Seroprevalence and Correlates of Human Papillomavirus 16/18 Seropositivity Among Young Women in Costa Rica

Background: Serological indicators of human papillomavirus (HPV) infection are being used to differentiate HPV-naïve from previously infected women in vaccine and epidemiologic/clinical studies. We investigated HPV16 and 18 seroepidemiology among young, unvaccinated women aged between 18 and 25. Materials and Methods: We conducted a cross-sectional evaluation of the enrollment visit in the ongoing community-based HPV16/18 Costa Rica Vaccine Trial. Prevaccination serum immunoglobulin G (IgG) antibodies were measured against HPV16 and HPV18 by enzyme-linked immunosorbent assay; cervical samples were tested for HPV DNA using Hybrid Capture 2 and SPF10/LiPA25. Seroprevalence and its correlates were evaluated using unconditional logistic regression. Results: Among 5871 nonvirginal women, HPV16 and 18 seroprevalences were 30.8% and 28.1%, HPV16 and HPV18 DNA prevalences were 8.3% and 3.2%, respectively. About 37% of HPV16 DNA-positives and 42% of HPV18 DNA-positives were seronegative. Seroprevalence increased with time since sexual debut, whereas DNA prevalence did not. The correlates of HPV16 and/or 18 seropositivity were related to sexual behaviors, particularly higher number of lifetime sexual partners. There was no evidence of assay cross-reactivity as HPV16 seroprevalence was similar (approximately 34%) among women singly infected with genetically and nongenetically related species (&agr;9 and non-&agr;9); likewise, seropositivity to HPV18 was similar (approximately 30%) among women singly infected with &agr;7 and non-&agr;7 species. Conclusions: The increasing seroprevalence observed with time since first sex suggests that HPV serology is a cumulative marker of HPV exposure. However, many DNA infected women were seronegative; thus, serology is an imperfect measure of past exposure to cervical HPV, at best. Additionally, we found no evidence of assay cross-reactivity.