Not just coughing, M. tuberculosis may be transmitted via simple breathing as well: Study

South Africa: A South African study reported that tidal breathing (TiBr) accounts for an estimated 93% of Mycobacterium tuberculosis (Mtb) produced over 24 hours in patients with active TB and along with inter-individual variability; it is a significant contributor to TB transmission.

The study was published in the American Journal of Respiratory and Critical Care Medicine. After a century of research, it is thus clear that transmission of airborne pathogens like M. tuberculosis does not always require a cough – all it takes is a simple breath.

For a long time, coughing has been considered the central mechanism of tuberculosis (TB) transmission. Recent evidence of cough-independent Mtb release implies the contribution of alternative mechanisms like simple tidal breathing. In Previous studies patients with TB were found to generate bioaerosols of the appropriate size for transmission (1-5 μm) during tidal breathing and at a higher rate than people without TB. But the presence of viable M. Tuberculosis in those aerosols and its comparison to those generated by coughing is uncertain.

Ryan Dinkele, University of Cape Town Institute of Infectious Disease and Molecular Medicine, South Africa conducted the study to compare the aerosolization of Mtb bacilli and total particulate matter from TB patients during three separate respiratory maneuvers: Tidal Breathing (TiBr), Forced Vital Capacity (FVC), and cough.

Researchers combined noninvasive bioaerosol capture technology with fluorescence microscopy to detect and count viable Mycobacterium tuberculosis in samples from 38 adults with untreated, Xpert-positive pulmonary TB with symptomatic TB. Bioaerosols were obtained before initiation of TB therapy and evaluated during forced vital capacity (FVC), coughing, and tidal breathing.

Key findings of the study,

• For all maneuvers, the proportions of particles detected across five size categories were similar with most particles falling between 0.5–5 μm.

• Although total particle counts were 4.8-fold greater in cough samples than in either TiBr or FVC, all three maneuvers returned similar rates of positivity for Mtb( 70% in cough samples, 66% in tidal volume samples, and 65% in FVC samples)

• No correlation was observed between total particle production and Mtb count. Instead, for total Mtb counts, the variability between individuals was greater than the variability between sampling maneuvers

• Finally, when modeled utilizing 24-hour breath and cough frequencies, our data indicate that TiBr might contribute >90% of the daily aerosolized Mtb among symptomatic TB patients.

The authors conclude that tidal breathing contributes most of the daily exhaled viable mycobacteria and thus could be a major contributor to transmission. Assuming the number of viable Mtb organisms released offers a reliable proxy of patient infectiousness, so focus should be on efforts to identify such patients and mitigate Mtb transmission. For active TB patients, a strategy of just "covering one's cough" should be promoted to slow transmission.

The study provides a compelling piece of evidence that tidal breathing may be an important – if not the major – mechanism of transmission for the airborne pathogen, the authors wrote.

References

1) 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)

2) 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)