Community-wide TB screening likely helps more than it harms

Tuberculosis remains a global public health challenge, and community-wide screening is one of the key strategies proposed to find people with disease early. But a frequent worry is overtreatment: if screening tests produce false positive results, some people might receive unnecessary treatment and experience avoidable side effects. Rein M G J Houben led a re-evaluation of that concern by examining how decisions about whom to screen and how to judge test results change the balance of benefit and harm. The researchers focused on adult pulmonary TB and on different prevalence thresholds for starting community-wide screening: a prevalence threshold of 0.5% (the current global standard), a lower 0.25% threshold, and a very low 0.1% threshold. They also revisited the standards used to define a true case of TB, recognizing limitations in current reference standards and the consequences those limits have for calculating test performance, screening coverage, and treatment decisions. Rather than assuming a single definition, the team compared outcomes using multiple reference approaches to better understand real-world trade-offs.

To quantify benefits and harms the study estimated coverage of community-wide screening at the three prevalence thresholds and assessed test performance for Xpert Ultra against multiple reference standards: sputum culture, plus clinical evaluation, plus disease progression within two years. Potential harm was measured using disability adjusted life years (DALYs) that would be incurred or averted by treatment or non-treatment. The analysis reported net specificity, positive predictive value (PPV), the ratio of false positives to true positives, and DALYs averted for treatment decisions based on each reference standard. Lowering the screening threshold increased coverage of the global TB burden from the current 42% to 84% at 0.25% and 89% at 0.1%. In a model population of 100,000 with 0.5% prevalence, community screening specificity was 99.5%, rising to 99.7% when using disease progression as the reference standard, and PPV rose from 45% to 66%. Importantly, estimated harm from withholding appropriate treatment was roughly 1,200 times higher than harm from providing inappropriate treatment, and initiating treatment after a positive Xpert Ultra increased overall DALYs averted (median 5,977 versus 3,750).

Taken strictly from these results, the balance of evidence favors treating people who test positive on a molecular test like Xpert Ultra in community-wide screening programs. The study suggests that the potential harms from a degree of overtreatment are small compared with the much larger harms of failing to treat genuine TB disease. It also shows that lowering the prevalence threshold for screening would substantially expand coverage and could reach most of the global TB burden, but that how we define a true TB case matters: using disease progression as a reference standard improves apparent test specificity and positive predictive value. The authors conclude that simplified, expanded community-wide screening paired with active treatment after positive molecular tests is likely to avert more disability and death than it causes harm, supporting a push to widen screening while continuing careful clinical evaluation and follow-up.