Like Covid-19, tuberculosis spreads through aerosols: Report

NEW YORK • Upending centuries of medical dogma, a team of South African researchers has found that breathing may be a bigger contributor to spreading tuberculosis (TB) than coughing, the signature symptom.

As much as 90 per cent of TB bacteria released from an infected person may be carried in tiny droplets, called aerosols, that are expelled when a person exhales deeply, the researchers estimated.

The findings were presented on Tuesday at a scientific conference held online. The report echoes an important finding of the Covid-19 pandemic: The coronavirus, too, spreads in aerosols carried aloft, particularly in indoor spaces.

TB is caused by a bacterium called Mycobacterium tuberculosis, which usually attacks the lungs. It is the world's deadliest infectious disease after Covid-19, claiming more than 1.5 million lives last year - the first increase in a decade, according to a report published by the World Health Organisation (WHO) last week.

As the pandemic disrupted access to healthcare and supply chains around the globe, 5.8 million people were diagnosed with TB last year. But the WHO estimates about 10 million people were infected.

"Our model would suggest that, actually, aerosol generation and TB generation can happen independent of symptoms," said Mr Ryan Dinkele, a graduate student at the University of Cape Town, who presented the results.

The finding helps explain why tightly packed indoor spaces often are breeding grounds for TB, as for Covid-19. The research suggests that some methods used to limit coronavirus transmission - masks, open windows or doors, and being outdoors as much as possible - are important in curtailing TB.

"Those of us who are TB people look at Covid-19 and say, 'Wow, it's just a sped-up version of TB'," said Dr Robert Horsburgh, an epidemiologist at Boston University who was not involved in the work.

Researchers previously believed that most TB transmission occurred when an infected person coughed, spraying droplets containing bacteria onto others. Much less bacteria was thought to be released when a person breathed.

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 a day while coughing up to 500 times, then coughing accounts for as little as 7 per cent of the total bacteria emitted, Mr Dinkele said.

When people sit in confined spaces for hours, "just simply breathing would contribute more infectious aerosols than coughing would", he said.

5.8 million Number of people diagnosed with tuberculosis last year.

10 million Number of people the World Health Organisation estimates were infected with tuberculosis last year.

Experts said the finding suggests physicians should not wait for TB patients to arrive at clinics with the telltale symptoms of a severe cough and weight loss. "We need to screen the entire population, just like you would do if you're looking for a lot of Covid-19," Dr Horsburgh said.

The discovery was due in large part to technology developed by Dr Robin Wood, an emeritus professor of medicine at the University of Cape Town. The apparatus can collect aerosols from infected people and identify bacteria within them.

NYTIMES