Loading...
Although never confirmed, coughing has long been considered the central mechanism of tuberculosis (TB) transmission. However, evidence indicates that cough-independent mechanisms are also important. One such mechanism is the generation of bioaerosols during tidal breathing. Researchers in South Africa combined noninvasive bioaerosol capture technology with fluorescence microscopy to detect and count viable Mycobacterium tuberculosis in samples from 38 adults with symptomatic TB. Bioaerosols were obtained prior to initiation of TB therapy and evaluated during forced vital capacity (FVC), coughing, and tidal breathing.
In assessments of 15 FVC and 15 cough maneuvers compared with 5 minutes of tidal breathing, viable M. tuberculosis was found in 70% of cough samples, 66% of tidal volume samples, and 65% of FVC samples. Overall, the average number of viable M. tuberculosis produced by tidal breathing was 2.6-fold fewer than FVC and 3.2-fold fewer than cough. However, comparing the estimated 22,047 tidal breaths daily to an estimated 466 coughs daily, tidal volume was found to contribute 93% of the total number of viable M. tuberculosis released, compared with 7% for cough over a 24-hour period.
Dinkele R et al. Aerosolization of Mycobacterium tuberculosis by tidal breathing. Am J Respir Crit Care Med 2022 May 18; [e-pub]. (https://doi.org/10.1164/rccm.202110-2378OC)
Dowdy DW.Coughing is not required to transmit Mycobacterium tuberculosis: Another nail in the coffin. Am J Respir Crit Care Med 2022 May 25; [e-pub]. (https://doi.org/10.1164/rccm.202204-0645ED)
Comment
Although viability was based on fluorescence and not culture, these results suggest that tidal breathing contributes most of the daily exhaled viable mycobacteria and thus could be a major contributor to transmission. If true, this finding should focus our efforts on identifying those who produce viable bioaerosols and mitigating their transmission.