Abstract
Timely diagnosis of drug-resistant tuberculosis (DR-TB) is beneficial for case treatment and management. We implemented an algorithm to improve molecular diagnostic utilization to intensify DR-TB case findings. The GeneXpert MTB/RIF (Xpert) test was used for initial diagnosis. Samples with Mycobacterium tuberculosis complex (MTBC)-positive and rifampicin resistance (RR) results were subsequently and simultaneously tested using the GenoType MTBDRplus (DRplus) and MTBDRsl (DRsl) tests. This prospective cohort study enrolled 2957 high-risk DR-TB cases. We tested sputum specimens using conventional mycobacteriological and molecular tests. Gene sequencing was performed to resolve discordant results. According to the Xpert test, 33.6% of specimens were MTBC-positive and 5.1% were RR. RR specimens were further analyzed in the DRplus and DRsl tests. We identified 1 extensively drug-resistant (XDR), 8 pre-XDR, 18 simple multidrug-resistant (MDR), 22 mono-RR, and 2 RR cases with concurrent second-line injection DR-TB. Of these, 25 (49%) were relapses, 13 (25.5%) were treatment failures, 10 (19.6%) were from MDR-TB high-incidence areas/countries, 1 was from MDR-TB contact and 2 were unknown. Among culture-positive TB cases, the sensitivities, specificities, and positive predictive values (PPVs) of the Xpert test and RR cases were 73.6% and 100.0%, 85.7% and 98.6%, and 73.5% and 80.0%, respectively. Gene sequencing of discordant results revealed 7 disputed rpoB mutations and 2 silent mutations for RIF, 1 ahpC mutation for isoniazid and 1 gyrA mutation for fluoroquinolone. The algorithm effectively identified approximately 23% of annual MDR-/XDR-TB and 37.5% of RR-TB cases that were enrolled in our DR-TB treatment and management program within 3 days.
Highlights
Tuberculosis (TB) is a major public health concern worldwide and a notable communicable disease in Taiwan
The Xpert test is a semi-nested real-time polymerase chain reaction (PCR)-based assay, which uses three primers to amplify the Mycobacterium tuberculosis complex (MTBC)-specific sequence of the rpoB gene and five fluorescent wild-type probes to screen the 81-bp rifampicin resistance determining region (RRDR)
Of the 2957 specimens tested, we identified 958 (32.4%) specimens that were MTBC culture-positive, 1532 (51.8%) that were culture-negative for mycobacteria, 240 (8.1%) that were nontuberculous mycobacteria (NTM)
Summary
Tuberculosis (TB) is a major public health concern worldwide and a notable communicable disease in Taiwan. The Xpert test is a semi-nested real-time polymerase chain reaction (PCR)-based assay, which uses three primers to amplify the MTBC-specific sequence of the rpoB gene and five fluorescent wild-type probes to screen the 81-bp (codon 507–533) rifampicin resistance determining region (RRDR). The DRplus test is a commercially available line-probe assay (LPA) that identifies MTBC and resistance to RIF and INH, including mutations in the 81-bp hotspot region of the rpoB and the inhA promoter region at codon 315 of the katG gene This test is based on DNASTRIP technology, comprising DNA extraction, multiplex polymerase chain reaction (PCR) with biotinylated primers, and reverse hybridization, with a turnaround time of less than 8 hours [8]. To further improve the utilization of molecular diagnostics for case management, we implemented and evaluated the diagnostic performance of an algorithm with the Xpert test and 2 LPAs to expand and to streamline the screening of both smear-positive and smear-negative high-risk, DR-TB populations
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