A second person has died as part of the Legionella outbreak in Marshalltown, the Iowa Department of Health and Human Services announced Monday, Sept. 22.

The person, described as an elderly adult with underlying health conditions, died on Thursday. There have been 71 cases of legionellosis since the outbreak started in late August .

Legionnaires' disease is a severe form of pneumonia from Legionella bacteria. Those bacteria are naturally present in lakes, rivers, ponds, soil and even gardens, but they thrive in warm, stagnant water. More: What is a cooling tower? Equipment could be the source of Iowa's Legionnaires' outbreak

HHS believes cooling towers are "the most likely" sources of the outbreak, though lab testing had not confirmed a direct source. Businesses in the area have di

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