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

Abstract IntroductionTuberculosis (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. MethodsData 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.ResultsA 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. ConclusionStatistically 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.