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Xpert diagnostic tool increases TB detection rate, treatment initiation

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January 13, 2017

New research found that a community-based strategy involving a nucleic-acid amplification test that can detect both Mycobacterium tuberculosis DNA and rifampicin resistance increased the rate of tuberculosis case detection and early treatment initiation.  

“WHO recommends that any intensified case finding strategy should consider the accuracy of the screening algorithm, the epidemiology of tuberculosis in the targeted group, and the availability, feasibility and cost of the diagnostic tests,” Gregory L. Calligaro, MD, from the division of pulmonology at the University of Zimbabwe College of Health Sciences, and the University of Cape Town Lung Institute, and colleagues wrote. “But, little high-quality evidence is available to inform decision-making around community-based intensified case finding strategies in high-burden countries, particularly in sub-Saharan Africa.”

Researchers performed a multicenter, randomized trial to compare novel diagnostic tools — including the rapid molecular Xpert-MTB/RIF (Cepheid) assay and, if HIV–infected, the Determine TB LAM (Alere) urine test — with routine, laboratory-based sputum smear microscopy for intensified case finding in communities with high TB and HIV prevalence in Cape Town, South Africa, and Harare, Zimbabwe. Calligaro and colleagues randomly assigned participants to either group, using culture as the reference standard. In South Africa, testing was done at the point of contact using a mobile van, whereas participants in Zimbabwe were transported to a clinic to be tested.

The primary endpoint in the study was the proportion of culture-positive TB cases initiating treatment at 60 days.

Out of 2,261 individuals screened between Oct. 18, 2013, and March 31, 2015, only 39% met the criteria for diagnostic testing. Of these 875 participants, the researchers assigned 439 to the novel group and 436 to the routine group. They confirmed that 74 (9%) of the participants had TB.

In the novel diagnostic group, 53% more participants started therapy than in the routine group. In the novel group, more patients with culture-positive TB were initiated on treatment at 60 days if researchers excluded late culture-based treatment initiation. Based on the rapid screening tests, patients with TB were started on treatment with Xpert 29% more than with routine smear examination (95% CI, 9-50; P = .0047). Calligaro and colleagues only treated one culture-positive patient based on a positive LAM test alone.

“A novel diagnostic strategy using Xpert resulted in faster initiation of treatment and increased the proportion of patients initiating treatment compared with routine diagnostic testing,” they wrote. “Whether the improved diagnostic lead-time reduced tuberculosis transmission or improves clinical outcome requires further study.”

In an associated commentary, Anete Trajman, MD, PhD, from the Social Medicine Institute at the State University of Rio de Janeiro in Brazil, and Frank Cobelens, MD, MSc, PhD, from the Amsterdam Institute for Global Health and Development at the Academic Medical Center, the Netherlands, wrote that the cost-effectiveness of novel diagnostic testing needs to be addressed. A screening algorithm based on Xpert can detect more TB cases earlier than sputum smear examination and yield more patients who immediately begin treatment, but its affordability was not explored in the study.

“Because of its high sensitivity, Xpert will probably detect more cases of tuberculosis in any setting, but how much more would the health system spend for each case additionally found?” they wrote. by Savannah Demko

Disclosure: The researchers report no relevant financial disclosures.

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