Iterative evaluation of mobile computer-assisted digital chest x-ray screening for TB improves efficiency, yield, and outcomes in Nigeria

Wellness on Wheels (WoW) is a model of mobile systematic tuberculosis (TB)
screening of high-risk populations combining digital chest radiography
with computer-aided automated detection (CAD) and chronic cough screening
to identify presumptive TB clients in communities, health facilities, and
prisons in Nigeria. The model evolves to address technical, political, and
sustainability challenges. Screening methods were iteratively refined to
balance TB yield and feasibility across heterogeneous populations.
Performance metrics were compared over time. Screening volumes, risk mix,
number needed to screen (NNS), number needed to test (NNT), sample loss,
TB treatment initiation and outcomes. Efforts to mitigate losses along the
diagnostic cascade were tracked. Participants with high likelihood on
CAD4TB (≥80) who tested negative on a single spot GeneXpert were
followed-up to assess TB status at six months. An experimental calibration
method achieved a viable CAD threshold for testing. High-risk groups and
key stakeholders were engaged. Operations evolved in real-time to fix
problems. Incremental improvements in mean client volumes (128 to
140/day), target group inclusion (92% to 93%), on-site testing (84% to
86%), TB treatment initiation (87% to 91%), and TB treatment success (71%
to 85%). Attention to those as highest risk boosted efficiency (the NNT
declined from 8.2 ± SD8.2 to 7.6 ± SD7.7). Clinical diagnosis was added
after follow-up among those with ≥ 80 CAD scores initially spot-sputum
negative found 11 additional TB cases (6.3%) after 121 person-years of
follow-up. Iterative adaptation in response to performance metrics foster
feasible, acceptable, and efficient TB case-finding in Nigeria. High CAD
scores can identify subclinical TB and those at risk of progression to
bacteriologically-confirmed TB disease in the near term. Policy makers,
donors, and community advocates are hesitant to invest in the steep
infrastructure costs for mobile digital chest x-ray and GeneXpert MTB/RIF
(dCXR/GXP) laboratories without a better understanding of how to maximize
and sustain their impact. It is rarely possible to conduct the months of
local CAD calibration recommended by experts via costly universal testing
with a reference standard.4,9 Stakeholder needs and resource limitations
require a more rapid and cost-conscious means of setting a sustainable
algorithm. Viable, field-robust methodologies are needed, and optimization
strategies informed by routine field findings were lacking. A precise
assessment of the contribution of routine mobile TB screening has been
challenging because few authors fully disaggregate losses along the
diagnostic cascade or track TB treatment outcomes. Publication bias has
limited access to results of active case finding pilots with suboptimal
risk group targeting, community engagement, yield, or treatment
outcomes.10–14 Evaluations (and scrutiny) of routine data are needed that
make the demands, constraints, costs and choices facing implementers more
explicit.