The New Jersey Department of Health says that officials are investigating a cluster of Legionnaires’ disease cases in Union County.

Officials say that there have been 22 confirmed cases as of May 23 throughout the county, including five deaths. Officials say that the people became ill between Mach 8 and May 13.

The five people who died were older adults who had other significant medical conditions, according to officials.

“The risk to any resident of, or recent visitor to Union County is very small,” said state Health Commissioner Dr. Shereef Elnahal in a statement. “Out of an abundance of caution, the department recommends that individuals who live in Union County who become ill with pneumonia-like/respiratory symptoms, such as fever, chills, cough, shortness of breath, muscle aches, and headache visit their health care provider.”

Legionnaires’ disease is a type of lung infection caused by bacteria called Legionella. People can contract Legionnaires’ disease by breathing in small droplets water containing Legionella bacteria. This water can come from air-conditioning units for large buildings, decorative fountains and plumbing systems. Health officials say that people cannot get ill with Legionnaires’ disease by drinking water.

Health officials say that otherwise healthy people exposed to the illness are at a lower risk of developing it. People over age 50, smokers, or those with a weakened immune system have a higher risk.