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Comparative Study
. 2019 Jun 13:33:110.
doi: 10.11604/pamj.2019.33.110.15319. eCollection 2019.

The effect of sputum quality and volume on the yield of bacteriologically-confirmed TB by Xpert MTB/RIF and smear

Onani Zimba  1 , Tsaone Tamuhla  2 , Joyce Basotli  1 , Gaoraelwe Letsibogo  3 , Sherri Pals  4 , Unami Mathebula  1 , Anikie Mathoma  1 , Christopher Serumola  1 , Kitso Ramogale  2 , Rosanna Boyd  1   5 , Tiffany Tran  1 , Alyssa Finlay  1   5 , Andrew Auld  4 , Anand Date  4 , Heather Alexander  4 , Violet Chihota  6   7 , Tefera Agizew  1   7   8
Affiliations
Comparative Study

The effect of sputum quality and volume on the yield of bacteriologically-confirmed TB by Xpert MTB/RIF and smear

Onani Zimba et al. Pan Afr Med J. .

Abstract

Introduction: The World Health Organization endorsed (2010) the use of Xpert MTB/RIF and countries are shifting from smear microscopy (smear)-based to Xpert MTB/RIF-based tuberculosis (TB) diagnostic algorithms. As with smear, sputum quality may predict the likelihood of obtaining a bacteriologically-confirmed TB when using Xpert MTB/RIF.

Methods: From 08/12-11/2014, all people living with HIV were recruited at 22 clinics. For patients screened positive using the four TB symptoms their sputa were tested by Xpert MTB/RIF and smear. Laboratorians assessed and recorded sputum appearance and volume. The yield of bacteriologically-positive sputum evaluated using Xpert MTB/RIF and smear, likelihood-ratios were calculated.

Results: Among 6,041 patients enrolled 2,296 were presumptive TB, 1,305 (56.8%) had > 1 sputa collected and 644/1,305 (49.3%) had both Xpert MTB/RIF and smear results. Since >1 sputa collected from 644 patients 954 sputa were tested by Xpert MTB/RIF and smear. Bacteriologically-positive sputum was two-fold higher with Xpert MTB/RIF 11.4% versus smear 5.3%, p < 0.001. Sputum appearance and quantity were not predictive of bacteriologically-positive results, except volume of 2ml to < 3ml, tested by Xpert MTB/RIF LR+= 1.26 (95% CI, 1.05-1.50).

Conclusion: Xpert MTB/RIF test yield to bacteriologically-positive sputum was superior to smear. Sputum quality and quantity, however, were not consistently predictive of bacteriologically-positive results by Xpert MTB/RIF or smear.

Keywords: Botswana; Molecular diagnostic yield; sputum quality.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Patients enrolled, screened for tuberculosis symptoms and tested by Xpert MTB/RIF and smear
Figure 2
Figure 2
Proportion of salivary sputum by study sites
See this image and copyright information in PMC

References

    1. World Health Organization Monitoring of Xpert MTB/RIF roll-out. Accessed on 21 July 2017.
    1. National Tuberculosis Program Manual . Ministry of Health. Botswana; 2011.
    1. Ho J, Marks GB, Fox GJ. The impact of sputum quality on tuberculosis diagnosis: a systematic review. Int J Tuberc Lung Dis. 2015 May;19(5):537–44. - PubMed
    1. World Health Organizations . Quality assurance of sputum microscopy in DOTS Programmes, 2003. Regional Office for the Western Pacific; ISBN 92 9061 056 5. Accessed on 21 July 2017.
    1. Technical guide: sputum examination for tuberculosis by direct microscopy in low income countries. Fifth edition. Paris, France: Int Union of TB and Lung Dis; 2000.

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