New tests mark big leap in HIV diagnosis.

Hundreds of scientists packed the vast auditorium, and dozens more gathered in scrums around television screens in the hall outside to hear Martin Markowitz of the Aaron Diamond AIDS Research Center report that a combination of three drugs appears to have eradicated HIV infection in nine people.

"When we look for the virus, we can't find it," Markowitz told the 11th International Conference on AIDS in Vancouver. What Markowitz said next, however, was just as remarkable.

His research team had used a test that can detect just 25 copies of HIV in a milliliter of blood. That's significantly more sensitive than the prototype viral load tests, which can't spot concentrations below 500 copies per milliliter (SN: 3/23/96, p. 184).

Yet even those prototype tests predict the course of AIDS with far greater accuracy than the white blood cell counts used to monitor disease progression for the last 15 years. "The risk of progression [to AIDS] is directly related to the level of virus," says John W. Mellors of the University of Pittsburgh Medical Center.

"These studies have made it increasingly clear that the CD4 [white blood cell] count is at best a gross measure of where a patient stands in the course of HIV disease," says Scott M. Hammer of Harvard Medical School in Boston.

As the Markowitz experiment demonstrates, the tests also make it possible for physicians to gauge the effects of the new multidrug AIDS treatments with exquisite accuracy (SN: 7/13/96, p. 21) and to adjust dosages or select new drugs as soon as a course of treatment loses effectiveness.

The new tests, when coupled with CD4 counts, are expected to enable physicians to predict whether someone who is infected with HIV will live for a prolonged period or die soon.

One study of 1,604 men found that those with fewer than 500 virus particles and more than 700 CD4 cells per milliliter of blood had a 1.7 percent chance of showing AIDS symptoms within 6 years. Those with thousands of viral particles and low CD4 counts faced an 86 percent chance of developing AIDS during that period, said Mellors. Markowitz used an experimental test by Chiron Corp. of Emeryville, Calif., which has a version awaiting Food and Drug Administration approval. Another viral load test, made by Roche Diagnostic Systems of Branchburg, N.J., was approved by FDA last month. The new tests are expected to cost upwards of $150 each when they reach the market. Patients may need to be tested as many as four times per year.