MULTIPLE UNCONFIRMED-REACTIVE SCREENING-TESTS FOR VIRAL ANTIBODIES AMONG BLOOD-DONORS

Background: In December 1991, the United States Food and Drug Administ ration received reports of blood donations with unconfirmed reactivity on screening tests for antibodies to human immunodeficiency virus, hu man T-lymphotropic virus type I, and hepatitis C virus (HCV). Of 91 do nors with these test results, 57 (63%) reported a recent influenza vac cination. Study Design and Methods:To determine the extent of unconfir med reactivity, the time at which it began, and its association or non association with specific manufacturers' tests, a nationwide survey of blood centers was conducted. A case-donation was defined as a blood d onation that was repeatedly reactive, but not confirmed positive, on a t least two of the three tests from May 1990 through December 1991. Re sults: Among 14 million donations screened by 110 centers, 582 case-do nations were identified. An increase in case-donations was evident in the fall of 1990 (2.8/100,000 donations). In 1991, rates increased fro m 0.9 per 100,000 donations in the first quarter to 1.3, 3.2, and 19.7 in subsequent quarters. A significantly higher rate of case-donations was observed among donations tested with one of the two available ant i-HCV screening tests (8.0 vs. 1.2/100,000 donations; risk ratio = 6.8 ; 95% Cl = 5.4-8.5). Conclusion: Although unconfirmed reactivity on mu ltiple screening tests appeared to be seasonal, its documentation prio r to the availability of influenza vaccine in 1991 and higher rates am ong donations tested with one manufacturer's anti-HCV test indicated t hat test-specific factors were also involved.