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Rapid HIV tests will again allow hospitals to quickly determine the need for post-exposure prophylaxis (PEP) after needlesticks. The Abbott Murex Single Use Diagnostic System (SUDS) HIV-1 test, the only rapid HIV test currently licensed for the U.S. market, was re-released in May. It had been withdrawn in October due to manufacturing problems. The Centers for Disease Control and Prevention and the Food and Drug Administration (FDA) are encouraging the entry of other HIV tests into the U.S. market. About 60 rapid HIV tests are available in other countries.
By using more than one rapid HIV test, hospitals could reduce the likelihood of false positives and improve confidence in the test, says Bernard Branson, MD, a medical epidemiologist in CDC’s division of HIV/AIDS prevention. Rapid HIV tests offer results in as little as 10 or 15 minutes, allowing clinicians to respond quickly with appropriate PEP. However, HIV experts remain concerned about false positives and unnecessary use of PEP in low-prevalence populations.
If the specificity of the test is 99.6%, that means "four out a thousand will be false positives," notes Branson. If a low-prevalence area has an HIV rate of .4%, or four out of a thousand in the population, the testing of a thousand people would produce four true positives and four false positives, he explains. "Half of your positives would be false positives." That problem can be resolved by using more than one type of rapid HIV test, he says. "If the first [test] was positive, you would retest with the second one. If they’re both positive, you have a very high degree of confidence that it’s truly positive."
In rare cases, a hospital might need a third rapid HIV test to resolve a discrepancy between the two, he says. "The majority would only need to be tested once," Branson says. "A positive would need to be tested and, if those two disagreed, it would need to be tested a third time."
For the first time, the use of multiple rapid HIV tests is possible, at least for some hospitals. Trinity Biotech in Dublin, Ireland, received an Investigational Device Exemption for its Uni-Gold HIV test and is recruiting 20 hospitals to participate in the limited trial. The Uni-Gold, which is used worldwide but has not yet been approved by the FDA, has a simple protocol and produces results in about 10 minutes, says Ron Cruver, Uni-Gold product development manager for Trinity Biotech USA in Jamestown, NY. The CDC has been conducting comparative studies on six investigational tests, including the Uni-Gold.
Hospitals also are reporting results with the currently available SUDS test. At the University of Virginia (UVA) Health System in Charlottesville, in a low HIV-prevalence area, 884 SUDS tests performed after needlesticks from January 1999 to September 2000 produced only one false positive, says Heidi Flanagan, RN, HIV and bloodborne pathogen coordinator. While the SUDS test was off the market, 132 tests of source patients using the EIA (enzyme-linked immunoassay) test also produced one false positive, says Flanagan, who presented her results at the April meeting of the Society for Healthcare Epidemiology of America.
Even with rapid HIV tests, the CDC recommends follow-up testing with an EIA, Branson says.
(Editor’s note: Information about the Uni-Gold IDE is available on the Trinity web site, www.trinitybiotech.com.)