Three school buildings in suburban Chicago will reopen on Monday, days after annual testing of cooling towers found higher-than-normal levels of the bacteria that causes Legionnaires' disease, school officials said.

The buildings, which included a high school, middle school and alternative secondary programs, were closed and 3,000 students and about 350 staff members were moved to other locations on Wednesday "in an abundance of caution," the district said.

"We have no evidence that students or staff were at risk for contracting any illnesses related to these test results," School District U-46, which is headquartered in Elgin northwest of Chicago, said in a statement. The district is the second largest in Illinois, according to its website.

"We believe, and doctors have confirmed, that students and staff were at very low risk of falling ill due the findings in the test results," the district said.

All 19 water cooling towers were cleaned and sanitized, and the district said it has put a plan into place to prevent an incident like this from occurring again. It said it will schedule testing before the school year starts, test and sanitize more often and consult an infectious disease physician.

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Legionnaires' disease is a type of pneumonia caused by inhaling mist infected with the bacteria Legionella. The mist may come from air-conditioning units for large buildings, hot tubs or showers.

The building shutdowns followed Legionnaires' outbreaks that killed a dozen people in New York City; 13 in Quincy, Illinois; and sickened scores of inmates at a California prison.

All but one of the dead in Quincy, a city about 240 miles southwest of Chicago, were residents of a veterans home, the oldest and largest such facility in Illinois, officials said.

Legionnaires' disease in severe cases can lead to respiratory failure, kidney failure and septic shock. It cannot be transmitted person-to-person.