title: A prospective study of absolute risk and determinants of human papillomavirus incidence among young women in Costa Rica.
abstract: BACKGROUND
  High risk human papillomaviruses (HR-HPV) are known to be extremely common, sexually transmitted infections, but more information is needed regarding the absolute risks of type-specific HR-HPV infections in the years following sexual debut.
  
  
  METHODS
  We conducted a survival analysis of 3,737 women aged 18-25 from the control group of the Costa Rican Vaccine trial to determine the absolute risks of HR-HPV infections at 12 months, 24 months, and end of follow-up (average of 50.7 months). To corroborate determinants of infection, we used Cox proportional hazards methods to assess associations between demographics and sexual risk behaviors and incident HR-HPV.
  
  
  RESULTS
  Cumulative incidence for HR-HPV infections was 51.3% at the end of the study period. The most common incident types were HPV52 (15.4%), HPV51 (13.6%), and HPV16 (12.4%). Type-specific cumulative incidence corresponded closely with type-specific prevalences, except that HPV16 was more prevalent than predicted by incidence, suggesting greater persistence. The strongest predictors of incident HR-HPV infections as a group in a multivariate analysis were the expected correlates of sexual behavior of the woman and her partner, such as being single (HR 1.6, 95% CI 1.4-1.8) or divorced/widowed (HR: 2.1, 95% CI: 1.7-2.7), having multiple HPV infections at enrollment (HR: 1.5, 95% CI: 1.3-1.7), and current smoking (HR: 1.2, 95% CI: 1.0-1.3). In women who reported being having only one lifetime sexual partner (being in a monogamous relationship), the strongest predictors of HR-HPV included not living with sex partner (HR: 2.1, 95% CI 1.7-2.5) and age of sex partner (HR: 1.4, 95% CI: 1.0-1.8).
  
  
  CONCLUSIONS
  We confirm the extremely high incidence of HR-HPV in young women, emphasizing the importance of vaccinating young girls before sexual debut.
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, DHHS, Bethesda, MD, USA. clarkma2@mail.nih.gov
authors.forename: Megan
authors.initials: M
authors.lastname: Clarke
authors.forename: Mark
authors.initials: M
authors.lastname: Schiffman
authors.forename: Sholom
authors.initials: S
authors.lastname: Wacholder
authors.forename: Ana Cecilia
authors.initials: AC
authors.lastname: Rodriguez
authors.forename: Allan
authors.initials: A
authors.lastname: Hildesheim
authors.forename: Wim
authors.initials: W
authors.lastname: Quint
mesh_terms: D000293:Adolescent; D000328:Adult; D052685:Alphapapillomavirus / Q000145:classification / Q000302:isolation & purification; D000704:Analysis of Variance; D003364:Costa Rica / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D030361:Papillomavirus Infections / Q000453:epidemiology* / Q000821:virology*; D015995:Prevalence; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D012725:Sexual Behavior