Identifying TB hotspots through mobile x-rays in Karachi, Pakistan: Spatial analysis of data from an active case-finding program

Document Type



Community Health Sciences


Introduction: Tuberculosis (TB) is the leading cause of avoidable deaths from an infectious disease globally and a large of number of people who develop TB each year remain undiagnosed. Active case-finding has been recommended by the World Health Organization to bridge the case-detection gap for TB in high burden countries. However, concerns remain regarding their yield and cost-effectiveness.
Methods: Data from mobile chest X-ray (CXR) supported active case-finding community camps conducted in Karachi, Pakistan from July 2017- March 2020 was retrospectively analyzed. After a CXR screening supported by computer-aided detection, those with presumptive TB were counselled to submit a sputum sample for Xpert MTB/RIF testing. Frequency analysis was carried out at the camp-level and outcomes of interest for the spatial analyses were mycobacterium TB positivity (MTB+) and X-ray abnormality ratios. The Moran’s I statistic was used to test for spatial autocorrelation for MTB+ and abnormal X-rays within Union Councils (UCs) in Karachi. Local Indicators of Spatial Autocorrelation analyses were performed for UCs within Karachi. Point-pattern analyses were carried out utilizing GPS coordinates recorded at the camp sites and were analyzed for spatial autocorrelation using Getis Ord Star tests.
Results: A total of 1,161 (78.1%) camps yielded no MTB+ cases, 246 (16.5%) camps yielded 1 MTB+, 52 (3.5%) camps yielded 2 MTB+ and 27 (1.8%) yielded 3 or more MTB+. A total of 79 (5.3%) camps accounted for 193 (44.0%) of MTB+ cases detected. Statistically significant clustering for MTB positivity (Moran’s I: 0.09) and abnormal chest X-rays (Moran’s I: 0.36) ratios was identified within UCs in Karachi. Clustering of UCs with high MTB positivity were identified in Karachi West district. Clusters of camp locations with high MTB+ ratios were identified in Karachi South and Karachi West districts and in several locations in the north and eastern peripheries of the city.
Conclusion: Statistically significant spatial variation was identified in yield of bacteriologically positive TB cases and in abnormal CXR through active case-finding in Karachi. Cost-effectiveness of active case-finding programs can be improved by identifying and focusing interventions in hotspots and avoiding locations with no known TB cases reported through routine surveillance.


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