing and a smear for cytologic examination were obtained, and participants completed a questionnaire on their demographic characteristics and sexual history.

Results: Two hundred and fifty-three (50.6%) previously HPV-negative women and 54 (44.6%) previously HPV-positive women were retested. The mean interval between visits was 14.0 (standard deviation 2.0, median 13.5, range 9.0-21.3) months. Incident HPV infection occurred in 11.1% (28/253) of the women overall, with the highest rate, 25.0% (6/24), in the 15-19-year age group. In the univariate analyses, risk factors for incident HPV were the median number of sexual partners in the past year (< or = 1 v. > or = 2: odds ratio [OR] 8.2, 95% confidence interval [CI] 3.0-22.2; p < 0.001) and the median number of sexual partners over a lifetime (> 3 v. < or = 3: OR 3.0, 95% CI 1.2-7.2; p = 0.014). In multivariate logistic regression modelling adjusted for age, median number of sexual partners in the past year, median number of sexual partners over a lifetime, marital status, current smoking and current use of oral contraceptives, only the median number of sexual partners in the past year remained significantly associated with incidence (OR 6.2, 95% CI 1.6-24.5; p = 0.009). Of the previously HPV-positive women, 51.9% (28/54) had cleared the infection.

Interpretation: Incident infection with carcinogenic HPV was highest in women aged 15-19 years, and risk factors were consistent with a sexually transmitted infection. A large proportion of the women who were HPV-positive appeared to have cleared the infection after one year.