Prevaccination distribution of human papillomavirus types in women attending at cervical cancer screening in Belgium.

INTRODUCTION Before the introduction of vaccination against human papillomaviruses (HPV) as a new strategy of combating cervical cancer, it is required to describe the baseline prevalence of HPV infection as well as the distribution of the different HPV types in the population and among women with cervical lesions. MATERIALS AND METHODS Approximately 10,000 liquid cervical cell samples from women, resident of Flanders (North Belgium) and participating in cervical cancer screening, were assessed cytologically and virologically with a multiplex real-time PCR using primers targeting the E6/E7 genes of 16 HPV types. Correlations of HPV infection with age, geographic area, and occurrence of cytologic lesions were assessed. RESULTS The prevalence of cytologic abnormalities was atypical squamous cells of undetermined significance (ASC-US), 1.6%; atypical glandular cells (AGC), 0.2%; low-grade squamous intraepithelial lesion (LSIL), 2.6%; atypical squamous cells, HSIL cannot be excluded (ASC-H), 0.3%; and high-grade squamous intraepithelial lesion (HSIL), 1.2%. The frequency of high-risk HPV infections was 11% in women without cytologic abnormalities, 77% in ASC-US, 32% in AGC, 85% in LSIL, and 93% in ASC-H and HSIL. The prevalence of high-risk HPV infection was highest in women of ages 20 to 24 years (29%) and decreased progressively with age. The percentage of women with HSIL in the entire study population attributable to infection with a particular type (AR(pop) %) was highest for HPV16 (32%), followed by HPV31 (22%), HPV39 (11%), and HPV52 (11%). HPV18 was responsible for 7% of the HSIL lesions. Elimination of HPV16 and HPV18 is expected to reduce the prevalence of ASCUS with 24%, AGC with 19%, LSIL with 29%, ASC-H with 31% and HSIL with 37%. DISCUSSION Compared to other West European studies, the prevalence of HPV infection was considerably higher in cytologically negative women but similar in women with cervical lesions. These differences could be due to the use of a PCR with high analytic sensitivity. These data are relevant for estimating the expected and theoretical levels of vaccine protection offered as vaccinated girls gradually age into the groups from which our observations stem. Further periodic laboratory-based surveys, including genotyping of cervical cell samples and linkage with vaccine registries, are an important resource to address pending questions of the effect of HPV vaccination. Research is warranted to disentangle the causal role of individual HPV types in case of multiple infections.