Tuberculosis, like Covid, spreads through breathing, scientists report

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Tuberculosis, like Covid, spreads through breathing, scientists report

Following a centuries-old medical dogma, a team of South African researchers has found that breathing may be a bigger contributor to the spread of tuberculosis than cough, the signature symptom.

Researchers have estimated that up to 90 percent of TB bacteria released from an infected person can be carried in tiny droplets called aerosols, which are exhaled when a person takes a deep breath. The findings were presented Tuesday at a scientific conference held online.

The report echoes an important finding of the Covid pandemic: the coronavirus, too, spreads in aerosols, particularly in indoor spaces – a route of transmission that was widely underestimated since the pandemic unfolded.

TB is caused by a bacterium called Mycobacterium tuberculosis, which usually attacks the lungs. According to a report published last week by the World Health Organization, claiming more than 1.5 million lives last year, it is the world’s deadliest infectious disease after Covid-19 – the first increase in a decade.

As the Covid pandemic disrupted access to health care and supply chains around the world, 5.8 million people were diagnosed with TB in 2020. But the WHO estimates that around 10 million people were infected. Many may be unknowingly spreading the disease to others.

“Our model would suggest that, in fact, aerosol generation and TB generation may be independent of symptoms,” said Ryan Dinkley, a graduate student at the University of Cape Town who presented the results.

This finding helps explain why tightly packed indoor spaces, such as prisons, are often as breeding grounds for TB as they are for Covid. And research shows that some of the methods used to limit coronavirus transmission – masks, open windows or doors, and stay outside as much as possible – are important in reducing TB.

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“Those of us who are TB people look at COVID and say, ‘Wow, that’s a faster version of TB,'” said Dr. Robert Horsberg, an epidemiologist at Boston University who was not involved in the work.

Researchers previously believed that most TB transmission occurs when an infected person coughs, spraying droplets containing the bacteria into the air. Some bacteria are believed to be released when a person breathes in, but very little by coughing.

The new discovery doesn’t change that understanding: A cough can expel more bacteria than a single breath. But if an infected person breathes in 22,000 times daily while coughing 500 times, the cough accounts for 7 percent of the total bacteria excreted by an infected patient, Mr Dinkley said.

On a crowded bus or at school or work, where people sit in confined spaces for hours, “just inhaling will contribute more infectious aerosols than coughing,” Mr Dinkley said.

In so-called tidal breathing, inhalation opens up small air sacs in the lungs, and then exhalation moves bacteria out of the lungs via an aerosol. Because of their small size, aerosols released by tidal breathing can remain in the air for longer and travel farther than droplets released by coughing.

As is the case with Covid, some TB patients spread the disease to many people – and can release a lot of bacteria – while others infect a few people around them. But even if 90 percent of the bacteria exhaled by an infected person is carried in aerosols, this route of transmission will not be responsible for 90 percent of new cases, said Dr. Sylvia S. Chiang warned.

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Still, experts said, the finding suggests that physicians should not wait to come to clinics for TB patients with severe cough and weight loss, which are its symptoms.

“We need to test the entire population, just like you would if you’re looking for a lot of covids,” said Dr. Horsberg.

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

Little has changed in the diagnosis and treatment of TB over the decades. “It was time to start using modern, state-of-the-art technology to tackle a chronic disease,” said Dr. Wood. He said that with some modifications, this system can also be used to study other diseases including Kovid.

TB has been around for millennia, and its cause has been known for nearly 150 years.

“And yet, we are still discovering new things about such a fundamental part of its biology,” said Mr. Dinkley. “It’s humbling to realize that we need to be very careful when it comes to dogma in a field.”

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