Swab testing could find more TB cases at low extra cost

Diagnosing tuberculosis usually relies on patients producing sputum, but Tongue swabs (TS) offer a promising alternative for molecular testing. As part of the Tongue Swab Yield (TSwaY) study, researchers led by Florian M. Marx assessed whether switching to or adding TS-based testing could be practical and affordable in primary healthcare settings. The team collected cost data and measured how many people with TB would be detected when using a new device, MiniDock MTB (Guangzhou Pluslife Biotech Co., Ltd., China), compared with current practice. The work focused on four high-burden countries: the Philippines, Uganda, Vietnam, and Zambia. By comparing different ways to use TS — replacing sputum testing entirely, adding TS only for people who cannot produce sputum, or adding TS for people whose sputum tests are negative or unclear — the study set out to show not just whether TS can find more cases, but how much it would cost health services to do so. The study was supported by the Gates Foundation.

Cost data came from primary healthcare facilities in the Philippines, Uganda, Vietnam, and Zambia. The team evaluated three MiniDock MTB strategies: (1) TS-only, replacing sputum Xpert Ultra; (2) limited combined, with Xpert Ultra first-line and TS added for sputum-scarce individuals; and (3) extended combined, with TS also added for those with negative or indeterminate sputum results. They also simulated an integrated combined strategy using MiniDock MTB to test sputum swabs (if available) and TS for sputum-scarce individuals. Incremental cost-effectiveness ratios (ICERs) were estimated relative to the next least costly strategy, and net monetary benefits (NMB) were evaluated across willingness-to-pay (WTP) thresholds. Best estimates used observed diagnostic yield with 95% uncertainty intervals from probabilistic simulation. Among 1,370 participants, TS-only was least costly but produced the fewest diagnoses: 62 (95% UI: 48;75) at USD 300 (95% UI: 244;388) per diagnosis. The standard of care, sputum Xpert Ultra, was extendedly dominated by TS-based strategies. Limited combined yielded 12 (95% UI: -1;22) additional diagnoses at an incremental USD 1,507 per diagnosis compared with TS-only; extended combined yielded 15 (95% UI: 8;22) additional diagnoses at an incremental USD 1,004 (95% UI: 661;1,655) per diagnosis compared with limited combined. The simulated integrated combined sputum swab and TS testing using MiniDock MTB had the highest NMB at WTP thresholds above USD 161 per additional diagnosis.

Taken together, these findings suggest that integrating swab-based testing with MiniDock MTB into diagnostic algorithms in high-burden settings can increase tuberculosis case detection at minimal additional cost. Choosing TS-only will save money but detect fewer cases, while limited and extended combined strategies identify more people with TB for additional incremental cost per diagnosis. Importantly, the standard approach of sputum Xpert Ultra was not the most efficient option in this study, being extendedly dominated by strategies that include TS. The simulated integrated combined approach — testing sputum swabs when available and using TS for sputum-scarce individuals with MiniDock MTB — showed the best balance of cost and benefit when health systems are willing to pay more than USD 161 per extra diagnosis. For policymakers and clinics in the Philippines, Uganda, Vietnam, and Zambia, these results provide evidence to consider updating testing algorithms to include TS-based testing to find more patients without large increases in spending.