Correction to Letter to the Editor "Prevalence and causes of rifampicin-resistance genotypic/phenotypic discrepancy detected on Xpert MTB/RIF in Singapore" [Ann Acad Med Singap 2024;12:766]

The Xpert Mycobacterium tuberculosis/rifampicin (MTB/RIF) (Cepheid, Sunnyvale, CA, US) has been pivotal in tuberculosis (TB) diagnostics, enabling the rapid detection of both TB and RIF resistance. Xpert, a nucleic acid amplification test (NAAT), is recommended by both the World Health Organization (WHO)1 and Singapore’s clinical management guidelines2 as a frontline diagnostic tool for TB and RIF resistance. With a high specificity rate (98%) in detecting RIF resistance, Xpert has a positive predictive value (PPV) exceeding 90% in settings where the prevalence of RIF resistance is above 15%.3 However, in Singapore, a country with medium-incidence of TB and low prevalence of RIF resistance (<1% among individuals born in Singapore), 4 the PPV of detecting RIF resistance via Xpert is substantially lower.3 Phenotypic-genotypic discrepant RIF resistance have been reported to result from technical errors, false-positive results in paucibacillary samples,5 silent mutations6 or disputed mutations where minimal inhibitory concentrations (MICs) fall below critical concentrations in phenotypic drug susceptibility testing (pDST) systems.7 We conducted a quality assessment of sputum samples which tested positive for TB and RIF resistance using point-of-care Xpert at the Singapore National Tuberculosis Care Centre (NTBCC) to determine the prevalence and causes of false-positive RIF resistance.