Is Drug-Resistant TB Hiding in Plain Sight? How Rapid Testing Can Help
"A new study from Nigeria highlights the importance of quick and accurate testing for multi-drug resistant tuberculosis (MDR-TB) to improve patient outcomes and curb transmission."
Tuberculosis (TB) continues to be a significant public health challenge, particularly in developing nations. The situation is made worse by the increasing number of Mycobacterium tuberculosis strains that have become resistant to first-line anti-TB drugs. This resistance, known as multi-drug resistant TB (MDR-TB), demands urgent and effective diagnostic and treatment strategies.
While microscopy remains a widely accessible diagnostic tool, it falls short in detecting drug resistance. Culture methods, though considered the gold standard for diagnosis and drug resistance testing, are often hampered by prolonged turnaround times, high costs, and limited availability. These limitations underscore the need for innovative diagnostic approaches.
The Gene Xpert Mycobacterium tuberculosis/Rifampicin (MTB/Rif) assay emerges as a promising solution. This rapid diagnostic test allows for quick identification of tuberculosis and simultaneous detection of rifampicin resistance, a key indicator of MDR-TB. A recent study conducted at Nnamdi Azikiwe University Teaching Hospital in Nigeria evaluated the performance of the XpertMTB/Rif assay in detecting MTB and drug-resistant TB within one year of its installation.
The Continuing Burden of Drug-Resistant TB
The World Health Organization estimated that multidrug-resistant or rifampicin-resistant TB caused 150,000 deaths globally in 2024, with a 95% uncertainty interval of 93,000 to 210,000. A 2025 study reported an overall MDR-TB prevalence of 18.8% among its 250 participants, rising to 40.0% among previously treated patients. In the United States, drug resistance remained uncommon in 2024, with 115 MDR-TB cases among 7,475 TB cases.
Culture and Molecular Drug-Susceptibility Testing
Successful MDR-TB diagnosis and treatment depend on rapid, precise drug-sensitivity testing to guide selection of effective medicines. Drug-resistance testing, also called antimicrobial susceptibility testing, is mandatory for Mycobacterium tuberculosis when standard therapy fails. Canadian tuberculosis standards describe two diagnostic routes: phenotypic testing through culture and molecular or genomic methods, with phenotypic drug-susceptibility testing remaining part of the diagnostic framework.
From Koch to Streptomycin
The infectious origin of TB was conjectured by English physician Benjamin Marten in 1720. On March 24, 1882, Dr. Robert Koch announced the discovery of Mycobacterium tuberculosis, the germ that causes TB. A later milestone came in 1943, when streptomycin purified from Streptomyces griseus showed strong inhibition of M. tuberculosis with relatively low toxicity in test animals.
Unveiling the Gene Xpert: A Game-Changer in TB Detection
The Gene Xpert machine represents a significant advancement in TB diagnostics due to its speed, sensitivity, and specificity. This cartridge-based, automated test can detect Mycobacterium tuberculosis and rifampicin resistance in under 2 hours. The system uses three specific primers and five unique molecular probes to ensure a high degree of accuracy.
- Speed and Accuracy: The Xpert MTB/RIF assay provides results in about 2 hours, enabling quicker diagnosis and treatment decisions.
- Simultaneous Detection: It detects both the presence of TB bacteria and resistance to rifampicin, a key drug in TB treatment.
- Ease of Use: The system requires minimal technical expertise and has a simple, hands-on operation.
- Reduced Contamination Risk: The use of sealed and disposable cartridges minimizes the risk of cross-contamination.
Research on Prevention, Treatment, and Case Finding
A 2025 narrative review examined available drug regimens for treating people infected with MDR-TB strains. Earlier systematic-review work updated the evidence on MDR-TB treatment by searching for studies reporting treatment outcomes. A 2024 scoping review of drug-resistant TB case-finding strategies found that more than 60% of the identified studies described DR-TB case finding.
Where Current Testing Can Fail
Reviews of TB diagnostics identify major limitations in the current test repertoire, including the time required to obtain or generate results. A 2025 review of the MTB/RIF assay warns that false-positive and false-negative results for M. tuberculosis and rifampin resistance can lead to incorrect treatment, including treatment overuse. In low-resource settings, samples may be sent to distant laboratories, while many countries reserve culture for treatment failure or patients already considered drug-resistant.
Testing Concordance and Treatment Duration
A 2022 evaluation of three alternative cost-effective culture media reported excellent concordance with the reference test for susceptibility testing of MDR and PZA. The study described the concordance as 1, indicating agreement with its reference method. Separately, MedicineNet reports that both MDR-TB and XDR-TB generally take substantially longer to treat than ordinary TB infection.
A Call to Action: Expanding Access to Rapid TB Diagnostics
The study underscores the importance of rapid and accurate TB diagnostics, particularly in regions with a high burden of drug-resistant TB. The Xpert MTB/RIF assay offers a valuable tool for improving patient care and reducing TB transmission.
The Role of Rapid Molecular Assays
The European Reference Laboratory Network for TB states that rapid molecular assays have diagnostic value for identifying TB and detecting drug resistance, including MDR-TB and XDR-TB. The BD MAX MDR-TB molecular test has been reported as an effective rapid tool, particularly for detecting rifampicin resistance. However, the 2025 evaluation also reported that the test may not detect every relevant resistance pattern.
Forecasts and Research Innovation
A 2025 forecast study projected that the age-standardized incidence rate of MDR-TB would decrease from 5.37 in 2022 to 4.72 in 2030. The reported 2030 estimate had a 95% confidence interval of 2.44 to 6.99. The World Health Organization also reports that advances in TB research are transforming treatment options for people affected by drug-resistant forms of the disease, drawing on evidence from two clinical studies.
Diagnosis Gaps and Resistance Spectrum
MDR-TB is characterized by resistance to two of the most effective anti-TB drugs. Vital Strategies reports that only 32% of people with rifampicin-resistant or MDR-TB are diagnosed globally. Drug-resistant TB also includes a broader spectrum that encompasses extensively drug-resistant TB and, more recently, totally drug-resistant TB.
Earlier Detection and Patient Impact
A survivor story from India highlights the personal impact of MDR-TB and reports that molecular testing can detect MDR-TB at an earlier stage. The Treatment Action Group describes a rapid test that can detect TB and rifampicin resistance, a proxy for MDR-TB, in less than two hours from a sample. In India, the IPAQT initiative transformed the private-sector market for validated TB testing and documented effects on patients and partnering laboratories.
The WHO estimates that Nigeria ranks among the countries with the highest MDR-TB burden. Despite this, access to MDR-TB diagnostic facilities remains limited. To effectively combat TB, it's crucial to strengthen health systems and expand diagnostic capacity.
Making the Gene Xpert machine available in more centers would ensure rapid diagnosis of tuberculosis and rifampicin resistance, ultimately curbing the prevalence of MDR-TB. Increased investment in TB diagnostics is essential to achieve global TB control and improve public health outcomes.