Wellness on Wheels (WoW): Iterative evaluation and refinement of mobile computer-assisted chest x-ray screening for TB improves efficiency, yield, and outcomes in Nigeria

Background: Wellness on Wheels (WoW) is a model of mobile systematic TB screening of high-risk populations combining digital chest radiography with computer-aided automated interpretation and chronic cough screening to identify presumptive TB in communities, health facilities and prisons in Nigeria. Understanding how models are designed and refined over time helps others to anticipate technical and political challenges, replicate successful strategies, and avoid common mistakes. Methods: : We piloted and refined approaches in phased evaluations, recalibrating CAD4TB thresholds to balance TB yield and feasibility. Iterative data monitoring of screening volumes, risk mix, number needed to screen (NNS), number needed to test (NNT), sample loss, TB treatment initiation and outcomes. Risk factors for loss along the diagnostic cascade were identified and mitigation plans were implemented. Participants with high likelihood on CAD4TB (≥80) who tested negative on a single spot GeneXpert were followed-up. Results: : Gradual improvements included: achieving screening targets (64.0% to 70.5%), risk group inclusion (91.5% to 92.9%), on-site sample processing (84.3% to 86.1%), treatment initiation (86.7% to 90.8%), treatment success (70.6% to 83.2%), and NNT (8.2 to 7.6). However, expectoration by asymptomatic presumptive participants (≈85%) and HIV testing coverage (64.9%) remained suboptimal. Conclusion: Mobile computer-assisted digital chest x-ray and chronic cough screening with GeneXpert MTB/RIF testing is feasible, acceptable, efficient and high-yield when highest risk groups and key stakeholders are engaged, and operations evolve in real time to fix problems. CAD4TB scores should be used to identify people who need clinical diagnosis and/or longer-term follow-up for progression to TB disease.