resistant tb, detected

too far from care

Problem statement

Approximately 500,000 people develop drug-resistant tuberculosis each year, yet only one-third are diagnosed and enrolled on appropriate treatment. The gold-standard method — culture-based phenotypic drug susceptibility testing (DST) — takes 2-6 weeks, requires BSL-3 laboratory infrastructure, and is unavailable at the peripheral health facilities where most patients first present. GeneXpert MTB/RIF detects only rifampicin resistance, providing no guidance for selecting alternative regimens when resistance to isoniazid, fluoroquinolones, or newer drugs like bedaquiline is present. The result: most patients with drug-resistant TB are either never diagnosed or are treated with ineffective regimens for weeks before resistance is identified.

Why this matters

Drug-resistant TB kills approximately 150,000 people per year. MDR-TB treatment takes 9-18 months and costs 10-100x more than drug-susceptible TB treatment. Delayed or incorrect treatment drives ongoing transmission of resistant strains, creating a positive feedback loop. The WHO TPP identifies four priority drugs for peripheral DST — rifampicin, isoniazid, fluoroquinolones, and bedaquiline — because knowing resistance status for these four enables selection of the appropriate treatment regimen. No existing test covers all four at the peripheral level.

What’s been tried and why it hasn’t worked

GeneXpert MTB/RIF (2010) was a breakthrough for rifampicin resistance detection but tests only one drug. GeneXpert MTB/XDR (2021) expands coverage to isoniazid, fluoroquinolones, and second-line injectables with ~93% sensitivity and 98% specificity for fluoroquinolone resistance, but runs on the same infrastructure-dependent platform. Whole genome sequencing offers comprehensive resistance profiling but costs >$100/test, requires specialized equipment, and has incomplete knowledge of resistance mutations for newer drugs. Line probe assays (Hain GenoType) cover first- and second-line drugs but require BSL-3 facilities and trained molecular biologists. Critically, none of these approaches delivers results fast enough for same-day treatment decisions: the WHO TPP optimal target is <30 minutes for detection plus DST.

What would unlock progress

Two approaches show promise: (1) microfluidic chip-based phenotypic DST, which has demonstrated growth-based resistance detection in 12 hours for seven drugs including bedaquiline and levofloxacin, and (2) targeted next-generation sequencing panels that could cover all priority resistance mutations on a portable platform. The WHO TPP sets the bar: instrument cost <$5,000 (optimal), time to result <30 minutes (optimal) or <6 hours (minimum), deployable at peripheral health centers. Bridging this gap requires simultaneous advances in microfluidics, sample processing, and cost reduction.

Entry points for student teams

A team could prototype a microfluidic DST chip optimized for the four WHO priority drugs, using fluorescence-based readout of mycobacterial growth in drug-containing vs. drug-free chambers, with the key engineering challenge being reduction of incubation time from 12 hours to <6 while maintaining sensitivity — but developed on a surrogate organism rather than M. tuberculosis: Mycobacterium smegmatis mc(2)155 (ATCC 700084, biosafety level 1) for the fluidics, growth readout and time-to-detection work, or M. tuberculosis variant bovis BCG (ATCC 35734, biosafety level 2) where a slow-growing complex member matters. Confirmation on clinical M. tuberculosis isolates is the one step a student team cannot do for itself — it needs BSL-3 containment and banked patient isolates, held by national TB reference laboratories, the WHO supranational reference laboratory network, and the handful of universities with mycobacteriology BSL-3 cores — so the semester deliverable is a characterized chip plus the validation protocol written for such a lab. A second door needs no laboratory at all: design the targeted sequencing panel for rifampicin, isoniazid, fluoroquinolone and bedaquiline resistance and validate it in silico against genuinely public data — WHO's Catalogue of mutations in Mycobacterium tuberculosis complex and their association with drug resistance, 2nd ed. (2023) publishes graded mutation–resistance associations as a free downloadable spreadsheet, and the CRyPTIC consortium's reuse table (`ftp.ebi.ac.uk/pub/databases/cryptic/release_june2022/reuse/`) pairs isolate genotypes with measured MICs across 13 drugs, together enough to compute the panel's sensitivity, name its coverage gaps for bedaquiline, and benchmark cost and turnaround against GeneXpert XDR. Relevant disciplines: microfluidics, biomedical engineering, molecular biology, bioinformatics.