Early experience with Xpert MTB/RIF Ultra point-of-care testing at the Singapore Tuberculosis Control Unit

The Tuberculosis Control Unit manages 80% of the national caseload:half arise from high TB and multi-drug resistant TB burden countries. Prior experience with Xpert MTB/RIF point-of-care testing since 2018 showed high sensitivity (73%) and specificity (97.7%) for TB detection. We report our early experience with Xpert MTB/RIF Ultra (Xpert Ultra) which replaced the Xpert MTB/RiF in May 2023. Xpert Ultra was performed on 1 ml of sputum. Remaining sample was sent for liquefaction, centrifugation and acid-fast bacilli (AFB) smear.AFB culture and phenotypic drug susceptibility testing (pDST) was performed on sputum pellets. From 4th May to 30th November 2023,3438 sputum samples were processed using Xpert Ultra:3435 underwent AFB culture. Xpert Ultra was positive for in 351(10.2%)samples: majority were low(37%), followed by trace(22.8%),very low(18%),high(11.7%) and medium(10.5%) load. Overall sensitivity and specificity of Xpert Ultra was 87.4% and 96.2% respectively;98.9% and 83.3% in smear-positive specimens, and 81.7% and 96.4% in smear-negative specimens. Specificity increased to 97.9% while sensitivity remained (86.1%) when trace samples were excluded. Indeterminate rpoB mutation was reported in 85(24.2%)samples:80(94.1%) in trace load. In the remaining 5,4 were Rifampicin(RIF) sensitive (1 high, 1 medium, 2 very low load)and 1 was resistant on pDST. Three samples had rpoB mutation on Xpert Ultra:2 were RIF resistant on pDST while 1 was culture negative. No pDST RIF resistance was missed by Xpert Ultra. Xpert Ultra had higher sensitivity and lower specificity for TB detection than Xpert MTB/RIF. Specificity improved with exclusion of trace samples. Xpert Ultra is useful in our setting.