Evaluation of the BD MAX™ MDR-TB assay in a real-world setting for the diagnosis of pulmonary and extra-pulmonary TB

Tuberculosis in London occurs at a rate of 19 cases per 100,000 population, with a significant proportion diagnosed as extra-pulmonary infection. At Barts Health NHS Trust, our TB rates are much higher than the London average and approximately 60% cases are extra-pulmonary in nature. We evaluated the BD MAX™ MDR-TB assay as a molecular tool for rapid diagnosis of TB. One hundred twenty-eight specimens, encompassing pulmonary (70) and extra-pulmonary (58) infection, were tested using the BD MAX™ MDR-TB assay and compared with smear and liquid culture results, to determine PCR performance. The BD MAX™ MDR-TB assay was also compared with the Xpert MTB/RIF assay, where applicable. TB was successfully detected in 50/66 Mycobacterium tuberculosis culture positive specimens, with additional detections in 2 of the culture negative specimens. The BD MAX™ MDR-TB assay demonstrated higher sensitivity with the pulmonary samples (92%) compared with the extra-pulmonary samples (52%), although the performance with fluids and biopsies demonstrated greater potential than the remaining extra-pulmonary samples. Rifampicin and/or isoniazid resistance was successfully detected by the BD MAX™ in 2/3 samples, where WGS susceptibility results were available. The BD MAX™ MDR-TB assay was comparable with the performance of the Xpert MTB/RIF assay. TB can successfully be diagnosed, in both pulmonary and extra-pulmonary samples, using the BD MAX™ MDR-TB assay.