Mycobacteria cause various illnesses. Mycobacterium tuberculosis, the main representative of this genus, is the causative agent of tuberculosis, which killed around 1.5 million people worldwide in 2014. Nontuberculous mycobacteria can trigger pulmonary infections, lymph node infections and skin diseases in patients with compromised immune systems. On account of more and more people with chronic lung diseases and the success of transplants, these difficult-to-treat infections have been on the rise continuously in recent decades.
What used to take several weeks is now possible in two days: thanks to new molecular-based methods, mycobacterial pathogens that cause pulmonary infections or tuberculosis can now be detected much more quickly. Time-consuming bacteria cultures no longer need to be taken from the patient samples, meaning that a suitable therapy can be started quickly.
For their study, the researchers developed a diagnostic algorithm to detect mycobacteria directly from the patient sample using genetic analysis. With this ultra-fast molecular detection method, the patient samples were examined continuously over three years and compared with the results from the bacteria cultures for more than 3,000 patients. The new molecular-based methods were found to be just as accurate as the lengthy culture-based techniques used to date.
The molecular-based detection and culture gave concordant results for 97.7% of the specimens. NTM PCR-based detection and culture gave concordant results for 97.0% of the specimens. Defining specimens on the basis of combined laboratory data as true positives or negatives with discrepant results resolved by clinical chart reviews, authors calculated sensitivity, specificity, PPV and NPV for PCR-based MTB detection as 84.7%, 100%, 100%, and 98.7%; the corresponding values for culture-based MTB detection were 86.3%, 100%, 100%, and 98.8%. PCR-based detection of NTM had a sensitivity of 84.7% compared to 78.0% of that of culture-based NTM detection.
In addition, the molecular analysis makes it possible for the first time to also detect the nontuberculous mycobacteria directly from the patient sample within just a few hours. This means that suitable therapeutic measures can be initiated much more quickly. By contrast, if the patient has a tuberculosis infection, a further molecular assay is carried out to test susceptibility to the main tuberculosis drugs "rifampicin" and "isoniazid". "This also showed that the molecular-based method reliably predicts the culture-based resistance results. It is possible to obtain certainty much sooner of whether the therapy with standard medicines chosen is likely to be successful", explains the author.
Faster detection of pathogens in the lungs
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