BANGOR, Maine (AP) The Maine Center for Disease Control is trying to determine if four cases of Legionnaires’ disease are connected in the Bangor area, officials said Thursday.

The Maine CDC alerted health care providers after learning of four cases in which patients were hospitalized, and there could be more cases, officials said.

The Legionella bacteria, which is found naturally in freshwater environments like lakes and streams, becomes a problem when it grows and spreads in air conditioning systems, hot tubs, fountains and large plumbing systems.

Legionnaires’ disease, which is a type of pneumonia, results when individuals breathe droplets of water containing the bacteria. It’s treated with antibiotics.

Legionella cases are growing in the United States. About 9,000 cases were reported in 2019. Maine has averaged about 21 cases per year since 2016.