Case Definition

Increasing diagnostic stringency systematically lowered prevalence estimates. The study used antibiotic treatment criteria because intramuscular benzathine penicillin G was available in Japan only from 2021. Syphilis cases were identified by ICD-10 codes A50-A53 and counted only when relevant treatment started in the same calendar month. Transparent case definitions and sensitivity analyses are described as essential for estimating mental health comorbidity with routine insurance data. Reinfection was defined as a new syphilis treatment episode at least 365 days after a previous episode, with exclusions for repeat treatment of late-stage, neurosyphilis, or congenital syphilis. Included stays required vestibular disease, vertigo, or dizziness as the primary discharge diagnosis. Diagnostic certainty was limited because laboratory serology was unavailable in the claims database. A validation step required at least one vestibular-related diagnostic or therapeutic element in the stay. Validation was framed as an internal plausibility and consistency check because no external clinical reference standard was available. The primary diagnosis was the discharge diagnosis justifying admissio…