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BMC Infect Dis. 2019 Apr 27;19(1):347. doi: 10.1186/s12879-019-3778-9.

Effect of two alternative methods of pooling sputum prior to testing for tuberculosis with genexpert MTB/RIF.

Author information

1
Woolcock Institute of Medical Research, 298 Kim Ma street, Ba Dinh district, Ha Noi, Vietnam. phuong.nguyen@sydney.edu.au.
2
Woolcock Institute of Medical Research, 298 Kim Ma street, Ba Dinh district, Ha Noi, Vietnam.
3
Faculty of Medicine and Health, The University of Sydney, Sydney, Australia.
4
Centre for Social Disease Control, Ca Mau, Vietnam.
5
National TB Control Program, Hanoi, Vietnam.
6
South Western Sydney Clinical School, University of NSW, Sydney, Australia.

Abstract

BACKGROUND:

Pooling sputum specimens is one potential strategy for reducing the cost of using Xpert MTB/RIF, a rapid polymerase chain reaction (PCR)-based test, for the diagnosis of pulmonary tuberculosis. We sought to compare the sensitivity of two alternative method of pooling.

METHODS:

Patients referred for assessment for TB, whose initial sputum was Xpert MTB positive, were recruited and their sputum specimens were pooled for analysis with sputum specimens that were Xpert MTB negative. Two alternative pooling strategies were employed: one in which the concentration of sample reagent (buffer) was maintained at 2:1 (standard), in accordance with the manufacturer's instructions, and another in which the concentration of sample reagent was reduced to 1:1.

RESULTS:

We tested 101 Xpert MTB positive sputum specimens. Among these, 96% of valid test results (95% confidence interval (CI) 89-99%) were positive using the "standard buffer method". Using the "reduced buffer pooling" method 94% of valid test results (95% CI 87-98%) were positive. McNemar's test for the difference in paired proportions did not reach statistical significance (Pā€‰=ā€‰0.56).

CONCLUSION:

We have confirmed that pooling of two sputum specimens for testing in a single cartridge is a valid method of reducing the number of cartridges required when using Xpert MTB to detect pulmonary tuberculosis. Two alternative pooling strategies tested here yielded similar results.

TRIAL REGISTRATION:

The present study was conducted within the Active Casefinding in Tuberculosis (ACT3) Trial. The ACT3 Trial had been registered with Australian and New Zealand Clinical Trials Register on 8th April, 2014. The trial registration number is ACTRN12614000372684 . (Retrospectively registered).

KEYWORDS:

Diagnostic test characteristics; Nucleic acid amplification; Sensitivity

PMID:
31029099
PMCID:
PMC6486971
DOI:
10.1186/s12879-019-3778-9
[Indexed for MEDLINE]
Free PMC Article

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