Feasibility of Tuberculosis Test Proven in Low-Resource Settings

A molecular diagnostic test for tuberculosis (TB) has proven to be both effective and rapid in countries in the developing world that are endemic for the disease.

The assay is a real time polymerase chain reaction (rt-PCR) amplification test that simultaneously detects rifampicin resistance and is used in conjunction with an automated platform, which integrates sample processing and greatly simplifies testing.

A multicenter study is being conducted under the auspices of the Foundation for Innovative New Diagnostics (FIND; Geneva, Switzerland).

South African participants at the University of Cape Town (Cape Town, South Africa), and others from Peru, India, Azerbaijan, the Philippines, and Uganda, enrolled 6,648 eligible adults. The study groups were all aged 18 years or older, with at least two weeks of cough who presented consecutively to urban or periurban primary-care health centers from August 11, 2009, until June 26, 2010. The primary impact outcomes assessed were the time between the first presentation to clinic of a patient with symptoms and the start of appropriate treatment for TB and, secondly, the proportion of patients in each site with undiagnosed TB, two months after the first TB test.

The rt-PCR assay is an automated cartridge based diagnostic system, known as the Xpert MTB/RIF, and was developed for the GeneXpert platform (Cepheid, Sunnyvale, CA, USA). The test correctly detected tuberculosis in more than 90% of patients with positive cultures, with a 99% specificity for nontuberculosis samples. Performance was much the same during validation and implementation phases. A onetime MTB/RIF test identified significantly more cases of tuberculosis than did 2-3 smear microscopy examinations per patient, which detected 699 of 1,041 culture-positive patients and 3,700 of 3,718 patients without tuberculosis. The sensitivity of the MTB/RIF assay was not significantly affected by human immunodeficiency virus (HIV) coinfection status, which significantly decreased the sensitivity of smear microscopy.

The authors concluded that overall, their findings suggest that decentralized MTB/RIF test implementation is feasible and could lead to an improvement in tuberculosis care and control. Any improvement will require increased detection of tuberculosis and multidrug-resistant-tuberculosis to coincide with scale-up of first-line, and more importantly, second-line treatment. Whether early and appropriate treatment after MTB/RIF testing can reduce tuberculosis-associated morbidity and mortality, and its effect on transmission, still needs to be established. The study was published on April 30, 2011, the Lancet.

Related Links:
Foundation for Innovative New Diagnostics
University of Cape Town
Cepheid