The seroprevalence of anti-JCV antibodies in Spanish MS patients' cohort was between 55.3 and 60.5%.
Seroprevalence JCV only increased with age and when 2nd generation ELISA was employed.
The seroconversion rate was 7% per year.
Changes in serostatus were observed in 8% of our patients.
Fluctuations on serological status were associated with antibody index near to assay's cut-off.