Is the apparent outbreak of hepatitis A in Belgian hemophiliacs due to a loss of previous passive immunity?

Several reports describing outbreaks of hepatitis A in hemophilia A patients transfused with solvent/detergent-treated factor VIII concentrates have raised concern about possible transmission of hepatitis A by these concentrates. We recently witnessed such an outbreak of hepatitis A in 6 hemophilia A patients; review of the clinical data did not disclose any increased risk factor for community-acquired hepatitis A. A case-control study comparing the prevalence of anti-hepatitis A IgG antibodies in hemophiliacs and age-matched controls showed a lower seroprevalence in hemophiliacs. This might be due to passive protection acquired through transfusion of the previously used immunoglobulin-containing cryoprecipitate. The outbreak of hepatitis A could be explained as a catch-up phenomenon linked to the loss of passive protection with the use of purer factor VIII concentrates.