CHESTERTON, Ind. (AP) — Two northwestern Indiana schools have been temporarily closed after a school district employee tested positive for Legionnaires’ disease.

Duneland School Corporation officials say Westchester Intermediate School was closed Friday after “traces” of Legionella bacteria were found in its cooling tower, and Chesterton Middle School was shuttered following a similar discovery in its water system.

Both schools were tested after an employee self-reported testing positive for Legionnaire’s disease.

The district’s administration center was also closed in Chesterton, about 45 miles (72 kilometers) southeast of Chicago. District officials say they’re working with a company to address “any environmental hazard to ensure the safety of students and staff.”

Legionnaire’s is a flu-like illness contracted when infected water vapor is inhaled. The elderly and people with weakened immune systems can be particularly susceptible.