Two more cases of Legionnaires' Disease have been confirmed in a city outbreak, bringing the total number of people receiving treatment for the illness to nine.
The Health Protection Agency (HPA) said all those affected are aged between their late 40s and mid-70s and are being treated at University Hospital of North Staffordshire in Stoke-on-Trent.
The organisation said the further two cases brings the total number of patients to nine after news of the outbreak broke on Tuesday.
The HPA is also investigating two cases identified in early summer as being possibly linked to the current cluster.
Professor Harsh Duggal, director of the Health Protection Unit in Stafford, said: "Early microbiology typing results back from the HPA laboratories show that samples taken from some of the patients look very similar so far and this is consistent with the cases having caught their infection from the same environmental source.
"We are taking detailed histories of the movements of the patients to see if there are similar patterns which would indicate a local source of infection. It is important to stress that the outbreak is not hospital- related and the hospital is a safe environment for visitors."
Public and environmental health experts from the HPA, the Health and Safety Executive, the NHS in Stoke and Stoke-on-Trent City Council are working together to identify and investigate possible sources.
Dr Zafar Iqbal, director of public health at the NHS in Stoke, said early symptoms include a flu-like illness with muscle aches, tiredness, headaches, dry cough and fever which can then lead to pneumonia. Patients can become very unwell but the disease can be effectively treated with a course of antibiotics.
"Legionnaires' disease is a rare but potentially life-threatening illness," Dr Iqbal said. "It is caused by a bacteria commonly associated with water systems and cannot be passed from person to person. You cannot catch Legionnaire's disease from drinking water."
Anyone feeling unwell with any of the possible signs is advised to go and see their doctor, ring NHS Direct on 08454647, or visit www.nhs.uk.