Abstract
BACKGROUND: Cohort effects, new sex partnerships, and human papillomavirus (HPV) reactivation have been posited as explanations for the bimodal age-specific HPV prevalence observed in some populations; no studies have systematically evaluated the reasons for the lack of a second peak in the United States. METHODS: A cohort of 843 women aged 35-60 years were enrolled into a 2-year, semiannual follow-up study. Age-specific HPV prevalence was estimated in strata defined by a lower risk of prior infection (<5 self-reported lifetime sex partners) and a higher risk of prior infection (≥ 5 lifetime sex partners). The interaction between age and lifetime sex partners was tested using likelihood ratio statistics. Population attributable risk (PAR) was estimated using Levin's formula. RESULTS: The age-specific prevalence of 14 high-risk HPV genotypes (HR-HPV) declined with age among women with <5 lifetime sex partners but not among women with ≥ 5 lifetime sex partners (P = .01 for interaction). The PAR for HR-HPV due to ≥ 5 lifetime sex partners was higher among older women (87.2%), compared with younger women (28.0%). In contrast, the PAR associated with a new sex partner was 28% among women aged 35-49 years and 7.7% among women aged 50-60 years. CONCLUSIONS: A lower cumulative probability of HPV infection among women with a sexual debut before the sexual revolution may be masking an age-related increase in HPV reactivation in the United States.