New rapid test identifies active TB

Test may improve early detection

A new rapid tuberculosis test promises to help reduce health care worker exposures through early identification of patients.

The test, called Xpert MTB/RIF, can be performed in less than two hours. In a study involving 1,462 patients with suspected TB, the test correctly identified 98% of those with culture-confirmed tuberculosis and 98% of those with drug-resistant tuberculosis. It also correctly ruled-out tuberculosis in 99% of the patients who did not have TB.

The test isn't available yet in the United States — it isn't approved by the Food and Drug Administration — but already TB experts are touting its prospects.

"The goal right now is to recognize the people who have the symptoms of tuberculosis and to make a presumptive diagnosis and put them in isolation. In the United States, I think they're doing a pretty good job [of doing that]," says Gerald Mazurek, MD, captain in the U.S. Public Health Service and medical officer and epidemiologist in CDC's Division of TB Elimination.

However, there's always a risk that the symptoms of TB will be misconstrued for another respiratory illness and that other patients and health care workers could be exposed before the patient is placed in isolation, he says.

The Xpert MTB/RIF amplifies the nucleic acid in a sputum sample and can identify sensitivity to rifampin, an anti-viral. The test can therefore indicate not only whether a patient has TB, but whether he has a drug-resistant strain.

The testing procedure is simple and involves mixing a reagent with the sputum sample in a cartridge, shaking it and incubating it at room temperature for 15 minutes, and inserting the cartridge into the testing instrument. The remaining steps are automated. "It is definitely user-friendly," says Mazurek.

The test can be used to diagnose active TB but cannot detect latent infection, says Mazurek.