post-transfusion HIV infections from donations in the "window" period (the time period between infection with the virus, but prior to a detectable antibody response in blood or plasma) continued to occur. In order to evaluate the effect of adding the p24 antigen test (a viral antigen that can be present in the window period), 500,000 donors in 10 different areas in the United States were tested for p24 (Alter, et al. 1990). As no cases of p24 positive blood donors were found, the test was not implemented on a wide-scale basis.
HIV-2 is a retrovirus that is distantly related to HIV-1 (HIV) that also causes AIDS in humans. Although it is prevalent in areas of West Africa and other parts of the world, it is only very rarely found in the United States. Despite its rarity in the United States, the FDA required that all blood donations be screened for HIV-2 in April 1992. A new variant, known as HIV subtype 0, has also been described and may also be included in the routine screening in the future.
Post-transfusion non-A, non-B hepatitis cases continued to be reported. Without any evidence that the causative agent would soon be elucidated, surrogate tests were suggested. Based on previous studies and new evidence, the surrogate testing for non-A, non-B hepatitis was instituted during 1986–1987 by using both the ALT and Anti-HBc tests. In 1989, the genomic structure of a putative NANB virus (Hepatitis C virus [HCV]) was discovered. As a result, a test for antibodies to the HCV virus was licensed and implemented as a screening test for HCV in 1990.
In an NIH consensus conference held in January 1995 (there was no other consensus conference held earlier by the NIH), it was recommended that the ALT surrogate test be discontinued. However, anti-HBc was retained, not as a non-A, non-B surrogate marker, but as a second hepatitis B screening test for cases with low HBsAg titer.
In 1988 six positive HTLV-I cases were reported among 40,000 donors (Williams, et al. 1988). In November 1988, a screening test for HTLV-I (virus that causes leukemia and myelopathy) was instituted for all blood units. HTLV-I has been found in the United States, but HTLV-II has been seen more frequently. Not all blood donors with HTLV-II infection are effectively identified using the HTLV-I antibody tests; instances of transmission of HTLV-II by blood screened negative for HTLV-I have been reported.