Background:  Recent improvements in the sensitivity of enzyme immunoassays (EIA) used for HIV screening, coupled with increasing recognition of the importance of rapid point-of-care testing, have led to proposals to adjust the algorithm for serodiagnosis of HIV so that screening and confirmation can be performed using a dual or triple EIA sequence that does not require Western blotting for confirmation. One EIA that has been proposed as a second or confirmatory test is the BioRad Multispot Rapid EIA. This test would have the added advantage of differentiating between HIV-1 and HIV-2 antibodies. To compare the sensitivity and type-specificity of an algorithm, we combined a third generation EIA followed by a confirmatory Multispot with the conventional algorithm that combines a third generation EIA (BioRad GS HIV-1-2+0 EIA) followed by confirmatory Western blot (BioRad GS HIV-1 Western Blot).

Methods:  The 8760 serum specimens submitted for HIV testing to the New York City Public Health Laboratory between May 22, 2007 and April 30, 2010, tested repeatedly positive on third generation HIV-1/2+0 EIA screening and received parallel confirmatory testing by Western blot and Multispot.

Results:  Of 8760 specimens, 8678 (99.1%) tested Western blot-positive and 82 (0.9%) tested Western blot-negative or indeterminate; 8690 specimens (99.2%) tested Multispot-positive, of which 14 (17.1%) had been classified as negative or indeterminate by Western blot. Among the HIV-1 Western blot-positive specimens, Multispot classified 26 (0.29%) as HIV-2. Among the HIV-1 Western blot-negative and indeterminate, Multispot detected 12 HIV-2. Repeatedly EIA reactive and Western blot/Multispot-negative/indeterminate were 3 pregnant women who had no detectable HIV-1 RNA or HIV-2 DNA, and 1 EIA reactive and Western blot/Multispot-negative had acute HIV infection. No additional submissions were available for 60 specimens with unresolved or conflicting results.

Conclusions:  Multispot detected an additional 14 HIV-1 infections among Western blot-negative or indeterminate specimens, differentiated 26 HIV-1 Western blot-positives as HIV-2, and detected 12 additional HIV-2 infections among Western blot-negative/indeterminate. A dual third generation EIA algorithm incorporating Multispot had equivalent HIV-1 sensitivity to the third generation EIA-Western blot algorithm and had the added advantage of detecting 12 HIV-2 specimens that were not HIV-1 Western blot cross-reactors. Further testing using nucleic acid detection as the gold standard is needed to calculate specificity and validate the substitution of Multispot for Western blot in the diagnostic algorithm.