LACK OF SCREENING-TEST SENSITIVITY DURING HIV-1 NON-SUBTYPE-B SEROCONVERSIONS

Objective: To evaluate the serological consequences of HIV-1 group M d iversity we studied the ability of screening tests to detect anti-HIV antibodies in early seroconverters infected by different HIV subtypes. Setting: Virology Department, Bichat-Claude Bernard Hospital, Paris, France. Design and methods: Symptomatic patients with serial samples a nd with infective strains characterized by heteroduplex mobility assay . In each case, two sera were selected. The first (pre-seroconversion sample) was the last p24 antigen-positive/Western blot-non-reactive sa mple. The second (seroconversion sample) was the first Western blot-re active sample. One second-generation enzyme immunoassay (EIA; Abbott) based on anti-human immunoglobulin (Ig) G-conjugate and three third ge neration EIA (Abbott; Enzygnost; Genscreen) based on the double antige n sandwich principle, detecting IgM and IgG, were used. Results: Ten p atients had subtype B strains and nine had non-B strains (seven were A , one E and one G). The Abbott third-generation test was more sensitiv e than the second generation test for pre-seroconversion subtype B sam ples (nine versus four out of 10; P < 0.05), but not for non-B subtype s; only two of the nine non-B sera tested were positive by both EIA. P ositivity rates and optical densities differed (P < 0.05) between B an d non-B subtypes in all third-generation EIA. There was no significant difference between the subtype B and non-B groups with regard to the interval between the pre-seroconversion sample and the seroconversion sample (subtype B, 6.7 +/- 2.6 days; non-B, 5.2 +/- 1.7 days). No sign ificant difference in positivity rates and optical densities were foun d between B and non-B subtypes in these seroconversion samples. Conclu sion: The shorter time since HIV infection required for sera to become reactive in third-generation EIA screening tests is due to better sen sitivity for subtype B strains only. These results stress the importan ce of strict donor selection, the need to test screening kits against large panels of all subtypes, and the place of p24 antigen testing in closing the window of seroconversion.