Evaluation of Abbott RealTime MTB detection and RIF/INH resistance assay for direct detection of mycobacterium tuberculosis and drug resistance in respiratory specimen

Abstract

Tuberculosis (TB) is one of the top ten causes of death for infectious disease worldwide, and the emergency of multi-drug resistant tuberculosis (MDR-TB) constitutes a serious threat to public health in the world. Rapid and accurate detection of Mycobacterium tuberculosis (MTB) and antibiotics susceptibility have taken a more important role in the TB laboratory. This study aimed to verify the diagnostic performance of Abbott RealTime MTB assay (Abbott-RT) according to manufacturer’s claim and to compare the performance with an in-house single-tube nested IS6110 real-time PCR by using MTB culture as the reference standard. The genotypic RIF and INH resistance markers of all “MTB detected” specimens in Abbott-RT were further identified by Abbott RIF/INH Resistance Assay (Abbott-RIF/INH) in reflex mode and the results were compared with the DST results from The Public Health Laboratory Centre of Department of Health (PHLC). Any discordant result between Abbott-RIF/INH and phenotypic DST was confirmed and resolved by Sanger sequencing. A total 106 respiratory samples were collected retrospectively in the Kowloon West Cluster (KWC) in Hong Kong based on the CobasTaqman result from April to September 2016 for the evaluation of Abbott RealTime MTB Detection and RIF/INH Resistance Assay. All specimens were subjected to AFB smear microscopy and AFB culture. Among the 106 respiratory specimens, 53 specimens were MTB culture positive and 53 specimens were MTB culture negative in this study. Abbott-RT successfully detected MTB complex (MTBC) in 53/53 (100%) confirmed MTB positive specimens. The 53/53 (100%) confirmed MTB negative cases were all reported as “MTBC not detected” by Abbott-RT. All results from Abbott-RT assay correlated with the identification result of PHLC. The overall sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of Abbott-RT were 100%. Abbott-RT also demonstrated no cross reactivity with non-tuberculous Mycobacteria (NTM) and reported “MTBC not detected” to all NTM specimens. No PCR inhibition was observed in the evaluation.

All 53 reported as “MTB detected” specimens by Abbott-RT were proceeded to Abbott-RIF/INH. A total of 3 MDR-TB, 1 RIF-mono resistantand6 INH-mono resistant specimens from the 53 MTB culture positive specimens were identified based on the phenotypic DST results of PHLC. Abbott-RIF/INH identified 3/3 (100%) MDR-TB, 1/1 (100%) mono-INH^R and 5/6 (83.3%) mono-INH^R specimens from the 10 phenotypic drug resistant specimens. The remaining 43 phenotypically RIF and INH susceptible isolates were all reported as WT by Abbott-RIF/INH. RIF^R and INH^Rdetected by Abbott-RIF/INH demonstrated (4/4)100% and (8/9)88.9% concordance by comparing with phenotypic DST respectively. In conclusion, the Abbott RealTime MTB Detection and RIF/INH Resistance Assay (Abbott-MDR) could fulfill the manufacturer’s claim on sensitivity and specificity, and demonstrated higher sensitivity than the in-house single-tube nested (STN) IS6110 real time duplex PCR assay for MTB detection in this evaluation. Therefore, the finding of the study suggested that the Abbott-MDR platform is a potential and suitable alternative for molecular detection of MTB and the genetic markers for RIF and INH resistance on respiratory specimens in clinical TB Laboratory.