Doctors have recently been alerted to the possibility that intravenous immune globulin given to build up natural antibodies and to treat hepatitis C can actually trigger the disease.
More than 100 cases were recorded in the US last year, and a new group of victims has been reported in Norway.
Researchers are still looking into the reasons why so many incidents should suddenly occur, particularly as tens of millions of grams have been administered without any apparent problems.
Researchers from Norway believe the outbreak among 20 patients was caused by contaminated stock.