Evaluation of the tuberculosis-molecular bacterial load assay for tuberculosis diagnosis and monitoring response to standard anti-tuberculosis therapy

Abstract

Tuberculosis (TB) is a difficult disease to treat, requiring a minimum of six months on a combination of four antibiotics. This thesis reports the first systematic evaluation of the St Andrews' developed RNA-based tuberculosis-Molecular Bacterial Load Assay (TB-MBLA) for its accuracy to diagnose tuberculosis and measure treatment response in comparison to current standard-of-care tests. Presumptive TB patients were enrolled in Uganda and assessed for TB using TB-MBLA versus Xpert MTB/RIF Ultra (Xpert-Ultra) and stained smear fluorescent microscopy (SSM-FM) using sputum MGIT culture as the gold standard and reference test. Out of the 210 presumptive cases, 129 (61.4%) participants tested TB positive on the Xpert-Ultra in the sputum cohort and they were enrolled into the treatment arm and consequently monitored for six months. At baseline, 6/210 (2.9%) sputum MGIT culture results were indeterminate due to contamination, and they were excluded from the calculation of the sensitivity, specificity, and predictive values. Sensitivity for TB-MBLA and Xpert-Ultra (95%CI) was 99%(95-100) which was higher compared to 76%(65-83) for SSM-FM. TB-MBLA specificity at 90%(83-96) was higher than the 76%(68-86) for Xpert-Ultra but less than 98%(93-100) for SSM-FM. In the treatment follow-up arm, TB positivity rates reduced for all tests. TB-MBLA positivity reduction was consistent with that of the MGIT culture but different from that of Xpert-Ultra which occurred remarkably slower. Consequently, 31 participants were still Xpert-Ultra positive at the end treatment course. Three-month post treatment follow-up of the 31 Xpert-Ultra positive cases revealed no TB both clinically and on TB-MBLA and MGIT tests. In the stool cohort, TB-MBLA detected TB in 57/100 participants including 49 who were confirmed positive for pTB on sputum MGIT culture. Fifty-seven percent (57%) of the indeterminate stool culture were positive on TB-MBLA. The findings prove that TB-MBLA's potential utility as both a diagnostic and treatment monitoring tool of TB in research and routine healthcare.