DES MOINES, Iowa —

The Legionella outbreak in Marshall County is growing, with 54 confirmed cases and one death, according to Iowa Health and Human Services.

State health investigators are focusing on cooling towers in north-central Marshalltown as the most likely source. State epidemiologist Dr. Matthew Donahue said investigators zeroed in on the towers by mapping where patients spent most of their time.

“The fact that this group of patients all seem to come from that general area, and the fact that they didn’t have any of these other (potential Legionella sources), that really stood out as a strong signal that meant the cooling towers were the most likely thing causing the outbreak,” Donahue said.

Officials identified 12 cooling towers in the north Marshalltown area and tested all of

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