RESUMEN
OBJECTIVE: To estimate the seroprevalence of anti-JCV antibodies, seroconverting rates and evolution of antibody levels in a multiple sclerosis (MS) Spanish cohort. METHODS: Multicenter, retrospective cross-sectional and longitudinal study. The JCV seroprevalence was analyzed in 711 MS patients by using 1st (STRATIFY-1) and 2nd generation (STRATIFY-2) two-step ELISA over 2.65 (±0.97) years. Seroconversion rate was obtained over 2 samples from 314 patients, and index stability from 301 patients with 3 or more samples available. The effect of each ELISA generation, demographics, clinical characteristics and therapy on seroprevalence was assessed by logistic regression. RESULTS: The overall anti-JCV seroprevalence was 55.3% (51.6-58.9), similar across regions (p=0.073). It increased with age (p<0.000) and when STRATIFY-2 was used (60.5%, p=0.001). Neither sex nor immunosuppressive therapy had any influence. Yearly seroconversion rate was 7% (considering only STRATIFY-2). Serological changes were observed in 24/301 patients, 5.7% initially seropositive reverted to seronegative and 7% initially seronegative changed to seropositive and again to seronegative, all these cases had initial index values around the assay's cut-off. CONCLUSIONS: JCV seroprevalence in Spanish MS patients was similar to that reported in other European populations. Changes in serostatus are not infrequent and should be considered in clinical decisions.