EVALUATION OF AN EXPANDED 2-ELISA APPROACH FOR CONFIRMATION OF REACTIVE SERUM SAMPLES IN AN HIV-SCREENING PROGRAM FOR PREGNANT-WOMEN

Serum specimens were collected from 31,232 pregnant women in Amsterdam between 1988 and 1995 in a screening programme for human deficiency v irus (HIV) infection. The sera of 56 (0.179%) women tested were confir med as positive for HIV. A total of 67 sera reacted positive or border line by the screening enzyme-linked immunosorbent assay (ELISA) and in determinate or negative by HIV-1 Western blot; 42 of these specimens w ere available for evaluation of the strategy for diagnosis of HIV infe ction. A two-ELISA approach with the second ELISA based on a principle different from that of the screening ELISA, expanded with the use of a membrane immunoassay based on two synthetic peptides specific for HI V-1 gp41 and HIV-2 gp36 envelope proteins, was compared with the Weste rn blot analysis. Indeterminate results were resolved with a nucleic a cid sequence-based amplification assay (NASBA) for HIV-1 RNA and a str ip immunoassay (SIA) for the simultaneous detection of antibodies to H IV-1 or HIV-2 and HIV-1 p24 antigen. Eleven samples were weakly or bor derline positive by the screening test and gave indeterminate results by Western blot. The expanded two-ELISA approach designated these sera as HIV-negative, and confirmed negative by NASBA and the SIA. Twenty- one samples showed borderline or positive results on the screening tes t and negative results by Western blot. Again, these sera were charact erised as HIV-negative by the expanded two-ELISA procedure, and this c haracterisation was confirmed by both NASBA and the SIA. Five HIV-2-po sitive serum samples were recognised by the expanded two-ELISA approac h and the SIA; these sera were negative by NASBA. Finally, another fiv e serum samples were weakly or borderline positive by both ELISAs and positive by the membrane immunoassay; of these five, two sera generate d positive patterns and the other three indeterminate patterns on West ern blots, and four were positive by the NASBA assay. Follow-up serum specimens from these five women were negative and the reactivity of th e initial specimens was thus likely to have been the result of cross-c ontamination. Our results demonstrate the effectiveness of a simple co nfirmation approach of two HIV ELISAs expanded with a membrane spot as say to discriminate between infection with HIV-1 or HIV-2. The data al so indicate the importance of retesting individuals with indeterminate or positive confirmational results to exclude the possibility of cont amination as the cause of reactivity of the original specimen. (C) 199 8 Wiley-Liss, Inc.