Background
Cervical screening programs use testing for Human Papillomavirus (HPV) genotypes. Different HPV types differ greatly in prevalence and oncogenicity. We estimated the impact of cervical screening and follow-up for each HPV type.
Methods and findings
For each type of HPV, we calculated the number of women needed to screen (NNS) and number of women needing follow-up (NNF) to detect or prevent one cervical cancer case, using the following individual level input data i) screening and cancer data for all women aged 25-80 years, resident in Sweden during 2004-2011(N=3,568,938); ii) HPV type-specific prevalences and screening histories among women with cervical cancer in Sweden in 2002-2011(N=4,254); iii) HPV 16/18/Other HPV prevalences in the population-based HPV screening program (N=656,607); and iv) exact HPV genotyping in a population-based cohort (n=12,527). Historical screening attendance was associated with a 72% reduction of cervical cancer incidence caused by HPV16 (71.6%, 95%CI [69.1%, 73.9%]) and a 54% reduction of cancer caused by HPV18 (53.8%, 95%CI [40.6%, 63.1%]). One case of HPV16-caused cervical cancer could be prevented for every 5,527 women attending screening (number needed to screen, NNS). Prevention of one case of HPV16-caused cervical cancer required follow-up of 147 HPV16-positive women (Number needed to follow-up, NNF). The NNS and NNF were up to 40-500 times higher for HPV types commonly screened for with lower oncogenic potential (HPV35,39,51,56,59,66,68). For women below 30 years of age, NNS and NNF for HPV16 were 4,747 and 289, respectively, but >220,000 and >16,000 for HPV35,39,51,56,59,66,68. All estimates were either age-standarized or age-stratified. NNS is dependent on the HPV prevalence that can differ between populations and over time. However, it can readily be recalculated in other settings and monitored when HPV-type specific prevalence changes. The main limitations includes using assumptions to integrate data over time and ages, and very few cervical cancer cases associated with certain HPV types in young age group.
Conclusions
In this study, we observed that the impact of cervical cancer screening varies depending on the HPV type screened for. Estimating and monitoring the impact of screening by HPV type can facilitate the design of effective and efficient HPV-based cervical screening programs.
List of datafiles:
1. Age-specific cervical cancer incidence in Sweden 2004-2011, by screening history in past 10 years;
2. Age-specific HPV genotype prevalence (HPV16/HPV18/Other 12 oncogenic types) in Stockholm population 2012-2019;
3. Estimated age-specific HPV genotype prevalence (by 14 oncogenic types) ;
4. Age-group distribution in Swedish population in 2000 for age-standardization
