State and Marshall County health officials have tested cooling towers as part of their investigation into the ongoing legionella outbreak .

They say they believe a tower is the likely source.

Legionella is a bacteria that is found in nature. It can grow in water systems and spread through water droplets. Cooling towers are one of the spots typically tested.

Caitlin Proctor, an assistant professor at Purdue University and a researcher of organisms in plumbing, says cooling towers are large air conditioners on top of larger buildings.

"Most HVAC systems will have it and larger buildings will have it. You know, your individual homes don't have a cooling tower necessarily, but they do, you know, have condensate from the air conditioners," said Proctor.

Dr. Matthew Donahue, Iowa's State

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