Cepheid's Xpert MTB/RIF automated nucleic acid-amplification tuberculosis and rifampin-resistance test may be a "game changer" in effectively treating TB cases in the developing world, according to a study and editorial in the Sept. 1 New England Journal of Medicine.

The test provides results in two hours and can be used by relatively unskilled health care workers in the field.

If an advanced, rapid nucleic-acid amplification test such as Xpert is adopted globally, "it could help avert more than 15 million tuberculosis-related deaths by 2050," write NEJM editorialists Peter Small, M.D., of the Bill and Melinda Gates Foundation, and Madhukar Pai, M.D., of the McGill University Department of Epidemiology, Montreal.

However, adoption of the Cepheid test will hinge heavily on pricing and whether health systems in developing nations are strengthened so that patients do not delay in seeking care after testing, the editorial says.

Governments Must Look At Test Costs Holistically

Cepheid CEO John Bishop told "The Gray Sheet" that the original $64 price of the test has been brought down to $32 for developing countries through negotiations with the Foundation for Innovative New Diagnostics (FIND) and the Bill and Melinda Gates Foundation. Bishop added that the $30,000 cost of the GeneExpert platform that the test runs on will drop to under $10,000 as more countries take advantage of it, and as sales volumes increase.

Governments considering use of the Xpert test and the platform "have to look at their total costs" and should think of testing costs holistically in terms of what other health care spending could be avoided if the test is used, Bishop maintained.

The exec noted that since Cepheid has already obtained European CE-mark approval for the TB test, he expects developing countries to follow suit. Cepheid has already received approval in Brazil and is pursuing market go-ahead in China. In the U.S., PMA approval is not expected until 2012, he said.

The Sept. 1 NEJM study by Catharina Boehme, et al., from FIND, assessed the performance of the Xpert MTB/RIF test on 1,730 patients with suspected drug-sensitive or multidrug-resistant pulmonary tuberculosis at five sites in Peru, Azerbaijan, South Africa and India between July 2008 and March 2009.

The study was designed and supervised by FIND, with additional funding and development support provided by the National Institutes of Health, Cepheid and the Bill and Melinda Gates Foundation.

Test Is 98.2% Sensitive For Smear-Positive TB

Study results showed a single, direct MTB/RIF test had a 98.2% sensitivity rate, correctly identifying 551 of 561 patients with smear-positive TB. The sensitivity rate was 72.5% for smear-negative TB patients, as the test identified 124 of 171 patients with smear-negative TB. The test also showed a specificity rate of 99.2%, and accurately detected resistance to the anti-TB drug rifampin in more than 97% of patients.

Discussing the results, Boehme et al. said that advantages of the test are its quick, two-hour turnaround time, and that it performed better than smear microscopy for the diagnosis of TB patients with smear-negative TB at two South African sites with a 60% to 80% prevalence of HIV infection.

Researchers also pointed out the simplicity of the test, with the DNA extraction, amplification and detection step fully automated within a cartridge.

The only manual step required by health care workers administering the test is to add a bactericidal buffer to sputum samples before transferring the sample to the cartridge. This means that local technicians could be trained in only two to three days to perform the tests.

However, the researchers were uncertain that the test results, which were processed at reference laboratories for the study, could be replicated at the microscopy centers, health posts and other point-of-care facilities where it would be needed in developing countries.

- Sue Darcey ( ¹ s.darcey@elsevier.com )

Field-Ready, Automated Cepheid TB Test Shows Promise In Developing World

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