16th International AIDS Conference Toronto, Canada - August 13 - 18, 2006

FALSE POSITIVE ORAL FLUID RAPID HIV TESTS IN SAN FRANCISCO PROMPT NEW TESTING PROTOCOL

Int Conf AIDS. 2006 Aug 13-18;16 Abstract No. TuAc0105

T. Dowling, S. Facente
San Francisco Department of Public Health, AIDS Office, HIV Prevention Section, San Francisco, United States

BACKGROUND: In February 2005, most publicly-funded agencies in San Francisco offering HIV testing began using the OraQuick Advance Rapid HIV-1/2 Antibody Test with oral mucosal transudate. The manufacturer´s stated specificity for this test and specimen type is 99.8% (95% C.I. 99.6% – 99.9%).

METHODS: Since July 2003, the San Francisco Department of Public Health, HIV Prevention Section, has been conducting active surveillance of rapid and confirmatory HIV test results at publicly-funded test sites. Particular attention has been paid to the outcome of preliminary positive rapid test results, including whether that patient was confirmed HIV positive or received a discordant test result (a reactive rapid result with non-reactive or indeterminate confirmatory results). Blood specimens from patients with reactive oral fluid rapid tests were tested with HIV EIA and IFA or Western Blot. After noticing an increase in false positive oral rapid tests in May 2005, we began calculating monthly test specificity and positive predictive value (PPV) by site.

RESULTS: From February to April 2005, among 1755 oral rapid tests, 2 discordant results were observed (0.1%). Both were found to be true positive on subsequent testing (resulting in specificity and PPV of 100%). From May 2005 to December 2005, among 6142 oral rapid tests, 54 discordant results were observed (0.9%). None were found to be true positive on subsequent testing. Assuming all 54 were false positive oral rapid tests, this leads to a specificity of 99.1% and a PPV of 71.3%, with an overall confimed positivity rate of 2.2%. Analysis by month and site showed a marked increase in false positive results at certain sites after September 2005. During 2005, the fingerstick whole blood rapid test performed as expected (specificity 99.8%, PPV 94.2%).

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2006-08-13
TuAc0105

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