Three guests who stayed at a downtown Atlanta hotel were discovered to have come down with Legionnaires’ disease.

The guests were staying at a Sheraton hotel in downtown Atlanta while attending a convention taking place near the hotel. Near the end of the convention, several guests started complaining to hotel staff about lung problems. Those guests ended up being diagnosed with Legionnaires shortly after that.

The CDC defines Legionnaires as a lung infection caused by Legionella bacteria that can be found in warm water. The bacteria can find its way into someone’s body by consuming water or breathing in a mist that contains the bacteria.

The guests’ shared diagnosis has prompted an investigation by the Georgia Department of Public Health that began on Monday.

“Based on epidemiological evidence we have an outbreak among people who stayed at the Sheraton Atlanta during the same time period,” Department spokesperson Nancy Nydam told the press on Tuesday.

To avoid any more potential infections, the Sheraton has closed until the source of the infection is discovered and dealt with. This has resulted in 400 guests being relocated from the Sheraton to other nearby hotels amid the investigation.

The Sheraton released a statement Monday that read:

“The health and safety of our guests is our greatest priority. We are working closely with public health officials and outside experts to conduct testing to determine if Legionella is present at the hotel. As a result, out of an abundance of caution we have made the decision to close the hotel while we await the results.  The Sheraton Atlanta is currently working to relocate its guests to nearby hotels. It is also reaching out to guests with upcoming reservations to assist in directing them to other nearby hotels. Guests whose reservations have been canceled will receive a full refund.”