An inmate at the Pendleton Correctional Facility has died after being diagnosed with Legionnaire’s Disease.

The Indiana Department of Correction announced an outbreak of the illness at the prison earlier this week and said that five inmates — three with confirmed cases of Legionnaire’s and two with probable cases of the illness — were hospitalized.

Legionnaire’s is a serious type of pneumonia caused by the Legionella bacteria. It is spread through aerosolized water droplets, such as mist or steam, and not through person-to-person contact. It can be treated with antibiotics but is sometimes fatal, according to the Centers for Disease Control and Prevention.

IDOC said Friday it is working to determine the source of the bacteria. Testing is underway and results could take several days.