The discovery that a virus caused AIDS shifted some research efforts toward a focus on the biological aspects of transmission of the disease and its interactions within the human body. The public's reaction to the discovery of HTLV-III (later renamed HIV) included an increased fear of casual transmission and of infection through the act of donating blood (Fee and Fox 1988; Brandt 1987). As a result of the isolation of HTLV-III, blood and plasma collection organizations, anticipating the quick development of a direct test for the virus, did not implement any additional donor screening procedures until such a test was developed. Meanwhile, during 1982–1984, U.S. manufacturers were completing the development of a process for inactivating the hepatitis B viruses by heating AHF concentrate (see Chapter 4). In October 1984, the CDC announced that laboratory experiments showed that the heat treatment process also inactivated HIV.

During 1984, however, researchers remained focused on developing a screening test for HIV. Once the virus was identified, several companies began developing tests to screen blood by detecting antibodies that would indicate exposure to the virus. In April 1984, NIH developed and patented a prototype screening test for antibodies to HIV, and by May it had solicited applications from companies interested in commercial use of the tests. Five companies were selected in June. The first tests used an enzyme-linked immunosorbent assay (ELISA), and the FDA received an application for licensure from a company in December 1984. By March 1985, the FDA had granted two licenses for commercial use of the tests; it also notified all blood facilities that the test was available, and it scheduled a workshop on its use [50 Federal Register 28477]. Subsequently, all blood banks and plasma collection centers implemented the ELISA.

The first ELISA tests detected 96–98 percent of HIV-infected blood samples. However, despite a high degree of specificity, false seropositive results occurred. For this reason, a second, more costly, less sensitive, but more specific screening test called the Western Blot was used to confirm or refute the positive results of the ELISA test. Neither test could detect HIV antibodies during the six-to-eight-week window period (i.e., the time between HIV infection and the evidence of antibodies in a donor's blood). Since the implementation of the initial ELISA test, several more sensitive tests have replaced it because they reduce the length of the window period. Through the widespread use of this test, the current risk of HIV transmission through screened blood is estimated to be less than 1 in 420,000 units (Lackritz, et al. 1995; Busch, et al. 1995).

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