84% of US cooling towers contain Legionella bacteria

DNA evidence of Legionella bacteria is present in 164 cooling towers throughout eight of the nine climate regions in the United States, according to a study published in PLOS One.

Legionella bacteria can cause a virulent form of pneumonia called Legionnaires' disease. The illness can be contracted by inhaling mist from infected water sources, such as cooling towers, steam rooms and plumbing systems.

As cooling towers have been linked to multiple outbreaks of Legionnaires' around the country, researchers sought to determine the presence of Legionella bacteria in the nation's cooling towers. The team obtained water samples from 196 cooling towers around the nation between July and September 2016 — 84 percent (164) contained DNA evidence of Legionella. Researchers conducted culture tests on Legionella isolates from 78 of the towers. The team identified 144 unique Legionella isolates, 76 of which were Legionella pneumophilia.

"[T]he potential exists for [Legionnaires' disease] cases and outbreaks to occur across the continental U.S. wherever a colonized [cooling towers] and a susceptible population coincide," concluded the study's authors. "However, CT waters specifically associated with outbreaks may have differences in Legionella abundances and types and may contain altered microbial communities compared to our findings. … Detailed examination of the microbiome and physical parameters such as water quality metrics may help elucidate what factors cause Legionella in a CT to shift from environmental bacteria to outbreak pathogens."

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