Pooling of sputum samples to increase tuberculosis diagnostic capacity in Brazil during the COVID-19 pandemic

Objectives

We assessed whether combining (pooling) four individual's samples and testing with Xpert Ultra has the same accuracy as testing samples individually, as a more efficient testing method.

Methods

We conducted a cross-sectional study of individuals with presumptive TB attending primary health care or general hospital facilities in Alagoas, Brazil. Sputum samples of four consecutive individuals were pooled and the pool and individual samples were tested with Xpert Ultra. The agreement of the tests was compared using kappa statistics. We estimated the sensitivity and specificity of pooling using the individual test as the reference standard and potential cartridge savings.

Results

Three hundred and ninety-six participants were tested. Ninety-five (24.0%) individual samples were MTB-positive, 300 (75.8%) MTB-not detected, including 20 MTB-trace, and one reported an error. Ninety-nine pools of four samples were tested, of which 62 (62.6%) had MTB-detected and 37 (37.4%) MTB-not detected, including six (6.1%) with MTB-trace. The agreement of individual and pooled testing was 96.0%. Pooling had sensitivity of 95.0% (95%CI 86.9%–99%), specificity of 97.1% (95%CI 85.1%–99.9%) and Kappa of 0.913. The method saved 12.4% of cartridge costs.

Conclusion

The pooled testing of specimens had a high level of agreement with individual testing. Pooling of samples for testing improves the efficiency of testing, potentially enabling the screening and testing of larger numbers of people more cost-effectively.