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.

Date of Award	16 Jun 2023
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Wilber Sabiiti (Supervisor) & Stephen Henry Gillespie (Supervisor)