New HIV screening method, nucleic acid amplification testing (NAAT)

Adding a new HIV screening method, called nucleic acid amplification testing (NAAT), to standard HIV testing, researchers were able to uncover six percent more cases of HIV infection in urban STD and drug treatment clinics and HIV testing sites in Atlanta than with standard HIV antibody tests alone.

The research was presented at the 12th Conference on Retroviruses and Opportunistic Infections in Boston on February 25, 2005 by Frances Priddy, MD, assistant professor of medicine at Emory University School of Medicine.

Physician/researchers at Emory, the University of North Carolina at Chapel Hill and the Georgia Department of Human Resources used NAAT to screen clients receiving routing HIV testing and counseling at the urban clinics between October 2002 and January 2004. The research team used both standard antibody testing and NAAT testing to screen specimens from 2,202 people who had not previously tested positive for HIV. Sixty-six of the specimens were found to be HIV antibody positive and 2,135 were HIV antibody negative using standard tests. Using NAAT, however, four of the antibody-negative specimens tested positive for HIV viral genes.

On further examination, three of those four individuals were found to have definite acute HIV infections, although only one showed clinical symptoms. One of the four individuals had unclear results and may have had either acute or chronic HIV. In addition, three of the four individuals had HIV viruses with multidrug resistance. The fourth sample was unable to be tested for resistance.

Although standard tests that measure antibody response to the HIV virus have become increasingly sensitive, cases of HIV are occasionally missed because individuals can have negative antibody tests during the early stages of infection. Also, a few people with long-term HIV infection may have false-negative antibody tests or may be chronic carriers who are clinically asymptomatic. The NAAT test helps avoid these problems because it amplifies the HIV viral RNA and detects viral genes instead of viral antibodies or antigens.

NAAT testing has been used in the U.S. as an investigational screening test for donated blood since 1999 and was approved for use in 2002 by the FDA. According to a study by the National Institutes of Health (New England J. of Medicine, Aug. 19, 2000), the test has helped prevent the transmission of approximately five HIV-1 infections and 56 hepatitis C virus infections each year since it was initiated for screening donor blood.

"Adding NAAT-based screening to standard HIV testing for can identify people with acute HIV infection earlier when they may be most infectious and at risk for spreading the virus. Then they can be referred for prevention and treatment services earlier before they develop clinical symptoms," Dr. Priddy says. "Early detection and intervention for patients with acute HIV infection may be key in stopping the spread of drug-resistant HIV. Our results show that urban STD and drug clinics and HIV testing sites should consider adopting HIV testing that includes NAAT."