The man, who died at Diana, Princess Of Wales Hospital in Grimsby after falling ill in July, taught at Sydney Smith secondary school in Hull, although the school is not part of the investigation.
Inquiries are focused on North East Lincolnshire, whe
re four cases, including that of the Grimsby man, have been discovered this year.
Officials were quick to point out that no link has been found between the school and the disease, or between any of the four cases.
Other outbreaks are also being investigated in Norfolk, Shropshire and Wales.
Dr Terry Matthews, Consultant in Communicable Disease Control with the Health Protection Agency (HPA), said: "The Health Protection Agency has been working with Environmental Health colleagues both locally and in other parts of the UK to look carefully at places the patient had visited in order to identify where he may have come into contact with the Legionella bacteria. At this stage, no source has been confirmed. As a result of our inquiries, we are aware that the patient worked in a school in the Hull area.
"Our investigations have shown no evidence at all of any link between the school and the patient's illness and the school is not being investigated as a potential source."
Six men aged between mid-30s and 70 have been treated at the Norfolk and Norwich University Hospital with the uncommon form of pneumonia.
Environmental health officers and public health directors are working with the HPA to pin down the cause of the outbreak, but have so far drawn a blank.
An HPA spokesman said that detailed case histories have been taken, but the only link at this stage is that all the men have visited Norwich city centre within the last month. He added: "As these people all live in the Norwich area, this may not be significant. We may not find a common cause and it may not have anything to do with Norwich. They may have got it from somewhere else."
Meanwhile, officials said they had found no evidence to suggest that three people being treated in a Shrewsbury hospital for Legionnaires' disease were infected from a common source.
