CROOKSTON, Minn. (AP) -- The state Department of Health is investigating four recent cases of Legionnaires' disease in northwestern Minnesota.

The department said Friday the four people became ill between Jan. 22 and Jan. 27 after visiting the Crookston Inn and Convention Center. The four did not stay overnight but had visited the hotel.

Investigators are working with the hotel to determine the source of the bacteria. But evidence suggests the source is the hotel's spa.

Hotel management has temporarily closed the spa and pool to guests. The hotel is notifying guests who were at the hotel between Jan. 14 and Feb. 13 that they may have been exposed to the bacteria.

The disease is spread by inhaling fine mist from water sources containing the bacteria. Minnesota had more than 150 cases of the disease reported last year.