Three cases of Legionnaires' disease in north Shropshire and neighbouring Wales are not thought to be linked, health officials have said.
There appears to be no general health threat, officials say
The three men, from Oswestry and Whitchurch, Shropshire, and Montgomery, Powys, are recovering in hospital after getting the illness last week.
Samples taken from them had not shown there was one cause, said a doctor for the Health Protection Agency (HPA).
There seemed to be no threat to the health of the community, he added.
Dr Rob Carr, consultant in communicable disease control at the HPA, said checks carried out at local cooling towers had also proved negative.
"All the preliminary results indicate that there is no evidence of a common source of legionella infection such as would pose a threat to the health of the wider community in north Shropshire," he said.
"We are now cautiously optimistic that these may have been isolated cases but we will keep looking until we are absolutely certain that there is no single source of these illnesses."
He said the three patients, aged in their 40s and 50s who were being treated at the Royal Shrewsbury Hospital, were showing signs of recovery.
A fourth patient was admitted to the hospital last week with Legionnaires' disease but the infection had been acquired overseas, Dr Carr explained.