The new finding does not change that understanding: A single cough can expel more bacteria than a single breath. But if an infected person breathes 22,000 times per day while coughing up to 500 times, then coughing accounts for as little as 7 percent of the total bacteria emitted by an infected patient, Mr. Dinkele said.
On a crowded bus or at school or work, where people sit in confined spaces for hours, “just simply breathing would contribute more infectious aerosols than coughing would,” Mr. Dinkele said.
In so-called tidal breathing, inhalation opens up tiny air sacs in the lungs, and then exhalation carries the bacteria from the lungs via aerosols. Because of their smaller size, aerosols released by tidal breathing can stay afloat in the air for longer and travel further than droplets emitted by a cough.
As with Covid, some TB patients spread the disease to many people — and may release a lot of bacteria — while others infect few people around them. But even if 90 percent of the bacteria expelled by an infected person were carried in aerosols, this route of transmission wouldn’t necessarily account for 90 percent of new cases, cautioned Dr. Silvia S. Chiang, who studies the disease at Brown University.
Still, experts said, the finding does suggest that physicians shouldn’t wait for TB patients to arrive at clinics with a severe cough and weight loss, the telltale symptoms.
“We just need to screen the entire population, just like you would do if you’re looking for a lot of Covid,” Dr. Horsburgh said.
The discovery came about in large part because of technology developed by Dr. Robin Wood, an emeritus professor of medicine at the University of Cape Town in South Africa. The apparatus can collect aerosols from infected people and identify bacteria within them.