Four cases of the disease, a rare form of pneumonia, have been confirmed in the county in the past five weeks.

The two other confirmed cases are currently undergoing treatment.

Tests are being conducted on a further two people who are suspected of having the disease.

Herefordshire Primary Care Trust (PCT) said on Friday that the cases came from the Hereford city area.

Public health officials are urgently trying to establish the source of the outbreak to bring the infection under control and GPs throughout the county have been alerted.

Multiplies quickly

In a statement the PCT said there would normally be around 200 cases of Legionnaires' Disease reported in England and Wales each year, giving Herefordshire an average share of one case every two years.

The disease is caused by a bacteria called Legionella pneumophilia.

Although it is widely distributed in the environment and commonly lives in hot and cold water and air conditioning systems it is normally only found in very small numbers.

But when it gets into warm water it multiplies quickly and can spread through the air in very small droplets.

Breathing in these contaminated airborne particles is the main route of transmission for the disease.

Public health officials stressed that it cannot be caught by one person from another.

"Flu-like"

Early symptoms of the disease include a "flu-like" illness with muscle aches, tiredness, headache, dry cough and fever.

Death occurs in around 10-15 per cent of healthy people who contract the disease.

The PCT statement added: "Urgent medical attention is essential."