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Makers of the new, one-step blood test for detecting latent TB infection are about to start marketing their product to potential U.S. users at $10 a test. They’ll market Quantiferon —- which won approval from a panel of the U.S. Food and Drug Administration (FDA) last October — as a straightforward alternative to the tuberculin skin test (TST), says Jim Rothel, PhD, chief scientific officer for Cellestis, Ltd., the Melbourne, Australia-based firm that makes the product.
That plan sounded somewhat at odds with comments from at least one FDA spokeswoman, who told TB Monitor she hoped the Centers for Disease Control and Prevention, not Cellestis, would work out procedural kinks before the product hit U.S. shelves. The CDC, for its part, suggested using the test primarily as an "adjunct" to the TST.
Rothel says none of that troubles him. "Well, the FDA asked the panel [that was considering Quantiferon] whether the test was to be considered as only an adjunct to the TST," he says, "and the panel replied essentially, Why would you want to do that?’ Of course we want to keep working with the CDC. But we definitely see this test not as an adjunct, but as a straightforward alternative to the TST." Marketing would have started already had not the events of Sept. 11 stalled a visa application. Soon, Rothel adds, the company’s American sales representative should be set up in his California office.
In accordance with FDA directives, Cellestis plans to go ahead with trials of Quantiferon in the two groups for whom the regulatory agency didn’t grant approval for use: children and HIV-positive people. Quantiferon’s U.S. price will run about $10 a test, says Rothel — or, put another way, $440 for a kit that tests 44 people. When the cost for labor is factored in, that’s roughly equal to the cost of administering a TST and then returning to read it, he adds.
At least one TB expert says he’s considering switching to Quantiferon. The $10 price tag "starts to look competitive once you factor in the time it takes to send someone out to read the TST," says Jim McAuley, MD, MPH, the medical director of Cermak Health Services at the Cook County jail in Chicago. "Not only that, my pharmacy director just informed me that our price for Tubersol is about to go up from $2 a dose to $6 or $7."
Quantiferon’s logistical advantages are also appealing, McAuley says. As it stands, Cermak places approximately 100,000 skin tests each year, but jail TB nurses manage to read only 25% to 30% of them, he notes. Because it’s a one-step blood test, Quantiferon doesn’t require going back for a return visit. McAuley is an example of exactly the sort of person Rothel plans to target. "We’re looking at anyone who works in public health where skin testing is done on a large scale, including jails, immigration centers, and that sort of situation," he says.
Meanwhile, Rothel says Cellestis is continuing work on an improved version of Quantiferon that might hit the shelves in three years or so. The new version would do a better job of distinguishing subjects who are merely BCG-vaccinated from those who are latently infected with TB, even though CDC trials show Quantiferon already outperforms the TST at that task, Rothel notes. The next-generation test will work by incorporating recombinant proteins present in TB but absent in BCG, he says. "These are basically pieces of the genome which were deleted when they attenuated M. bovis to make BCG," he explains. "ESAT-6 is the main one you’ve probably heard of."
For now, Cermak’s McAuley says his real challenge will be to figure out how to persuade his labor force to accept the new technology. "It’s always painful when you introduce new technology," he says. Not that using Quantiferon is that hard, he adds: "I’m not a lab guy, and even I can do an ELISA," the basis for the assay, he says. "It’s just that change always comes hard." McAuley adds that one thing he’s not worried about is whether the test works. "I read the JAMA article [detailing results of the CDC trials], and I listened closely to the FDA testimony, and I’m convinced it’s a good test," he says.1
1. Mazurek GH, LoBue PA, Daley CL, et al. Comparison of whole-blood interferon assay with tuberculin skin testing for detecting latent Mycobacterium tuberculosis infection. JAMA 2001; 286:1740-1747.