An outbreak of hepatitis A among Irish haemophiliacs

An outbreak of hepatitis A (HAV) occurred in 1992 in Irish haemophilia A patients treated with high purity solvent-detergent (SD) treated factor VIII. Similar outbreaks were reported in Italy, Germany and Belgium. The aim of this study was to investigate the outbreak, and to test the hypothesis that it was caused by exposure to SD-treated factor VIII.

A case-control study was started in early 1993. Haemophilia A cases with acute HAV (n = 29) were compared with haemophilia A controls for exposure to SD-treated factor VIII and other environmental factors. Details of factor VIII usage were obtained from the National Haemophilia Register and environmental data were obtained by a telephone-administered questionnaire. The response rate was approximately 90%.

The incidence of acute HAV infection among haemophilia A patients exceeded the notified national incidence of HAV by a factor of approximately 300. The incidence was higher in younger patients and those with more severe bleeding disorders. Contact with hepatitis, with children, and exposure to factor VIII were associated with increased risk. The association with factor VIII was the strongest risk factor after controlling for other factors (odds ratio = 27.6, 95% confidence interval [CI] 6.5-117.3). A dose-response effect was demonstrated.

Although person-to-person transmission is likely to have caused a few of the cases, the results of our investigation suggest that the major contributing factor was exposure to certain batches of SD-treated factor VIII.