Level of HIV in Blood Higher Than Thought

One pint of blood from someone with AIDS contains enough virus to cause nearly 2 million AIDS infections, which helps explain why people who accidentally receive AIDS-tainted transfusions almost always catch the virus, a study by Cedars-Sinai Medical Center researchers in Los Angeles concludes.

The research shows that the blood of people with AIDS contains hundreds of times more virus than experts previously had thought.

The researchers said their work provides new clues about how the virus destroys the body’s immune defenses and should erase any lingering doubts about whether HIV, the acquired immune deficiency syndrome virus, actually causes the disease.

Previous estimates of the level of HIV in infected blood were made about five years ago. In the latest work, the researchers set out to double-check the figures using more sophisticated techniques.

“The answers were quite surprising,” said Dr. David D. Ho, who directed the project. “We found that the levels within the blood cells were orders of magnitude higher.”

Until now, scientists believed that people with AIDS had the virus inside one in every 100,000 of their lymphocytes and monocytes--the white blood cells that are HIV’s chief targets.

The new study found that the level of virus is actually about 250 times higher. The researchers found that at least one in 400 cells harbored the virus. And in some people, one in 200 cells was infected.

The study also found that even when infected people are outwardly well, the virus produces new copies of itself that float freely outside of cells in the blood plasma. This finding challenges the widely held belief that the infection frequently lies dormant for years after the initial infection.

The study and a related paper by Dr. Robert W. Coombs and colleagues at the University of Washington were published in Thursday’s New England Journal of Medicine.