The new finding doesn’t change that understanding: a single cough can expel more bacteria than a single breath. But if an infected person breathes 22,000 times a day while coughing up to 500 times, the cough makes up less than 7% of the total bacteria emitted by an infected patient, Dinkell said.
On a crowded bus, at school or at work, where people sit in confined spaces for hours, Mr Dinkel said: “Just breathing would contribute more to the spread of infectious aerosols than a cough.”
In what is called tidal breathing, inhalation causes tiny air sacs to open in the lungs, then exhalation carries bacteria from the lungs through the aerosol. Due to their small size, aerosols released by tidal breathing can stay afloat longer and travel farther than droplets released by coughing.
As with Covid, some TB patients transmit the disease to many people – and can release a lot of bacteria – while others infect a few people around them. But even if 90% of the bacteria expelled by an infected person were transmitted by aerosols, this route of transmission would not necessarily represent 90% of new cases, warned Dr Sylvia Chiang, who studies the disease at Brown University.
However, according to experts, the results suggest that doctors should not wait for TB patients to arrive at clinics with severe coughs and weight loss, and these symptoms are alarming.
“We just need to screen the whole population, like you would if you were testing a lot for Covid,” Dr Horsberg said.
The discovery is largely due to technology developed by Dr Robin Wood, Emeritus Professor of Medicine at the University of Cape Town in South Africa. The device can collect aerosols from infected people and identify the bacteria they contain.