If Legionella Is In Our Rivers And Homes, Why Aren’t We All Getting Sick?

Jun 17, 2016

Legionella bacteria are prevalent in natural bodies of water, but in low enough concentrations so as not to pose a risk to human health.
Credit Flickr user Yale Rosen

Bacteria that cause Legionnaires' disease have been found in two water tanks at Allegheny General Hospital on the North Side.

The hospital tested its water after a cancer patient treated for a respiratory ailment in May was found to have the disease and was readmitted with breathing problems later in the month.

Hospital officials don't believe that patient contracted Legionnaires' because of the hospital's water supply, however, and they've yet to confirm any patients have been infected by the hospital's water.

“We have what’s called a mitigation system that releases copper and silver ions into the water at a certain rate to protect the water systems,” said Sam Reynolds, chief quality officer for Allegheny Health Network. “We also do water samples and culture those. Up until recently, all of those testings have been negative or normal.”

Legionella bacteria occur naturally in ponds and streams, but at low enough concentrations so as not to pose a risk to human health, said Laura Cooley, medical epidemiologist with the Centers for Disease Control and Prevention.

When the bacteria enter the water systems in places like hospitals, hotels and long-term care facilities, they can quickly multiply and cause illness.

“It’s when it gets in these industrial, larger, complex, water systems that it has opportunities to grow or amplify, either in stagnant water, warm water or water that doesn’t have enough disinfectant,” Cooley said.

Though legionella is water-borne, people cannot actually get sick from drinking water tainted with the bacteria. Rather it is water vapor or mist containing the bacteria that is inhaled and ultimately causes respiratory illness in some people.

That vapor often comes from a building’s cooling tower, which is part of the air conditioning system, but it can also come from hot tubs, decorative or drinking fountains or showers.

Reynolds said legionella is also likely present in many home plumbing systems. Spokeswoman Jeanne Clark with the Allegheny County Sanitary Authority said the water treatment plant does not specifically test for legionella but that it destroys other dangerous bacteria with chlorine. However, the bacteria have been shown to be resistant to chlorine in some circumstances. 

“I don’t think there’s any difference (between residential and industrial water systems), it’s just that in the home plumbing it’s not something you monitor for and that you treat,” he said. “That’s because legionella is a very benign bacteria for the healthy person. It’s something that does not affect them; their immune system is able to fight it off without any symptoms.”

Annual cases of legionellosis, which includes both Legionnaire's disease and Pontiac fever, in Pennsylvania. 2016 numbers are preliminary.
Credit Data courtesy of the Pennsylvania Department of Health

Cooley said people age 50 and older, current and former smokers and those with compromised immune systems are at increased risk of developing Legionnaires' disease.

Because hospitals house a high concentration of people with weak immune systems, they are often the sites of outbreaks of Legionnaires' disease and Pontiac fever, a less serious respiratory illness caused by the same bacteria.

The first recognized outbreak of Legionnaires' was at the American Legion’s convention in Philadelphia in 1976. A total of 34 people died after the bacteria made its way into the air conditioning system. Six veterans died of Legionnaire’s at a Veteran’s Administration Hospital in Pittsburgh in 2012.

According to a new report from the CDC, annual cases of Legionnaires' more than quadrupled between 2000 and 2014, from 1,127 to 5,166.

Cooley said this could be due to a number of factors: an aging population, a greater number of people with compromised immune systems and increased testing for the disease. Still, she said the disease is likely under-diagnosed.

“There may be a lot of people who are getting treated anyway for pneumonia with appropriate medication and never get the test run," she said. "So we never actually make the diagnosis of Legionnaires' disease.”

The Associated Press contributed to this report.