Seroprevalence and genital DNA prevalence of HPV types 6, 11, 16 and 18 in a cohort of young Norwegian women: study design and cohort characteristics

Background. Long-term efficacy evaluations of a quadrivalent HPV type 6/11/16/18 vaccine are ongoing in the Nordic region. As there are limited epidemiological data on HPV infection in Norway, we determined prevalence and identified sociobehavioural correlates of HPV 6/11/16/18 infection in young Norwegian women. Methods. Norwegian (n=898) women, aged 16-24 years, were enrolled in a 4-year prospective study. At enrolment and at 6-month intervals thereafter, an interview on behavioural data and a gynaecological examination were undertaken. Genital samples were tested for the L1, E6 and E7 genes of HPV-6/11/16/18, and serum anti-HPV-6/11/16/18 levels were measured using a competitive Luminex immunoassay (cLIA). Results. DNA and seroprevalence of HPV 6, 11, 16 or 18 ranged from 0.9 to 16.3% and 2.6 to 16.2%, respectively; and most infected women (∼75%) were infected with only 1 type. Of the HPV DNA positive cases, 54.3, 50.0, 47.3 and 38.5% had detectable HPV 6, 11, 16 or 18 antibodies, respectively. More than 50% of the high-grade cervical intraepithelial neoplasia (CIN) cases were HPV-16 or HPV-18 DNA positive. Lifetime number of partners was the strongest and only predictor of sero- and DNA-positivity across the 4 HPV types. Conclusion. Given the high prevalence of HPV infection among young women with mostly single-type infection, and the fact that type-specific HPV screening is not recommended prior to the administration of the quadrivalent HPV vaccine, our data suggest the importance of widespread, rather than targeted, immunisation.