Pooled testing expands rapid TB diagnosis in Cameroon

Tuberculosis remains difficult to diagnose quickly and affordably in many places: by 2024 only 54% of people with TB had an initial molecular diagnostic test, in part because of high test costs. To address that gap, Cameroon adopted pooled testing as a way to stretch limited supplies of the Xpert MTB/RIF Ultra (Ultra) assay and reach more people. Pooled testing combines sputum specimens from several individuals into a single test; if the combined sample is negative, everyone in the pool is reported negative, and if it is positive each specimen is retested individually. The World Health Organization has recently recommended pooled testing to expand access to molecular diagnostics when resources are constrained. In a retrospective evaluation led by corresponding author Ngha Ndze Mbuh, researchers reviewed Ultra testing performed at GeneXpert laboratories that used both individual and pooled approaches. Laboratory staff decided whether to test samples individually or in pools of 2 to 8 based on locally available information such as smear microscopy results, lab positivity rates, daily testing volume, availability of Ultra cartridges and GeneXpert modules, and patient characteristics. The team extracted test results and run durations directly from GeneXpert instruments to compare efficiency, time to result, and assay cost.

The evaluation covered Oct 2023 to Mar 2025 across 16 GeneXpert laboratories and a total of 71,328 sputum specimens. Of those, 59,164 specimens were tested in pools, and 1,999 pooled specimens (3.4%) had TB detected. For the pooled specimens the laboratories used 20,838 Ultra cartridges, which works out to 0.35 cartridges per result — a substantial reduction compared with individual testing. The pooled strategy enabled an additional 38,326 people to have molecular test results compared with a scenario in which every specimen would have been tested individually. Time to result was also faster for pooled specimens: average times ranged from 45 minutes for specimens in pools of 2 down to 10 minutes for specimens in pools of 8, compared with 66 minutes for individual testing. Calculated assay cost per result fell to $2.81 for specimens tested in pools overall, with costs ranging from $5.29 for pools of 2 to $1.19 for pools of 8, compared with $7.97 per result for individual testing.

This large-scale, programmatic experience shows that pooled testing on the Xpert MTB/RIF Ultra assay can meaningfully expand access to molecular TB diagnosis when supplies and instrument capacity are limited. By reducing the number of Ultra cartridges needed per result, pooled testing in Cameroon allowed laboratory networks to deliver tens of thousands more test results without additional cartridges or modules. Faster instrument time to result for pooled specimens — especially in larger pools — could reduce delays in reporting and help clinics prioritize patients who need further follow-up. The implementation relied on laboratory staff using local information, such as smear microscopy and lab positivity rates, to decide when and how large pools should be, demonstrating a flexible approach that can be adapted to local conditions. As the first large-scale report of operational pooled testing for TB, these findings support wider uptake by national TB programs and laboratories as a practical way to increase molecular testing coverage when resources are constrained.