Ordinary breathing, not coughing, behind most TB transmission, say UCT researchers

Researchers from the University of Cape Town (UCT) have cast doubt on the long-held belief that coughing is the main means of spreading tuberculosis (TB), presenting new research at international conference that found regular breathing may be a far bigger contributor.

The results suggest that the current approach to TB control, which relies on sick people seeking care, is potentially missing large numbers of asymptomatic patients.

Their research comes as TB programmes around the world struggle to deal with the disruption caused by the coronavirus pandemic. The number of new cases diagnosed fell for the first time in a decade in 2020, to 5.8 million, with about 4.1-million cases going undetected, according to the World Health Organisation (WHO). In 2020 about 1.5-million people died from TB, making it the second deadliest disease after Covid-19.  

The UCT scientists used a specially constructed chamber to study the relative contribution of coughing, deep breathing and regular, or “tidal”, breathing to the expulsion of tiny aerosols containing Mycobacterium tuberculosis, the bacteria that causes TB. They found tidal breathing contributed 90% of the aerosols expelled by an infected person, challenging the belief that coughing produced most of these droplets.

“Our research found that what matters most is the event frequency, as opposed to the event itself,” said the study’s lead author, UCT PhD student Ryan Dinkele. The findings suggest the current approach to TB control, which relies on testing and treating people who feel sick enough to seek care, may not be sufficient, he said in a virtual press conference hosted by the 52nd Union World Conference on Lung Health.

Union president Guy Marks said the study had important implications, suggesting far more effort needed to go into diagnosing patients who were not coughing. Greater attention should be paid, too, to reducing the risk of airborne transmission. “As we have learnt with Covid-19, we need to consider how to control [airborne transmission] more effectively, which may involve masks, ventilation, and methods of keeping the air safe,” he said.

Marks said the “shocking and dangerous” inequity in access to Covid-19 should come as no surprise, given the uneven access to TB services around the world.

“If we spent a fraction of the resources [spent on Covid-19], we would have stopped TB in its tracks many years ago. The failure to deliver Covid-19 vaccines to low- and middle-income countries, and the failure to end TB in low- and middle-income countries are two sides of the same coin. Essentially they represent a devaluation of life in poor countries,” he said.

“The devastating mortality numbers from the WHO global TB report indicate TB will soon return to the biggest killer [among] infectious diseases. This is a preventable tragedy,” he said.

kahnt@businesslive.co.za