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Background: The quadrivalent HPV vaccine, available in the United States since 2006, prevents disease due to HPV types 6 and 11, which cause 90 percent of genital warts (GW). Because of the rapid development of GW after infection, monitoring trends in GW may provide early evidence of population-level vaccine effectiveness.
Objectives: Examine trends in GW diagnosis using family planning administrative claims data.
Methods: Trends in GW diagnoses were assessed using clinical encounter claims data from the California Family Planning Access Care and Treatment program. GW cases were defined as unduplicated clients with either an International Classification of Diseases (ICD-9) diagnostic code for viral warts (078.10) or condyloma (078.11), or a National Drug Code (NDC) for pharmacy-dispensed imiquimod or podofilox. Denominators included unduplicated clients served. The proportions of clients with GW were stratified by age (<21 years, 21-25, 26-30, 31+), gender, and year. Statistical significance was assessed using the Cochran-Armitage test for linear trend.
Results: Between 2007 and 2009, an average of over 1,735,000 female and 248,000 male clients were served annually. Overall, 0.7 percent of females and 3.4 percent of males were diagnosed with GW. Between 2007 and 2009, GW diagnoses declined 19.4 percent among females younger than age 21 (p for trend < 0.0001), whereas GW diagnoses were stable or increasing among females in older age groups and males.
Conclusions: This analysis provided preliminary evidence that the HPV vaccine may be preventing GW among young women. Although using existing administrative claims data to assess trends in HPV-related diseases was inexpensive and expeditious, trends are ecological and may be explained by factors other than vaccination.
Implications for Programs, Policy, and Research: Efficient and effective surveillance methods are key to monitoring the health impact of HPV vaccines.