The bacteria that causes Legionnaires’ disease was found in four different locations at Dallas Fort-Worth Airport, local TV station NBC 5 reported Tuesday. Testing for the bacteria began after an employee said he’d been feeling sick. Legionella bacteria was subsequently located in the water supply at four American Airlines maintenance hangars.

American Airlines installed filters in the hangar’s shower heads and sinks and provided bottled water to stop the spread of bacteria in its tracks. “Nothing is more important than the safety and health of our employees,” American Airlines spokesman Matt Miller told NBC 5. The one sick worker has since gotten better and so far, nobody else has fallen ill.

The Legionella bacteria that causes Legionnaire’s disease is naturally found in freshwater lakes and rivers but it becomes a problem when it makes its way to the public water supply. It breeds in places like plumbing systems, air conditioners and water tanks. Once it’s in the water supply, it transmits itself to humans when it condenses into tiny drops of mist. Those droplets are then breathed in and spread. It’s unusual to contract it from drinking contaminated water, although there have been rare instances of contraction when bacteria contaminated water is aspirated, or goes down the wrong pipe.

Legionnaires' disease is a respiratory infection that causes symptoms such as coughing, fever and chest pain. The fatality rate for Legionnaires’ hovers around 15 percent, according to the U.S. Department of Labor. People who survive the infection usually suffer from long term effects like concentration problems, fatigue and pain, according to Legionella.org.

An estimated 5,000 cases are reported in the United States every year, though that number has been rising as of late, likely due to warming temperatures and aging infrastructure. In the summer of 2015, an air conditioning cooling tower in the Bronx was responsible for a Legionnaires’ outbreak in New York City that left 119 infected and 12 dead.