Exploring trade-offs in diagnostic algorithm, population coverage, and duration of community screening for tuberculosis
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Background
Current tuberculosis (TB) prevention and care strategies have failed to reduce disease burden at the pace required to meet global targets. Community screening may enable more rapid declines in TB burden, but evidence is mixed. We used mathematical modelling to evaluate trade-offs in diagnostic algorithm, population coverage, and duration of screening.
Methods and Findings
Our model recognises symptomatic infectious TB (sTB), asymptomatic infectious TB (aTB), and non-infectious TB (nTB) and was calibrated to infectious TB (sTB+aTB) prevalences of 1,000, 500, and 250 per 100,000 population. We modelled algorithms targeting three disease thresholds: sTB (by prolonged cough with confirmatory GeneXpert Ultra), infectious TB (by GeneXpert Ultra), or all TB (sTB+aTB+nTB, by chest X-ray) with different levels of population coverage and duration. We estimated reductions in sTB incidence and TB mortality up to 10 years after the start of screening.
Maximum coverage (100%) and duration (five rounds) was projected to reduce sTB incidence by 26.9% (22.8-31.5%) with the algorithm targeting sTB and 74.0% (68.5-79.1%) with the algorithm targeting infectious TB for baseline prevalence of 500 per 100,000. However, incidence rebounded at the end of screening, erasing 9.8% and 15.9%, respectively, of those reductions within five years. The algorithm targeting all TB showed higher potential for rapid reductions – over 98% – with negligible rebound if all individuals with nTB were reached; however, low diagnostic accuracy of current tools led to prohibitive overdiagnosis, with 7.2 false positives per true positive in a single round of screening targeting all TB. Screening algorithms targeting lower disease thresholds generally achieved greater impact with lower population coverage and/or duration. Findings were broadly similar for mortality and across baseline prevalences.
Conclusion
Our work highlights opportunities for community screening to achieve the substantial reductions in TB morbidity and mortality required to end TB with approaches that balance diagnostic algorithm, population coverage, and duration of screening.
