Evaluation of an expanded two-ELISA approach for confirmation of reactive serum samples in an HIV-screening programme 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 virus (HIV) infection. The sera of 56 (0.179%) women tested were confirmed as positive for HIV. A total of 67 sera reacted positive or borderline by the screening enzyme-linked immunosorbent assay (ELISA) and indeterminate or negative by HIV-1 Western blot; 42 of these specimens were available for evaluation of the strategy for diagnosis of HIV infection. 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 HIV-1 gp41 and HIV-2 gp36 envelope proteins, was compared with the Western blot analysis. Indeterminate results were resolved with a nucleic acid sequence-based amplification assay (NASBA) for HIV-1 RNA and a strip immunoassay (SIA) for the simultaneous detection of antibodies to HIV-1 or HIV-2 and HIV-1 p24 antigen. Eleven samples were weakly or borderline 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 test and negative results by Western blot. Again, these sera were characterised as HIV-negative by the expanded two-ELISA procedure, and this characterisation was confirmed by both NASBA and the SIA. Five HIV-2-positive serum samples were recognised by the expanded two-ELISA approach and the SIA; these sera were negative by NASBA. Finally, another five serum samples were weakly or borderline positive by both ELISAs and positive by the membrane immunoassay; of these five, two sera generated positive patterns and the other three indeterminate patterns on Western blots, and four were positive by the NASBA assay. Follow-up serum specimens from these five women were negative and the reactivity of the initial specimens was thus likely to have been the result of cross-contamination. Our results demonstrate the effectiveness of a simple confirmation approach of two HIV ELISAs expanded with a membrane spot assay to discriminate between infection with HIV-1 or HIV-2. The data also indicate the importance of retesting individuals with indeterminate or positive confirmational results to exclude the possibility of contamination as the cause of reactivity of the original specimen. (C) 1998 Wiley-Liss, Inc.