Know your epidemiology: one lesson of many for GeneXpert roll-out

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Cepheid's GeneXpert rapid tuberculosis diagnostic unit.

The following is a guest blog post by Sophie Beauvais, of the  Global Health Delivery Project at Harvard University, and Chris Gilpin from the Stop TB Department of the World Health Organization (WHO) team leading the roll-out of the GeneXpert rapid TB diagnostic test. The post summarizes an ongoing virtual panel discussion on the feasibility of implementing the Xpert MTB/RIF in countries with limited resources.

One week into the GeneXpert online panel, discussion is highlighting the critical importance of understanding the local epidemiology for tuberculosis (TB), especially for multidrug-resistant TB (MDR-TB) and also for HIV-associated TB. Prioritizing these two risk groups in diagnostic algorithms that use the Xpert MTB/ RIF as the initial diagnostic test is a key message for the efficient integration of this new tool into existing health systems. But it is by no means the only key message.

For years health implementers in high endemic areas with limited resources have been struggling with the lack of a rapid and reliable diagnostic test for HIV-associated TB and MDR-TB. Hence, the endorsement of the fully-automated nucleic acid amplification test (NAAT) by the WHO in December 2010 has been welcomed with enthusiasm from both implementers and donors. This novel tool reliably detects TB DNA in sputum specimens in less than two hours with 94.4 percent sensitivity for the simultaneous detection of rifampicin resistance with 98.3 percent specificity. Along with the WHO endorsement, many questions have arisen as to how best integrate this technology along with existing TB diagnostic tools in countries, especially those most affected by the disease and with limited resources.

Since current diagnostic algorithms for TB diagnosis is mainly based on quality assured smear microscopy in low-resource settings, commented Daniela Cirillo – head of the Emerging Bacterial Pathogens Unit at the San Raffaele Scientific Institute in Milano, Italy – Xpert implementation should be gradual and not disturb the existing laboratory network.

For Mark Perkins – chief scientific officer at FIND, the non-profit organization that co-developed the GeneXpert assay and led the evaluation and demonstration studies – the first strategy question is whether Xpert should be used primarily to improve case detection or to screen for MDR-TB.

“For countries choosing to focus on MDR screening, then clearly the populations selected for testing would be different, as might be the locations of device placement,” Perkins noted. The sentiment at FIND is that all countries should have national capacity for reference-level testing using conventional culture-based methods, but that Xpert might obviate the need for the development of culture and bio-safety infrastructure at many regional, district and sub-district settings.

Cost is an obvious issue being discussed. Funding schemes and special pricing are being sought. Cepheid Cares, a program put together by the maker of Xpert with key nonprofits, offers the latter.

Placement of the test is another point of contention. The WHO stipulates that Xpert MTB/RIF is not a point-of-care test, and experts recommend placing it at intermediate-level laboratories within the TB laboratory network. But some, like Ed Nardell, a TB Infection Control specialist at Harvard, comment that to be really useful, “Xpert needs to be at the point of care.” Furthermore, Perkins shared that in Brazil some Xpert machines are going into health centers without laboratory capacity and being run by nurses, while in other countries like South Africa a substantial amount of regional or centralized testing is ongoing or planned. In his opinion, placement depends on where patients seek care, where the security and power is available for maintenance, and what obstacles exist to information flow.

Other discussion topics from participants hailing from Afghanistan, Ethiopia, or India to name a few, include adding inclusion criteria, the disposal of cartridges, the need for further testing for isoniazid, the impact of operational temperature on outcome, and the need for reliable power supply. They’re also sharing roll-out strategies and hopes for this potentially transformational technology.

The virtual panel discussion is ongoing until May 20 and is hosted on GHDonline.org, a free platform of expert-led communities with members from more than 1,500 organizations worldwide. All TB implementers and policy-makers are invited to join.

One thought on “Know your epidemiology: one lesson of many for GeneXpert roll-out

  1. Pingback: Electronic nose “smells” TB, competes with rats | Humanosphere

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