Long-forgotten technique of detecting TB revived
Washington: Researchers have breathed new life into a forgotten technique and so succeeded in detecting resistant tuberculosis in circumstances where so far this was hardly feasible.
Tuberculosis bacilli that have become resistant against our major antibiotics are a serious threat to world health.
If we do not take efficient and fast action, ‘multiresistant tuberculosis’ may become a worldwide epidemic, wiping out all medical achievements of the last decades.
Checking smears under the microscope still is the recommended technique for TB screening, but it cannot differentiate between living and dead bacilli.
With high-tech PCR technology one can immediately ascertain if the bacillus is from a resistant strain, but in practice and certainly in resource-limited countries this is unfeasible.
It also is impossible to cultivate every sample and then bombard it with every possible antibiotic to survey which ones still work for that individual patient.
Armand Van Deun and colleagues therefore gave a new application to a forgotten technique: vital staining with fluorescein diacetate (FDA).
It only stains living TB bacilli, so one immediately sees those bacilli escaping treatment. The scientists improved the detection of the luminous bacilli by replacing the classical fluorescence microscope with its LED counterpart.
Together with colleagues in Bangladesh they tested the approach in the field for four years. This was made possible by a grant from the Damien Foundation – another possible sponsor had fobbed them off because their technique was too unknown.
But their approach works, also in a poor country. If after treatment the FDA-test was negative, in 95 percent of cases more elaborate tests didn’t find active bacilli in the patient``s sputum either. And if the test was positive, you could bet your boots that you had found a resistant bacillus.
This simple test allows, also in resource-limited labs, to detect a high number of resistant TB bacilli that otherwise would have been discovered too late or not at all.
The scientists reported that three times more patients could directly switch to the correct second-line treatment without losing time on a regimen ineffective against their resistant bacilli.
On top of that, the technique can cut in half the number of cases where doctors start a retreatment ‘just to stay on the safe side’, because it ascertains that the bacilli detected by the classical microscopy in fact are dead ones, which do not require further treatment.
The study has been published in the International Journal of Tuberculosis and Lung Disease.