MARSHALLTOWN, Iowa (KCRG) – Marshall County Public Health officials said they may never find exactly where an outbreak of Legionnaires’ disease originated. The Iowa Department of Health and Human Services first reported on the illness in the region on September 4. The disease sickened 74 people and killed two. A specific bacteria causes Legionnaires’ disease and can grow in water systems, like large air conditioners.

Linn County Public Health officials said places with stagnant water like hot tubs, humidifiers, or unused shower heads can transmit Legionnaires’ disease if not cleaned properly.

Officials reported the last case six weeks ago, and by late October considered the outbreak over. Marshall County Public Health officials said the Legionnaires’ bacteria likely came from a cooling tower. They tested 12 business centers where people most likely got sick. One center tested positive for the bacteria, but it did not match the strain from infected people.

Officials disinfected all cooling towers and will not count anyone who gets sick in the future as part of this outbreak.