Sputum quality and diagnostic performance of GeneXpert MTB/RIF among smear-negative adults with presumed tuberculosis in Uganda
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Date
2017
Journal Title
Journal ISSN
Volume Title
Publisher
PLoS ONE
Abstract
Introduction of GeneXpert MTB/RIF (Xpert) assay has constituted a major breakthrough for
tuberculosis (TB) diagnostics. Several patient factors may influence diagnostic performance
of Xpert including sputum quality.
Objective
We carried out a prospective, observational, cross-sectional study to determine the effect of
sputum quality on diagnostic performance of Xpert among presumed TB patients in Uganda.
Methods
We collected clinical and demographic information and two sputum samples from participants.
Staff recorded sputum quality and performed LED fluorescence microscopy and
mycobacterial culture on each sample. If both smear examinations were negative, Xpert
testing was performed. We calculated diagnostic yield, sensitivity, specificity, and other indicators
for Xpert for each stratum of sputum quality in reference to a standard of mycobacterial
culture.
Results
Patients with salivary sputum showed a trend towards a substantially higher proportion of
samples that were Xpert-positive (54/286, 19%, 95% CI 15±24) compared with those with all other sputum sample types (221/1496, 15%, 95% CI 13±17). Blood-stained sputum produced
the lowest sensitivity (28%; 95% CI 12±49) and salivary sputum the highest (66%;
95% CI 53±77). Specificity didn't vary meaningfully by sample types. Salivary sputum was
significantly more sensitive than mucoid sputum (+13%, 95% CI +1 to +26), while bloodstained
sputum was significantly less sensitive (-24%, 95% CI -42 to -5).
Conclusions
Our findings demonstrate the need to exercise caution in collecting sputum for Xpert and in
interpreting results because sputum quality may impact test yield and sensitivity. In particular,
it may be wise to pursue additional testing should blood-stained sputum test negative
while salivary sputum should be readily accepted for Xpert testing given its higher sensitivity
and potentially higher yield than other sample types. These findings challenge conventional
recommendations against collecting salivary sputum for TB diagnosis and could inform new
standards for sputum quality.
Description
Keywords
Sputum quality, GeneXpert MTB/RIF, Smear-negative adults, Tuberculosis
Citation
Meyer AJ, Atuheire C, Worodria W, Kizito S, Katamba A, Sanyu I, et al. (2017) Sputum quality and diagnostic performance of GeneXpert MTB/RIF among smear-negative adults with presumed tuberculosis in Uganda. PLoS ONE 12(7): e0180572. https://doi.org/10.1371/journal. pone.0180572