A man has died from a suspected case of Legionnaires' disease.
The 77-year-old from Whitchurch, Shropshire, was admitted to the Royal Shrewsbury Hospital on Monday. He died on Thursday.
The hospital has sent samples to the Legionella reference laboratory for testing. Three men earlier admitted with the disease are recovering.
A hospital spokesman said an investigation into the sources of the disease was continuing.
The patient who died had been out of the country for one week in the middle of August but the inquiry is assuming the infection could have been caught locally.
Dr Rob Carr, consultant in communicable disease control, said: "Clusters of Legionnaires' disease were reported throughout the country during July and August and it may well be possible that our local cases have been due to some common underlying reason, such as unusual weather conditions.
"We just don't know."
It was comforting to learn the number of cases reported nationally and locally had reduced, he added.
"Legionnaires' disease cannot be passed from person to person, but is usually caught by inhaling fine mists of water contaminated with the organism.
"We have looked at possible sources such as water towers in localities where patients lived and worked without finding any obvious cause of infection."
Early symptoms of Legionella are flu-like with muscle ache, tiredness, headache, dry cough, breathlessness and fever that can lead to pneumonia.