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Background: Decreasing incidence of anogenital warts may be an early marker of the impact of human papillomavirus vaccine.
Objectives: To develop and evaluate a case definition for anogenital warts within a managed care organization.
Methods: We identified females and males 11-30 years of age who had received at least one of three ICD-9 codes used for genital warts from 2000 through 2005. Our case definition included persons with a diagnosis of 078.11 (“condyloma accuminatum”) only, or persons with a diagnosis of either 078.10 (“viral warts, unspecified”) or 078.19 (“other specified viral warts”) made by an obstetric, gynecologic, or urologic care provider, or if a test for another STI was ordered at the same encounter. We reviewed medical records on wart diagnosis from a random sample of 250 persons who met our case definition.
Results: The positive predictive value of our case definition for anogenital warts was 82%. Our criterion of a non-specific wart code (078.10 or 078.19) with an STI test ordered at the same encounter generated the most false positives (PPV=34%). The positive predictive value of the ICD-9 code specific for anogenital warts (078.11) was 95%.
Conclusions: ICD-9 codes for anogenital warts are generally non-specific and may lead to overestimation of the incidence of anogenital warts in surveillance studies. By incorporating some additional information about provider type and laboratory tests ordered at the same encounter, we improved the performance of our ICD-9 code-based case definition.
Implications for Programs, Policy, and/or Research:A case definition for genital warts with improved positive predictive value could provide better surveillance data to measure HPV vaccine impact.