Over the past several months, there have been numerous mainstream media reports regarding an unusually high number of false-positive HIV-antibody test results using the oral-based OraQuick rapid assay (the reliability of the blood-based OraQuick assay hasn't been disputed). Dr. Bernard Branson and his colleagues at the U.S. Centers for Disease Control have investigated these reports and reported their findings at the 13th Conference on Retroviruses and Opportunistic Infections in Denver.
Dr. Branson's group looked at three testing sites in New York City that have reported excessive false-positives (cases), along with seven sites in the city that have not reported excessive false-positives (controls). And in San Francisco, his group looked at one site with excessive false-positive and 11 sites without excessive false-positive test results.
Using November 2005 as an example, 1581 individuals were tested throughout the month at one of the three case clinics in New York City. There were 32 false-positive rates in total, yielding a testing specificity of 98%. Among the seven control testing sites, 2164 people were tested in November. There were three false-positive test results, putting the specificity at 99.9%. In San Francisco during the same month, 160 oral-based tests were conducted at the case clinic, six of which turned out to be false-positive (yielding a specificity of 96.3%). In the 11 control clinics, 551 tests were conducted, with five false-positive test results (yielding a specificity of 99.1%).
The FDA minimum threshold for specificity is 98%. Dr. Branson's group concluded that the false-positive results are not likely a limitation of the oral-based test themselves, but rather attributed to site-specific factors, including the possibility of procedural errors. The CDC is still looking into the discrepancies.
Source: Branson B, Wesolowski L, Delaney K. et al. Investigation of reports of excessive false-positive oral fluid rapid HIV tests [Abstract 34LBb]. 13th Conference on Retroviruses and Opportunistic Infections, Denver, 2006.
