Optimising molecular diagnostic capacity for effective control of tuberculosis in high-burden settings

Abstract

The World Health Organization's 2035 vision is to reduce tuberculosis (TB) associated mortality by 95%. While low-burden, well-equipped industrialised economies can expect to see this goal achieved, it is challenging in the low- and middle-income countries that bear the highest burden of TB. Inadequate diagnosis leads to inappropriate treatment and poor clinical outcomes. The roll-out of the Xpert(®) MTB/RIF assay has demonstrated that molecular diagnostics can produce rapid diagnosis and treatment initiation. Strong molecular services are still limited to regional or national centres. The delay in implementation is due partly to resources, and partly to the suggestion that such techniques are too challenging for widespread implementation. We have successfully implemented a molecular tool for rapid monitoring of patient treatment response to anti-tuberculosis treatment in three high TB burden countries in Africa. We discuss here the challenges facing TB diagnosis and treatment monitoring, and draw from our experience in establishing molecular treatment monitoring platforms to provide practical insights into successful optimisation of molecular diagnostic capacity in resource-constrained, high TB burden settings. We recommend a holistic health system-wide approach for molecular diagnostic capacity development, addressing human resource training, institutional capacity development, streamlined procurement systems, and engagement with the public, policy makers and implementers of TB control programmes.

Molecular Bacterial Load Assay Concurs with Culture on NaOH-Induced Loss of Mycobacterium tuberculosis Viability

“…DNA is a very stable molecule which takes a long period to degrade after cell death and thus cannot be used as a marker of viability and for monitoring the bactericidal effect of anti-TB therapy (6). A DNA-positive test result in treatment follow-up specimens does not necessarily indicate the presence of viable bacilli and could mislead the assessment of treatment progress (4,(6)(7)(8). Unsuccessful attempts have been made to use propidium monoazide, a dye which penetrates and inactivates DNA from dead cells, so that tests like the Xpert/MTB RIF assay can detect viable M. tuberculosis bacilli and be used for treatment monitoring (9,10).…”

“…It is a reverse transcriptase quantitative PCR (RT-qPCR) that quantifies the M. tuberculosis load from patient sputum using the 16S rRNA gene as a reference gene. In contrast to culture, MBLA is rapid, sensitive, and specific and does not require an NALC-NaOH decontamination step (7). Unlike mRNA, which occurs in a low copy number and is exquisitely sensitive to degradation, the higher abundance and relative stability of rRNA make MBLA a more sensitive and robust test.…”

United Kingdom–East and Southern Africa Partnership at the Forefront of Developing the First Ever Test that Measures Patient Tuberculosis Burden in Hours

“…Unfortunately, M. tuberculosis takes weeks to grow, and this is too long for results to inform initial patient management decisions. 8 Discovered 136 years ago, and despite its shortcomings of low sensitivity and inability to distinguish between dead and viable bacteria, semiquantitative smear microscopy remains the most widely used test for TB diagnosis and treatment monitoring. 10 Microscopy is often unreliable for samples from children and HIV-positive patients who often have a low TB bacterial load.…”

“…Furthermore, culture is acutely sensitive to endogenous and exogenous contaminants, such as non-TB bacteria and fungi, which grow rapidly and cause false-positive time to culture positivity (TTP) results. 8,9 Consequently, a result from culture requires 3 extra confirmatory tests: (1) acid-fast microscopy to confirm acid-fast bacilli, (2) blood agar culture to rule out contamination, and (3) an antigen test, MPT64, to confirm the presence of M. tuberculosis. These extra tests consume more person-hours and increase the total cost associated with culturing.…”

Beyond the Numbers: Interpreting WHO's Global Tuberculosis Report 2016 to Inform TB Policy and Practice in the East African Community

“…This includes providing the required infrastructure and human resources to deliver the services 16 and investing in postregistration anti-TBdrug clinical trials and affordable diagnostic approaches.…”