Retrospective observational study of diagnostic accuracy of the Xpert® MTB/RIF assay on fiberoptic bronchoscopy sampling for early diagnosis of smear-negative or sputum-scarce patients with suspected tuberculosis.

Pierre Le Palud,Karine Campbell,Romain Magnier,Vincent Cattoir,Emmanuel Bergot,Brigitte Malbruny,Gérard Zalcman,Youssef Oulkhouir

doi:10.1186/1471-2466-14-137

Abstract

BackgroundFiberoptic bronchoscopy (FOB) is a useful diagnosis tool in low-burden countries for patients with suspected pulmonary tuberculosis (TB) who are smear-negative or sputum-scarce. This study sought to determine the accuracy of the Xpert® MTB/RIF (XP) assay using FOB samples.MethodsWe retrospectively reviewed clinical, radiological, and microbiological characteristics of 175 TB-suspected patients requiring diagnostic FOB (bronchial aspirate or bronchoalveolar lavage) with XP assay. Polymerase chain reaction (PCR) and smear microscopy (SM) performances were first compared to culture, then to the final diagnosis, established based on clinical or radiological evolution when cultures were negative.ResultsOf the total 162 included patients, 30 (18.5%) had a final diagnosis of pulmonary TB, with positive cultures reported in 23. As compared to culture, sensitivity and specificity values were 80.0% and 98.6% for the XP assay, and 25.0% and 95.8% for SM, respectively. As compared to final diagnosis, the corresponding performance values were 60.0% and 100.0% for the XP assay, and 16.7% and 95.5% for SM, respectively. The sensitivity of the XP assay was significantly higher than that of SM in both cases (p = 0.003 and p = 0.001). Concerning the final diagnosis, both XP assay and culture sensitivities were similar (60% vs. 66.7%). PCR assay enabled pulmonary TB to be diagnosed earlier in 13 more cases, compared to SM.ConclusionOur study has confirmed the clinical benefits provided by XP assay compared to SM for the early diagnosis of suspected pulmonary TB cases requiring FOB, on per procedure samples, especially in a low TB-burden country.

Highlights

Fiberoptic bronchoscopy (FOB) is a useful diagnosis tool in low-burden countries for patients with suspected pulmonary tuberculosis (TB) who are smear-negative or sputum-scarce
Patient characteristics From October 2009 to April 2013, 175 consecutive patients presenting with suspected active pulmonary TB underwent FOB with an Xpert® MTB/RIF assay using respiratory samples
It should be noted that 18, 9, and 80 patients had 1, 2, and 3 sputum samples, respectively, that were collected before FOB, with the number of Xpert® MTB/RIF assays performed on the sample ranging from 0 to 3 for each patient (0: 110 patients; 1: 21; 2: 22; 3: 9)

Summary

Introduction

Fiberoptic bronchoscopy (FOB) is a useful diagnosis tool in low-burden countries for patients with suspected pulmonary tuberculosis (TB) who are smear-negative or sputum-scarce. Fiberoptic bronchoscopy (FOB) is considered a good option for these cases that pose a diagnostic challenge [3], SM is still exhibiting low sensitivity on FOB samples, with 5-35% on bronchial aspirates (BA) and 10-30% on bronchoalveolar lavages (BAL) [4,5,6,7,8,9]. While mycobacterial culture remains the gold standard for laboratory diagnosis of TB, it requires 2–6 weeks to confirm a diagnosis. This results in delays in initiating appropriate treatment while waiting for this confirmation, except for cases where there is strong enough clinical suspicion to initiate a presumptive anti-TB therapy

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