Water samples from cooling towers across the country show signs of bacteria.
Rectangular cooling towers are located under water towers on top of a building in New York City. Photo courtesy Flickr / Creative Commons user Ted McGrath
By Brett Walton, Circle of Blue
Bacteria, responsible for the deadliest water-borne disease in the United States, are common residents of the cooling towers that are part of heating and air conditioning systems in homes, hospitals, nursing homes, hotels, and other large buildings, according to a study from the United States disease control and prevention.
Legionnaires’ disease, Legionella-borne pneumonia, affects thousands and kills hundreds each year in the United States. Cooling towers are involved in numerous outbreaks of the disease because they can spread contaminated droplets over many miles.
It’s a scenario that should affect facility managers across the country, the study’s authors argue.
“Finding the bacteria in all of the regions we have studied makes us aware that Legionella outbreaks are possible anywhere,” said Brian Raphael, CDC microbiologist and co-author of the study, told Circle of Blue.
The bacteria that grow in plumbing systems in warm water target the lungs. Infection occurs when people inhale bacteria that got into the air in the spray from a cooling tower, fountain, shower head, or faucet. The sick and the elderly are at greatest risk – and that risk appears to be increasing. Reported cases of Legionnaires’ disease have risen sharply, quadrupling in the United States since 2000, according to the CDC.
The study was released when the National Academy of Sciences launched an investigation to reduce the risk of Legionnaires’ disease next month and a string of infections at an Illinois state veterans home alerted the governor and one of the U.S. senators to the disease State.
Bacteria are common in cooling towers
The study raised a fundamental question: How common is Legionella in cooling towers? Despite the increasing number of reported cases of Legionnaires’ disease, Raphael says there is a lack of basic data on the prevalence of bacteria in cooling towers. What researchers learn is usually what they discover when something goes wrong.
“Much of what we know is based on our research into outbreaks,” said Raphael. A widespread New York City outbreak in 2015 that was attributed to a cooling tower in the hotel prompted the CDC to take a closer look at the bacterial communities during the day-to-day operation of building water systems.
The researchers analyzed water samples taken as part of routine maintenance tests from 196 cooling towers in the United States. The cooling towers were located in eight of the country’s nine climatic regions as defined by the National Oceanic and Atmospheric Administration. The only region that was not represented was the northern lowlands.
The analysis, published December 20 in the journal PLOS One, took place in two steps. First, the researchers tested the samples for Legionella DNA. Six out of seven cooling towers tested positive.
DNA isn’t the whole picture, however. Its presence is like a footprint that indicates the bacteria were there, but not whether they are active. You may have been killed by a disinfectant that was used to protect the water system from such pathogens.
Next, Raphael and his colleagues used a culture test to see if the bacteria were alive. Almost half of the DNA-positive samples contained Legionella that could be grown in a Petri dish.
Results show Legionnaires’ disease outbreaks can occur anywhere, according to Christopher Boyd, manager of building water health at NSF International, a body that sets industry standards.
“The CDC study helps dispel any myth that cooling tower risks are isolated,” said Boyd, who was not involved in the study, told Circle of Blue. “We see a wide segment of viable legionella systems that need to be addressed and managed.”
Boyd, who led the New York Department of Health and Mental Hygiene’s response to the 2015 Legionella outbreak, said the study supports the idea that builders and managers need to think about disease prevention. Any place with a vulnerable population is at risk of infection.
“These are preventable deaths,” he said.
How to do this is one of the goals of a study by the National Academy of Sciences beginning next month and sponsored by the CDC, the Environmental Protection Agency, the Department of Veterans Affairs, and the Alfred P. Sloan Foundation.
Known for its authoritative reports on science and public order, the Academy has assembled a panel of experts that includes university scholars, engineers, facility managers and public health officials.
Starting February 8, the committee will meet in Washington, DC, to evaluate strategies to inhibit the growth of Legionella in plumbing and cooling systems, such as the voluntary standards developed by industry groups NSF and ASHRAE. The committee will also review guidelines promoting these practices. The evaluation is expected to take 18 months.
There is still a lot to be done to understand Legionella, said Raphael. Which microbial communities in cooling towers support or hinder the growth of legionella? Can samples that test positive for Legionella DNA but not grow in a culture still transmit the disease?
Perhaps most importantly, understanding why the number of reported cases has more than quadrupled in the past 15 years. The researchers point out a number of factors including better diagnostic tests, an aging and sick American public, poor building design, careless maintenance, or corroded water pipes that act as a breeding ground for bacteria.
Brett writes on agriculture, energy, infrastructure, and the politics and economics of water in the United States. He also writes the Federal Water Tap, Circle of Blue’s weekly round up of US government water news. He is the winner of two Society of Environmental Journalists Reporting Awards, one of the highest honors in American environmental journalism: first place for explanatory reporting for a series on septic tank pollution in the US (2016) and third place for beat reporting in a small market (2014). He received the Sierra Club’s Distinguished Service Award in 2018. Brett lives in Seattle, where he wanders the mountains and bakes cakes. Contact Brett Walton
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