Human papillomavirus 16/18 seroprevalence in unvaccinated women over 30 years with normal cytology and with high grade cervical abnormalities in Australia: results from an observational study

Background: Australia commenced human papillomavirus (HPV) vaccination in 2007, with a two-year catch-up to the age of 26; catch-up cohorts are thus now entering their thirties. Plans for monitoring vaccine impact involve pre- and post-vaccination assessment of cervical HPV DNA in the general population and in high grade abnormalities. Although HPV serology is less sensitive than DNA genotyping, it assesses lifetime exposure and may be easier to measure in the general population. However, benchmark pre-vaccination seroprevalence of vaccine-included types in unvaccinated women with high grade abnormalities has not previously been reported. Methods: We assessed seroprevalence for HPV16/18 from a population-based sample of 3,729 women with normal cytology and 971 women with confirmed high grade abnormalities (CIN2/3), aged 30-64 years, unvaccinated, and recruited in New South Wales in 2006-2010. We examined the variation in HPV16/18 seropositivity by age and in relation to a range of reproductive and behavioural characteristics in the subgroup of normal cytology women with no recent history of high grade cervical disease. Results: The HPV 16, 18 and combined seroprevalence was 19%, 7% and 24% among women with normal cytology, and 39%, 13% and 44% among women with CIN2/3, respectively. For both groups, HPV16/18 seroprevalence was highest at age 30-39 years and decreased with age. In multivariable analysis for women with normal cytology, HPV16 and HPV18 seropositivity were each associated with the number of lifetime sexual partners (p-trend <0.001 and 0.052, respectively) and for HPV16 this was also associated with age (p-trend <0.001) and prior diagnosis of Chlamydia (adjusted OR 1.89, 95% CI 1.27-2.80). Conclusions: The findings of this study inform pre-vaccination estimates of HPV seropositivity in women with normal cytology and women with high grade abnormalities. Almost a quarter of unvaccinated women aged over 30 years with normal cytology, and more than 40% of those with CIN2/3, had seroconverted to HPV 16 or 18. These findings provide a potential additional benchmark for assessing the effects of HPV vaccination.