Xpert MTB/RIF assay can be used on archived gastric aspirate and induced sputum samples for sensitive diagnosis of paediatric tuberculosis

Abstract

BackgroundTuberculosis (TB) in children is neglected, mainly due to lack of sensitive diagnostic tools. Recently Xpert MTB/RIF assay has revolutionized the diagnostic field, but its usefulness in pediatric TB has not been reported from India and no report is available on its use on long term archived samples.MethodsWe recruited 130 pediatric patients with probable intrathoracic tuberculosis and their gastric aspirate (GA) and induced sputum (IS) samples on 2 consecutive days were collected between January 2009 and December 2012. All samples (n = 520) were subjected to smear examination, BACTEC-MGIT culture and in-house multiplex PCR. An aliquot of each sample was stored at −80 °C and tested in Xpert MTB/RIF assay in 2013.ResultsSample wise and patient wise detection rate of smear microscopy was 4.4 % and 10 %, while for BACTEC-MGIT culture this rate was 24.4 % and 46.9 %, respectively. Of the 130 day 1 GA samples, 31.5 % and 27.7 % day 2 GA samples were culture positive. Only 17.7 % GA samples were positive on both days. Of the 130 IS samples collected on day 1 and day 2, 15.4 % and 23.1 % samples were culture positive. A combination of GA and IS yielded best results. Combining both GA and IS, the overall sensitivity of Xpert MTB/RIF on smear and culture positive samples was 95.6 %. In smear negative and culture positive samples its sensitivity was 62.5 %. The duration of sample storage impacted the Xpert MTB/RIF test performance (p = 0.0001). In smear positive samples stored for 650–849 days, its sensitivity was 85.7 % and 77.1 % for IS and GA samples which dropped to 33.3 % and 50 %, respectively, if stored for more than 1050 days.DiscussionConfirmatory diagnosis of tuberculosis particularly in children is a medical challenge. No laboratory or radiological test can reach to a satisfactory level of diagnostic sensitivity. However, in this study we foundthat combination of multiple samples and multiple diagnostic tests can give much better yield, though notoptimum. In present study, combination of 2 gastric aspirates (GA) and 2 induced sputum (IS) samples collected on two consecutive days, and tested on three diagnostic methods yielded a significantly high detection rate. Despite long term storage, the overall sensitivity of Xpert MTB/RIF on smear and -culture positive samples remained very high. But after storing these samples under subfreezing conditions thesensitivity of Xpert MTB/RIF decreased significantly. This is expected because even if the sample is smear and culture positive, the count of surviving mycobacteria goes down, after several years this count can reach to a undetectable level.ConclusionThis report shows that smear and culture positive samples stored at subfreezing conditions for several years can be used in the Xpert MTB/RIF assay, while maintaining appreciable diagnostic test sensitivity and specificity.

Performance of the G4 Xpert® MTB/RIF assay for the detection of Mycobacterium tuberculosis and rifampin resistance: a retrospective case-control study of analytical and clinical samples from high- and low-tuberculosis prevalence settings

“…In addition, we found high sensitivity and specificity for MTBc and RIF resistance detection that compared well to the previous versions of the assay [4]. Most published reports of Xpert assay performance were conducted using the previous versions of the assay; our findings represent one of the first large studies reporting G4 Xpert assay performance and add to the growing literature [19–22] in both high- and low-TB prevalence settings.…”

Gastric specimens for diagnosing tuberculosis in adults unable to expectorate in Rawalpindi, Pakistan

“…28 We reported an Xpert sensitivity of 83% using positive Xpert and/or culture as a reference standard, compared to a pooled sensitivity in GS of 78% using culture as the gold standard reported in a systematic review by Maynard et al, 29 and a sensitivity of 90.4% for all types of pulmonary specimens reported by Chang et al 30 The majority of the patients tested (78%) had a risk of DR-TB, and Xpert testing made rapid DST results available for RMP in 257/313 TB cases.…”

Performance of Xpert MTB/RIF Assay for Childhood Pulmonary Tuberculosis With Real World Evidence in China

“…For establishing a definitive diagnosis of childhood PTB, multiple or repeated decision-making tests (such as MTB culture, nucleic acid test or sequencing) on RTS are often required. The added diagnostic yield from combined tests seems much higher than repeated test [15][16], although this was not extensively assessed in our study. A study from South Africa suggested that the incremental increase in sensitivity from testing a second specimen was 27.8% for MTB/RIF in smear-negative cases [17].…”