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Genetic Testing Picks Up More HIV Infections

It may detect 4 percent of missed cases, study suggests

WEDNESDAY, May 4, 2005 (HealthDay News) -- New research offers more evidence that expanded HIV tests could pick up infections that would otherwise go undetected in the United States each year.

Scientists report that a new type of genetic testing uncovered 23 cases of HIV among 109,250 people who were screened in North Carolina over the course of a year. Routine HIV tests missed all the cases.

The number may seem small considering that 606 of those tested turned out to be HIV-positive. But the big picture is disturbing, said Dr. Christopher Pilcher, an assistant professor at the University of North Carolina School of Medicine's infectious diseases division, and co-author of the study in the May 5 issue of the New England Journal of Medicine.

"This study suggests that as many as 4 percent of all the HIV infections may be missed, despite [the patients] coming in and requesting testing," Pilcher said.

The good news is the genetic testing approach is inexpensive and effective, Pilcher said, and it lets health officials promptly warn the sexual partners of an infected person.

"Those are 23 people who would [otherwise] have been sent home with the sense that everything's fine, they're not infected," said Dr. Willi McFarland, head of HIV surveillance for the San Francisco Department of Health.

Traditional HIV tests detect antibodies, the soldiers of the immune system that gather to fight germ invaders. But it takes a while for the antibodies to develop, and an HIV test may turn out a negative result when a person is actually HIV-positive.

Although the antibody tests have become more precise, allowing them to catch more recent infections, they can still miss the virus in people who were infected within the past few weeks.

"When someone is infected, the virus initially focuses its attack on the lymph nodes and establishing a beachhead in the patient's lymphatic system," Pilcher said. "After a week or two, it spills into the blood. Antibodies take another week or two to develop."

The virus is also especially strong in the first weeks after infection, before the body's defenses kick in. Some AIDS specialists estimate that most HIV infections occur because somebody has unprotected sex within the first few weeks after being infected.

Enter the nucleic acid amplification test, which detects the presence of the virus in the blood within one to two weeks of infection. There's a catch, however. The test is wrong about 10 percent of the time, and patients with a positive result must still go back to get a traditional antibody test after a few weeks, Pilcher said.

The researchers found genetic testing added $3.63 to the cost of each test. The study didn't report the total cost of a test.

The new research bolsters the findings of a smaller study, released in February, which found that the genetic test uncovered three cases of recent HIV infection among 2,135 people who were screened in the Atlanta area. Traditional HIV tests hadn't uncovered any sign of the virus that causes AIDS in the patients.

Only a few cities are testing the new approach, Pilcher said, but he's happy that health officials are moving toward studying or implementing the new testing strategy.

"It's definitely caught a lot of people's interest," said McFarland, who added the approach is being used in San Francisco.

More information

To learn about new rapid HIV tests, try the U.S. Centers for Disease Control and Prevention.

SOURCES: Christopher Pilcher, M.D., assistant professor, University of North Carolina School of Medicine's infectious diseases division, Chapel Hill; Willi McFarland, M.D., Ph.D., director, HIV surveillance, San Francisco Department of Health; May 5, 2005, New England Journal of Medicine
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