Monitoring

A large and growing market--often overlooked--involves assays used by patients to track the disease and help make treatment decisions. According to Frost & Sullivan, this market reaped $92.3 million in revenues last year, two-thirds of which came from tests that measure levels of white blood cells with a receptor known as CD4, the docking point used by HIV's surface protein to infect cells. CD4 cell counts have become a bellwether for health status, because HIV selectively destroys them, giving an indication of how much damage has been done to the immune system. Frost & Sullivan analysts project that in 2000, CD4 tests alone will gross $128.4 million.

The rest of the monitoring market assesses the other side of the AIDS equation--how the virus is doing. A crude gauge of the pathogen's strength is a popular test that measures the viral protein p24. In clinical studies the p24 test has now been supplanted by more sensitive assays that measure levels of HIV's nucleic acid in plasma, recently shown to be powerful predictors of a person's disease course (Science, 9 February, p.755). On 3 June, the first of these new "viral load" tests won FDA approval. Made by Roche Molecular Systems, this test uses the polymerase chain reaction to amplify HIV RNA. Already, competitors are preparing to enter the market. One of the strongest is likely to be one made by Chiron known as "branched DNA."

Mike Richey, Chiron's vice president of diagnostics sales, estimates that the potential U.S. and European market for all viral-load tests is $80 million to $120 million. His method of calculating the figure is revealing. Richey postulates that half of the HIV-infected people in the United States do not even know they have the virus. Of the other half, past sales of anti-HIV drugs reveal that, at most, 200,000 are being treated. Maybe another 50,000 are being seen by physicians. The rest know their status but are outside the health care system.

Richey assumes that the 250,000 people visiting clinics or physicians will each receive four viral-load tests a year--which would mirror the frequency of current CD4 tests. If each new test sold for $50 to $75, the current price of the Chiron kit, that wo uld translate to revenues of $50 million to $75 million in the United States. The European market is thought to be about 60% as large.