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

Abstract

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 tuberculosis attending primary health care or general hospital facilities in Alagoas, Brazil. The 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: A total of 396 participants were tested. A total of 95 (24.0%) individual samples were Mycobacterium tuberculosis (MTB)-positive, 300 (75.8%) "MTB not detected", including 20 "MTB trace", and one reported an error. A total of 99 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 between individual and pooled testing was 96.0%. Pooling had a sensitivity of 95.0% (95% confidence interval 86.9-99%), specificity of 97.1% (95% confidence interval 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. The pooling of samples for testing improves the efficiency of testing, potentially enabling the screening and testing of larger numbers of individuals more cost-effectively.

Keywords: Brazil; Diagnosis; Pooling samples; Tuberculosis; Xpert Ultra.