New Test Advances TB Diagnoses

A new test has proved highly accurate at diagnosing tuberculosis and detecting resistance to rifampin in less than two hours and with minimal hands-on time, a new study shows.

Traditional culturing can take a week or more. Using a microscope to look for TB bacteria is faster but can miss many cases and says nothing about resistance.

"If you have 50 patients in a clinic and one person looking at a microscope it could take hours and hours," said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.

Among 1,730 patients with suspected drug-sensitive or multidrug-resistant TB, the automated molecular TB and rifampin-resistance test, Xpert MTB/RIF, correctly identified 98% of patients with smear-positive and culture-positive TB, more than 72% of smear-negative and culture-positive disease, and 98% of rifampin-resistant TB. The study found the test was 99.2% accurate in ruling out patients who did not have TB.

Such an assay could "revolutionize TB care," according to Mario Raviglione, head of the World Health Organization's Stop TB Department. The WHO will meet with experts over the next few days to review the data and make plans for next steps, he said.

Further evaluation will see whether the Xpert MTB/RIF test can detect multidrug-resistant TB. TB that is resistant to rifampin is often resistant to another commonly used treatment, said Fauci.

With relatively minimal training, a health care worker using the test could diagnose TB and rifampin resistance within 90 minutes, according to Catharina C. Boehme, of the Switzerland-based Foundation for Innovative New Diagnostics, and colleagues. It takes only 15 minutes of manual labor to take the mucous sample, mix it with chemicals and place it into an inkjet-like cartridge that goes into the $30,000 machine. The test costs about $63 in Europe, where it went to market last year. Cepheid, the test maker, pledges to offer the test to developing countries for less than half that price and to discount the machine to $20,000.

The study, "Rapid Molecular Detection of Tuberculosis and Rifampin Resistance," was published in The New England Journal of Medicine.