# Diagnostic accuracy of the BD MAX MDR-TB assay on sputum and tongue swabs for Mycobacterium tuberculosis complex detection in adults under investigation for TB in South Africa

## TL;DR

This study evaluates the BD MAX MDR-TB assay's accuracy in detecting TB and drug resistance in South Africa using sputum and tongue swabs.

## Contribution

The study provides new clinical performance data for the BD MAX MDR-TB assay on sputum and tongue swabs in a high HIV-prevalence TB setting.

## Key findings

- The MAX MDR-TB assay showed 88.7% sensitivity and 98.2% specificity for TB detection in sputum compared to culture.
- Tongue swabs with diluted STR buffer showed 66% diagnostic accuracy for TB detection.
- The assay had two false RIF-resistant results and missed INH resistance in two cases.

## Abstract

Despite the availability of molecular diagnostics, only 48% of newly diagnosed tuberculosis (TB) cases were confirmed using nucleic acid amplification tests in 2023. The MAX Multi Drug Resistant Tuberculosis (MAX MDR-TB) assay detects Mycobacterium tuberculosis complex (MTBC) and resistance to rifampicin (RIF) and isoniazid (INH), but data on clinical performance are limited. This study assessed the assay’s performance on sputum and tongue swabs (TSs). The assay was evaluated for MTBC detection and RIF and INH resistance profiling on sputum using liquid culture as the reference and Xpert MTB/RIF Ultra (Ultra) as a comparator. Diagnostic accuracy for MTBC detection on TS was also assessed. Among 335 participants (56% HIV prevalence), MAX MDR-TB on raw sputum showed an overall sensitivity and specificity of 88.7% (95% confidence interval [CI]: 78.1–95.3) and 98.2% (95% CI: 95.8–99.4) compared with culture and strong agreement with Ultra (Cohen’s kappa = 0.853). A total of 15/55 (27%) sputum samples were classified as “MTB low POS.” Two false RIF-resistant results were observed. INH resistance was missed in two cases. Although specimen numbers were small, TS demonstrated better diagnostic accuracy when using a diluted sample treatment reagent (STR) (66%) buffer. Although the MAX MDR-TB assay demonstrated good agreement with Ultra, Ultra identified more TB cases. Preliminary findings suggest that TS, particularly with a diluted STR buffer, may be a feasible specimen type, but larger studies are required. The high frequency of MTB low POS results highlights the importance of technology assessment by TB programs prior to implementation to minimize repeat testing and enhance diagnostic reliability.

This study evaluates the accuracy of the BD MAXTM MDR-TB assay in detecting Mycobacterium tuberculosis complex using sputum and tongue swabs from individuals being assessed for tuberculosis (TB) in South Africa. Rapid and reliable TB diagnosis is crucial for early treatment and preventing transmission. The MAX Multi Drug Resistant Tuberculosis (MAX MDR-TB) assay is a fully automated molecular test that can simultaneously detect TB and drug resistance, offering a potentially faster and more efficient alternative for TB diagnosis. By assessing its performance on different specimen types, this study provides valuable insights into its reliability in clinical settings. Although the MAX MDR-TB assay demonstrated strong agreement with the Xpert MTB/RIF Ultra assay, it identified fewer TB cases. Tongue swabs were also shown to be a feasible specimen type for testing. This research contributes to global TB control efforts by evaluating advanced diagnostics that could streamline testing, reduce delays, and ultimately improve patient outcomes.