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. 2022 Feb;7(2):e007592.
doi: 10.1136/bmjgh-2021-007592.

Pooled testing of sputum with Xpert MTB/RIF and Xpert Ultra during tuberculosis active case finding campaigns in Lao People's Democratic Republic

Vibol Iem  1   2 , Phonenaly Chittamany  2 , Sakhone Suthepmany  2 , Souvimone Siphanthong  2 , Phitsada Siphanthong  2 , Silaphet Somphavong  3 , Konstantina Kontogianni  1 , James Dodd  1 , Jahangir Am Khan  4 , Jose Dominguez  5 , Tom Wingfield  6   7 , Jacob Creswell  8 , Luis E Cuevas  9
Affiliations

Pooled testing of sputum with Xpert MTB/RIF and Xpert Ultra during tuberculosis active case finding campaigns in Lao People's Democratic Republic

Vibol Iem et al. BMJ Glob Health. 2022 Feb.

Abstract

Introduction: Active case finding (ACF) of individuals with tuberculosis (TB) is a key intervention to find the 30% of people missed every year. However, ACF requires screening large numbers of individuals who have a low probability of positive results, typically <5%, which makes using the recommended molecular tests expensive.

Methods: We conducted two ACF surveys (in 2020 and 2021) in high TB burden areas of Lao PDR. Participants were screened for TB symptoms and received a chest X-ray. Sputum samples of four consecutive individuals were pooled and tested with Xpert Mycobacterium tuberculosis (MTB)/rifampicin (RIF) (Xpert-MTB/RIF) (2020) or Xpert-Ultra (2021). The agreement of the individual and pooled samples was compared and the reasons for discrepant results and potential cartridge savings were assessed.

Results: Each survey included 436 participants, which were tested in 109 pools. In the Xpert-MTB/RIF survey, 25 (sensitivity 89%, 95% CI 72.8% to 96.3%) of 28 pools containing MTB-positive samples tested positive and 81 pools containing only MTB-negative samples tested negative (specificity 100%, 95% CI 95.5% to 100%). In the Xpert-Ultra survey, all 32 (sensitivity 100%, 95% CI 89.3% to 100%) pools containing MTB-positive samples tested positive and all 77 (specificity 100%, 95% CI 95.3% to 100%) containing only MTB-negative samples tested negative. Pooling with Xpert-MTB/RIF and Xpert-Ultra saved 52% and 46% (227/436 and 199/436, respectively) of cartridge costs alone.

Conclusion: Testing single and pooled specimens had a high level of agreement, with complete concordance when using Xpert-Ultra. Pooling samples could generate significant cartridge savings during ACF campaigns.

Keywords: Xpert MTB/RIF; Xpert Ultra; active case finding; pooled testing; pooling.

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Conflict of interest statement

Competing interests: The authors have no conflicts of interest to declare.

Figures

Figure 1
Figure 1
Flow diagram of the sputum processing.
See this image and copyright information in PMC

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