A single window-period donation detected by human immunodeficiency virus p24 antigen after 5 years of routine screening in a group of Brazilian blood banks.

BACKGROUND AND OBJECTIVES: The purpose of this article was to describe the experience of screening for human immunodeficiency virus (HIV) p24 antigen (p24Ag) in blood donors, in four Brazilian Blood Banks, and to report the detection of the first window-period donation. MATERIALS AND METHODS: During 61 months (May 96 to June 01), 103 470 consecutive donations were screened for HIV p24Ag using commercially available enzyme-linked immunosorbent assay (ELISA) kits. Testing was carried out in accordance with the instructions supplied with the kits. RESULTS: Fifty-eight repeatedly reactive samples were identified [0.056% of the total; 95% confidence interval (95% CI): 0.042-0.070]. Ten of the 58 were confirmed as p24Ag positive after neutralization (0.010%; 95% CI: 0.004-0.016), nine of the 10 (0.009%; 95% CI: 0.003-0.014) were also HIV antibody positive and only one (0.001%; 95% CI: 0-0.003) was HIV antibody negative. CONCLUSIONS: In this setting the rate of sole p24Ag-positive donations was one in 103 740. This figure corresponds closely with the previously estimated yield of one in 87 796 donations. The yield of HIV p24Ag+ : Ab- has been previously estimated in our centres to be 1 : 87 796 donations, a value similar to that observed in actual practice.

Serologic testing for Trypanosoma cruzi: comparison of radioimmunoprecipitation assay with commercially available indirect immunofluorescence assay, indirect hemagglutination assay, and enzyme-linked immunosorbent assay kits.

The radioimmunoprecipitation assay (RIPA) has been used as a confirmatory test in several ongoing and published studies of Trypanosoma cruzi in blood donors in the United States. Despite its use as a confirmatory test, few studies are available comparing RIPA to commercially available serologic test methods. Thus, we compared RIPA with two indirect hemagglutination assays (Biolab Diagnostica SA, São Paulo, Brazil; Hemagen Diagnostics, Inc., Waltham, Mass.) and four different enzyme-linked immunosorbent assays (Abbott Laboratories, Abbott Park, Ill.; Embrabio, São Paulo, Brazil; Organon Teknika, São Paulo, Brazil; and Gull Laboratories, Salt Lake City, Utah) using a panel of 220 serum specimens from Brazilian blood donors with a range of T. cruzi antibody titers as determined by indirect immunofluorescence assay (IFA). A titer of 1:20 was used as the baseline for seropositivity. All IFA-negative serum specimens (n = 19) were nonreactive on all tests. At a titer of 1:20 (n = 9), reactivity rates varied considerably among the tests, with only the RIPA and the Organon and Gull assays identifying reactive specimens. For specimens at a 1:40 titer (n = 35), most assays identified at least 32 of 35 (91%) specimens as reactive, but the Biolab assay only identified 24 (69%). At higher titers (1:80, n = 56; 1:160, n = 101) the assays were comparable, with the exception of the Biolab assay, demonstrating rates of agreement with IFA of >/=98%. Overall, when compared with several other test formats, RIPA demonstrated equivalent or superior rates of agreement with IFA-positive specimens across all titers examined. In particular, at titers of >1:40, the RIPA compared favorably with other test methods currently in use, supporting its application as a confirmatory test, particularly in a research setting.