Harnessing cough to detect TB
Tuberculosis (TB) spreads through an airborne route when an individual inhales aerosols (airborne particles <5µm in diameter) containing live Mycobacterium tuberculosis (Mtb) bacteria. Traditionally, TB has always been detected by checking for the presence of the bacteria in sputum of the afflicted person. However, this method cannot distinguish between live or dead Mtb and may not be an effective indicator for understanding the spread of the disease. We may also miss detecting patients when they are not able to produce sputum which is common especially in children. Recent studies have shown that aerosols released from TB patients during coughing are a better indicator for measuring the spread of the disease. To this effect, a study was conducted by Foundation for Medical Research to check the presence of Mtb derived molecules called RNA in cough aerosols retained on surgical face masks worn by patients. The detection of RNA indicates the presence of live bacteria.
Findings of the study show that RNA can be obtained from patients who have worn a mask for as low as 1 hour. M.tuberculosis specific genes could be detected in the RNA isolated from aerosols collected on patient’s mask using molecular approach (real-time PCR), which confirms the presence of viable Mtb. Further investigation showed that when the surgical mask is replaced by modified N95 masks carrying special membrane filters, the bacteria could be detected if worn for 5 minutes by the patient. This approach proved more effective than the use of surgical face mask as more amount of RNA could be obtained with a higher expression of Mtb specific genes and had more acceptability among the participating patients.
The study shows that aerosols collected on the mask worn by the patients can be used as a molecular diagnostic tool for detecting live Mtb bacterias. This sampling method would be very helpful in diagnosing TB in patients who have difficulty in producing sputum and in child cases. The ongoing study is funded by Tata Trusts through India Health Fund.
