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New HIV Testing Strategy Improves Detection of Early, Acute Infections, Studies Find

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August 29, 2013

A new testing strategy for screening and diagnosing HIV infections is more effective than traditional ones, according to two studies described in a report published recently by the Centers for Disease Control and Prevention (CDC). By following the steps of the new strategy, also called an algorithm, health care practitioners were able to identify people with acute infections who otherwise would have been missed.

Though local and state public health laboratories recommend use of the new algorithm, it has not been fully implemented in the U.S. The CDC is currently reviewing its recommendations for HIV testing and will consider the results of these studies as it updates its guidance to health care practitioners.

Detecting HIV during the acute, or early, phase of infection is very important because levels of the virus in the body are at their highest during this phase, which increases the potential for transmission. A person diagnosed during this phase has an opportunity to begin treatment and to prevent transmission to others.

The traditional approach to testing, first recommended in 1989, involves performing antibody tests, typically an initial screening test (immunoassay), followed by a second antibody method, usually Western blot (WB) or indirect immunofluorescence assay (IFA), if the initial test is positive. These tests are positive, however, only after HIV antibodies develop, which is usually 2 to 8 weeks after exposure and after the acute, and highly transmissible, phase of the disease.

The new algorithm takes advantage of more advanced testing technology. It recommends screening with combination tests that detect antibodies as well as a portion of the virus particle itself, called p24 antigen. These tests can pick up more acute HIV infections because the p24 antigen can be detected before the development of HIV antibodies. If the combination test is positive, supplemental testing that differentiates between HIV-1 and HIV-2 antibodies is performed. If both the screen and the supplemental test are positive, then the person tested is diagnosed as having HIV. If the supplemental test does not agree with the initial test (is negative), then the new algorithm calls for an HIV RNA test that detects the genetic material of the virus.

The studies described in the June 21 issue of Morbidity and Mortality Weekly Report found that the new testing algorithm used at four investigation centers in four different cities identified a significant number of infections that might have been missed using the traditional testing process. The first study found that by using the new algorithm, 37 previously undiagnosed HIV infections were identified among patients in a Phoenix emergency room who had their blood drawn for other reasons during the study period. This included 12 (or 32.4%) who were in the acute phase of the infection that would not have been found using antibody-only testing methods.

In the second study, conducted in North Carolina, San Francisco and New York City, the screening program found 99 cases with a positive first test and a negative or indeterminate HIV-1/HIV-2 supplemental antibody test; 55 (or 55.6%) were shown to be acute HIV infections (positive for HIV RNA). Large proportions of these acute infections (80%) were negative or indeterminate by traditional supplemental testing methods (WB and IFA) and may have gone undiagnosed, according to the CDC analysis.

In addition to better detection of acute infections, the newer tests may take less time to perform. People who find out about conclusive positive results the same day they are tested may be more likely to receive counseling and treatment. In related news, the Food and Drug Administration announced on August 8, 2013, that it had approved the first rapid point-of-care combination HIV antibody and antigen screening test. Since this test is newly approved, it may take some time before it is widely available for use in the U.S., but it may eventually become another useful screening tool, shortening the time for results even further.

With wider implementation of the new HIV testing algorithm and the possible addition of a new rapid test as a screening option, HIV experts aim to limit the spread of disease from people with acute, early infections and refer them for appropriate treatment sooner.

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used. To access online sources, copy and paste the URL into your browser.

Centers for Disease Control and Prevention. Detection of Acute HIV Infection in Two Evaluations of a New HIV Diagnostic Testing Algorithm — United States, 2011–2013. MMWR, June 21, 2013 / 62(24);489-494. Available online at through Accessed July 16, 2013.

(June 21, 2013) Adler C. New HIV Testing Algorithm Detects Virus Earlier. NEJM Journal Watch. Available online at through Accessed July 16, 2013.

(June 21, 2013) Smith M. Better Testing Catches Early HIV Infection. MedPage Today. Available online at through Accessed July 16, 2013.

(©2013) Association of Public Health Laboratories. HIV Diagnostic Testing Algorithm. Available online at through Accessed August 2013.

(August 8, 2013) FDA approves first rapid diagnostic test to detect both HIV-1 antigen and HIV-1/2 antibodies. FDA News Release. Available online at through Accessed August 16 2013.