Incidence of Genital Warts in Adolescents and Young Adults in an Integrated Health Care Delivery System in the United States Before Human Papillomavirus Vaccine Recommendations

Background: Information on genital wart incidence in adolescents and young adults before human papillomavirus (HPV) vaccination is important for understanding the impact of the vaccine on the epidemiology of this early outcome of HPV infection. Methods: The study population included 11- to 29-year-old enrollees of Northern California Kaiser Permanente between July 1, 2000, and July 1, 2005, before the availability of the HPV vaccine. We identified genital warts with an algorithm combining genital wart-specific International Classification of Diseases, Ninth Revision, Clinical Modification codes (078.10, 078.11, and 078.19) with physician-recorded anatomic locations. We calculated sex-and age-specific incidence rates of genital warts and described the specific anatomic location of presentation, as well as recurrences of genital warts. Results: We identified 1,682 cases of genital warts among 181,264 individuals. The incidence rate was highest among women (6.3/1000 person-years) and men (2.9/1000 person-years) aged 20 to 24 years old. Among women (n = 96,792), 63.4% of the 1240 incident genital wart cases occurred on the vulva and 21.1% on the cervix. Among men (n = 84,472), 91.6% of the 442 incident genital wart cases did not have a specific anatomic location recorded. Most people with an incident genital wart diagnosis (87.2%) did not have a recurrence during the observation period. Conclusions: Our study found that the incidence of genital warts was highest among persons aged 20 to 24 years using a unique method to identify the location of the wart. Information on incidence of genital warts before vaccine use provides baseline data that can be used to measure HPV vaccine impact.