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Face Masks Don’t Cause Legionnaires’ Disease

Quick Take

A viral social media post is spreading the falsehood that wearing a face mask to slow the spread of COVID-19 could cause Legionnaires’ disease. But Legionnaires’ disease is caused by bacteria that festers mostly in warm, standing water, not in human saliva.

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The latest falsehood to cast doubt on the safety of face masks makes the bogus assertion that wearing one can cause Legionnaires’ disease. It can’t.

As we’ve written before, the Centers for Disease Control and Prevention recommends wearing a face covering to help slow the spread of the novel coronavirus. But the issue has become politicized and misinformation about masks is now common online. We’ve already addressed several other related claims.

The latest example claims: “Mask wearers beware… ⚠️ A caller to a radio talk show recently shared that his wife was hospitalized and told she had COVID and only a couple of days left to live. A doctor friend suggested she be tested for legionnaires disease because she wore the same mask every day all day long. Turns out it WAS legionnaires disease from the moisture and bacteria in her mask. She was given antibiotics and within two days was better. WHAT IF these ‘spikes’ in COVID are really something else due to mask wearing??”

We don’t know where this claim originated, but the first instance of it that we could find on Facebook was on a page for “Setting The Record Straight with Ronald Dwyer,” which described itself as a “Media/News Company.” Dwyer did not respond to a call seeking comment and our message sent to the Facebook page administrator went unanswered.

The primary claim made in the post, which has been copied and shared widely on Facebook and Twitter, is false. People cannot get Legionnaires’ disease from wearing a face mask, Dr. Janet Stout told FactCheck.org in a phone interview. Stout is the president and director of the Special Pathogens Laboratory in Pittsburgh, Pennsylvania, and has studied that disease for decades.

Legionnaires’ disease was first documented during an American Legion convention in Philadelphia in 1976, which gave the disease its name. It is caused by bacteria, while COVID-19 is caused by a virus. Bacteria are single-cell organisms that can live in various environments, while viruses, which are smaller than bacteria, need a living host in order to multiply. We’ve written before about that distinction.

Referring to the bacteria, Stout explained, “Legionella is not spread from one person to another.” Rather, it is spread mostly by breathing in mist from infected water sources, which are usually warm and stagnant and commonly include hot tubs or air-conditioning cooling towers, according to the CDC. The disease can also be caused by drinking infected water if some of the water enters the lungs.

The bacteria would not be present in saliva, Stout said, so there would be no way for moisture from a person’s own spit to cause Legionnaires’ disease.

The two diseases — Legionnaires’ and  COVID-19 — do share some symptoms, though. Stout highlighted that they both cause high fevers, a cough, and sometimes diarrhea. They also endanger the same high-risk patients — the elderly and those with underlying diseases. So, she said, it’s conceivable that doctors who have a heightened awareness of COVID-19 right now might initially mistake Legionnaires’ disease for COVID-19. But the two diseases have different tests.

The COVID Tracking Project reports that, since Jan. 22, there have been more than 5 million positive COVID-19 tests in the U.S.

For Legionnaires’ disease, the most recent data available from the CDC is from 2018, when there was a total of 10,000 reported cases in the U.S. That number, however, is probably lower than the actual amount of cases since the disease is likely underdiagnosed, according to the CDC.

The bottom line with regard to mask wearing and Legionnaires’ disease, though, is that there is no connection. “You are safe to wear a mask,” Stout said. “You should wear a mask.”

Editor’s note: FactCheck.org is one of several organizations working with Facebook to debunk misinformation shared on social media. Our previous stories can be found here.


Centers for Disease Control and Prevention. “About Cloth Face Coverings.” Updated 28 Jun 2020.

Fichera, Angelo, et al. “The Falsehoods of the ‘Plandemic’ Video.” FactCheck.org. 8 May 2020.

Fichera, Angelo. “Video Presents Flawed Test on Masks, Oxygen Levels.” FactCheck.org. 2 Jul 2020.

Hale Spencer, Saranac. “Meme Misconstrues Efficacy of Face Masks in Spread of COVID-19.” FactCheck.org. 9 Jul 2020

Hale Spencer, Saranac. “Video Misrepresents the Science Behind Face Masks.” FactCheck.org. 24 Jul 2020.

Stout, Janet. President and director, Special Pathogens Laboratory. Telephone interview. 12 Aug 2020.

World Health Organization. “Legionella and the prevention of legionellosis.” 2007.

Hale Spencer, Saranac. “COVID-19 Isn’t Caused by Bacteria.” FactCheck.org. 27 May 2020.

Centers for Disease Control and Prevention. “Legionnaires’ disease.” 18 Jul 2016.

The COVID Tracking Project. US Daily Cumulative Totals. Accessed 12 Aug 2020.

Centers for Disease Control and Prevention. Legionella — History, Burden, and Trends. 30 April 2018.