A woman in her 50s has died and four other people are being treated after contracting Legionnaires' disease.
The woman died at Russells Hall Hospital in Dudley in the West Midlands and the others are recovering at home.
All likely sources of infection had been identified, the Health Protection Agency and Dudley Primary Care Trust said in a statement.
Wet air conditioning systems and cooling towers in the area have been shut down or disinfected, they said.
Health care staff, including GPs, have also been warned to look out for patients developing symptoms.
Valerie Little, director of public health for Dudley, said: "We are taking appropriate precautions to ensure that the spread of the disease is contained.
"There is no possibility of spread from person to person and I would ask anyone who thinks that they have any of the symptoms to contact their GP or NHS Direct."