Hundreds of air conditioning units across buildings in Adelaide's CBD and inner-city suburbs are being checked, after a spate of legionnaires' disease cases in the past week.
SA Health's acting chief public health officer Dr Ken Buckett said four men have contracted the disease.
"All four people have been hospitalised and they're receiving the treatment they need," Dr Buckett said.
"It's a very nasty condition ... the symptoms are like pneumonia.
"There's a lot of sputum formed, coughing, you can get feverish, you can get diarrhea."
Dr Buckett said the disease was contracted by breathing in bacteria, which may have been released from air conditioning cooling towers.
"The bacterium that causes the illness lives in a biofilm on the inside of pipes and when water flows through, cooling flows through, they can sometimes be dislodged."
He said the sources of the cases have not yet been found.
"All four cases are in inner-metropolitan CBD and near suburbs, but no common location, no one single place that all four have been to," Dr Buckett said.
"So that makes it a little bit more difficult to track."
GPs have been notified of the spike in cases.
