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To the Editor: The Commentary by Dr Gostin¹ discussed the newly revised CDC guidelines on HIV screening. One issue that it did not address is the large number of false-positive tests that will result from switching routine HIV testing from a high prevalence to a low prevalence population. Although discussed on the CDC Web site,² this is not in the context of the new recommendations.

The predictive value of any medical test is a function not only of sensitivity and specificity, but also of disease prevalence. As stated on the CDC Web site, even a test with a sensitivity of 99.9% and a specificity of 99.8% ("similar to that of many rapid HIV tests") will result in 50% false-positive results when prevalence is 0.2%, and 67% false-positive results when prevalence is 0.1%. If 1 million people are tested in a population with 0.1% prevalence, nearly 2000 will falsely be told . . . [Full Text of this Article]

Michael S. Zdeb, MS
msz03@albany.edu
Department of Epidemiology & Biostatistics
School of Public Health
State University of New York at Albany
Rensselaer, NY

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