Submitted by malahchi t3_1118ssa in askscience
Onetap1 t1_j8et0de wrote
They don't live in mechanical ventilation. They live in tepid water which has nutrients. Anything with warm water is hazardous.
The first case, where it was identified, killed a lot of US Legionnaires (armed forces veterans) at a convention at a hotel in Philadelphia. The source was an evaporative cooling tower, which uses evaporating water to discard waste heat from the air conditioning systems.
The thing about cooling towers is that the water is recycled from a pond in the base of the tower. It collects insects, dust leaves, limescale, etc, nutrients for bacteria. And the water is warm. The bacteria was distributed on the water droplets leaving the tower.
https://en.wikipedia.org/wiki/Legionnaires%27_disease#Epidemiology
navigationallyaided t1_j8fxv76 wrote
Yep, the water used in the cooling tower is the perfect place for bugs to grow and many commercial HVAC systems don’t have HEPA/UV treatment for the air handlers. You can treat the cooling tower water with quats to suppress bacterial/viral growth. Also, the condensate that forms in the air handlers is also ideal for bugs to grow.
The movement in HVAC is to have separate air handlers and only one cooling tower.
David_Warden t1_j8g0ltf wrote
Anywhere that you cannot afford to shut down the cooling you will have more than one cooling tower so you can continue operation if a tower is out of service. (eg Hospital, Critical computer centre, Critical Process)
Highjumper21 t1_j8gzhl8 wrote
I had no idea legionella was named after the outbreak among American legion members and that’s where the legionnaires name comes from. Wow
Onetap1 t1_j8rly4g wrote
It was a tragic irony that they'd survived WW1, WW2, Korea, Vietnam and/or whatever else, only to be killed by contaminated water droplets in the USA.
MidnightSun77 t1_j8hcsmc wrote
And finding out that Legionella was the main cause was also very lucky as the Hotel had started to clean the ventilation shafts before a proper investigation of them had started.
VinhBlade t1_j8h7kfg wrote
I'm curious to hear more about the story. Were the US Legionnaires killed from breathing in what is essentially toxic fumes?
Onetap1 t1_j8hcjsd wrote
https://en.wikipedia.org/wiki/Legionnaires%27_disease#Epidemiology
Elderly men, possibly with a large proportion of smokers or ex-smokers. It had been thought the outbreak was a form of pneumonia.
They inhaled atomized water droplets from the cooling towers that carried the bacteria.
Existing_Display1794 t1_j8kafnv wrote
This is why it’s a good habit to breathe through your nose. I swear that’s why it took me so damn long to get Covid. But now now masks and packed bars I got it once.
JoeFelice t1_j8h8sn4 wrote
Did the bacteria enter the hotel's ventilation system? Aren't they sealed off from each other? I'm picturing my home cooling unit and an invasive element would have to penetrate the metal coil to get into the house, and repeat that to access the air.
oundhakar t1_j8hnw5r wrote
+1 to this. The cooling tower ought to be in the secondary circuit - a refrigerant is used in the primary circuit to cool the air in the evaporator - the inside unit of the air conditioner, and condensed back to a liquid in the condenser, with the heat being removed by the secondary circuit water. The water gets warmed up and then cooled down again in the cooling tower.
Was the party out on the terrace near the cooling towers where the legionnaires were exposed to the cooling tower spray carried by the wind?
Onetap1 t1_j8hqv1t wrote
They probably inhaled contaminated water droplets outside.
There was an outbreak in Cumbria, UK, 15 years or more back and it was random people passing through the vicinity who were infected.
[deleted] t1_j8gqper wrote
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