Implementation of pooled testing of sputum specimens from multiple individuals for rapid molecular detection of tuberculosis in Cameroon: retrospective evaluation of efficiency, cost, and instrument time to result

BackgroundOnly 54% of people with TB had an initial molecular diagnostic test in 2024, due to barriers including high test costs. Pooled testing is implemented in Cameroon as a strategy to increase testing efficiency on the Xpert MTB/RIF Ultra (Ultra) assay and extend molecular testing to more people when test reagents are limited, as recently recommended by the World Health Organization. At GeneXpert sites, laboratory personnel decide whether to test individually or in pools and pool size based on locally available information, including smear microscopy results, lab positivity rates, daily testing volume, availability of Ultra cartridges and GeneXpert modules, and patient characteristics. MethodsWe conducted a retrospective evaluation of Ultra testing at GeneXpert laboratories that implemented both individual and pooled testing in pools of 2 to 8. Ultra test results and duration were extracted from GeneXpert instruments. Testing efficiency, instrument time to result, and assay cost were analyzed overall and by pool size. ResultsFrom October 2023 to March 2025, 71,328 sputum specimens were tested at 16 GeneXpert laboratories. For 59,164 specimens tested in pools, including 1,999 (3.4%) with TB detected, 20,838 Ultra cartridges were used, or 0.35 cartridges per result, enabling an additional 38,326 people to have molecular test results compared to if specimens were tested individually. The average time to result varied from 45 minutes to 10 minutes for specimens tested in pools of 2 or 8, respectively, as compared to 66 minutes for individual testing. The calculated assay cost per result was $2.81 for specimens tested in pools (from $5.29 to $1.19 for specimens in pools of 2 or 8, respectively) as compared to $7.97 for individual testing. DiscussionImplementation of pooled testing enabled many more people to have a molecular test result for TB, with significant time and cost savings compared to individual testing. What is already known on this topicPooled testing is a strategy used to increase testing efficiency by combining specimens from multiple individuals prior to testing; if the pool tests negative, a negative result is reported for each specimen with no further testing, and if the pool tests positive, then each specimen from the pool is re-tested individually and the individual result is reported. The World Health Organization has recently recommended the use of pooled testing to increase access to molecular diagnostic testing for tuberculosis when resources are constrained. What this study addsThis is the first report of large-scale programmatic implementation of pooled testing for the detection of TB. Pooled testing was performed by laboratory personnel who decided whether to test individually or in pools of size 2 to 8, based on the information available to them. Implementation of pooled testing enabled many more people to be tested with existing resources, with significant reductions in time to result and assay cost per specimen tested. How this study may affect research, practice or policyThis demonstration of the successful scale up of pooled testing for TB should contribute to uptake of pooled testing by national TB programs and laboratories to increase access to molecular testing for TB when resources are constrained.