During the years 1970-1972, the HBsAg test was required and implemented in all blood and plasma collection organizations. In July 1975, the use of a third-generation test for HBsAg with a greater degree of sensitivity, utilizing radioimmunoassay or reversed passive hemagglutination, was required by the FDA. In 1977, the World Health Organization Committee on Viral Hepatitis adopted the terms hepatitis A for the hepatitis virus transmitted orally, and hepatitis B (HBV) for the virus transmitted sexually and through transfusion of blood or blood products.

As a result of the implementation of HBsAg testing during the period from 1972–1975, AHF concentrate testing positive for HBsAg decreased from 25 percent to 3 percent of Factor VIII lots tested by the FDA, and from 67 percent to 2 percent of Factor IX lots tested by the FDA. After 1975, according to Dr. Robert Gerety, chief of the Hepatitis Branch, Division of Blood and Blood Products in the Bureau of Biologics at the FDA at the time, no lots of either Factor VIII or Factor IX submitted to the bureau contained detectable HBsAg; but despite this, the problem of HBV infection following administration of the AHF concentrate would remain serious (Gerety and Barker 1976).

By 1975, even though third-generation testing was in practice, some donations of blood or plasma had levels of HBsAg that were below the level of assay detection and HBV-infected donations continued to enter the pools used in the plasma lots. Even though these lots contained undetectable levels of HBsAg, owing to the extraordinary infectivity of HBV, they were still able to transmit the infection to susceptible recipients of the affected blood products. However, in 1976, although 80 percent of individuals with hemophilia were identified as positive for the antibody to hepatitis B (evidence of previous infection with the virus), the majority did not develop clinically apparent hepatitis. The percentage of individuals with hemophilia with chronic HBV infection ranged from 2.5 to 7.8 percent and the percentage of those who had clinically recognizable hepatitis ranged from 6 to 26 percent. Gradually, it was believed by the medical community treating individuals with hemophilia that many adults with hemophilia had developed an immunity to HBV as a result of prior exposure to the virus (Aledort, Dietrich, Levine interviews). Administration of the AHF concentrate to children and adolescents with hemophilia, however, often resulted in clinical and chronic HBV infections (Gerety and Barker 1976). Once screening for HBV markers resulted in the exclusion of HBV carriers in the donor pool, NANB virus was responsible for 80–90 percent of the hepatitis cases. Prospective studies performed in the late 1970s and early 1980s indicated that the incidence of post-transfusion hepatitis (HBV and hepatitis C [HCV]) was 7–21 percent in recipients of blood from volunteer donors (Barker and Dodd 1989). The infectious nature of NANB hepatitis was first established in 1978 by experimental transmission to

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