Warts transmitted in families and schools: a prospective cohort.

BACKGROUND AND OBJECTIVE Cutaneous warts are common in primary schoolchildren; however, knowledge on the routes of transmission of human papillomavirus (HPV) causing warts is scarce. This study examines the association between the degree of HPV exposure and incidence of warts in primary schoolchildren to support evidence-based recommendations on wart prevention. METHODS In this prospective cohort study, the hands and feet of all children in grades 1 to 7 (aged 4-12 years) of 3 Dutch primary schools were inspected for the presence of warts at baseline and after 11 to 18 months of follow-up. Data on the degree of HPV exposure included information obtained from parental questionnaires: preexistent warts, warts in family, prevalence of warts at baseline in the class, and use of public places (eg, swimming pools). RESULTS Of the 1134 eligible children, 97% participated; the response rate from parental questionnaires was 77%, and loss to follow-up was 9%. The incidence for developing warts was 29 per 100 person-years at risk (95% confidence interval [CI] 26-32). Children with a white skin type had an increased risk of developing warts (hazard ratio [HR] 2.3, 95% CI 1.3-3.9). Having family members with warts (HR 2.08, 95% CI 1.52-2.86) and wart prevalence in the class (HR 1.20 per 10% increase, 95% CI 1.03-1.41) were independent environmental risk factors. CONCLUSIONS The degree of HPV exposure in the family and school class contributes to the development of warts in schoolchildren. Preventive recommendations should focus more on limiting HPV transmission in families and school classes, rather than in public places.