Prevalence of antibodies to HTLV-III in quality-assurance sera.

We tested 146 clinical-laboratory quality-assurance sera for antibodies to human T-lymphotropic virus III (HTLV-III). Of 127 human-based samples, 39 (31%) were positive by an immunoenzymometric assay (IEMA). Samples of human origin that gave IEMA reactivity included four of 10 ethylene glycol-based (liquid) samples, two of six in-house pools of fresh sera, and 32 of 111 lyophilized samples. All 19 bovine-based samples were negative. Antibodies to HTLV-III in 16 samples were remeasured by a second IEMA and the Western blot technique. All assays detected antibody reactivity in four of the 16 samples; however, results of the second IEMA and the Western blot agreed best. We report large discrepancies between assay results when laboratory reagents are tested for HTLV-III antibodies, and find that many quality-assurance samples containing human sera have measurable IEMA reactivity for HTLV-III antibody. Reactivity in these assays indicates the presence of antibody, not viral infectivity.