Two more cases of Legionnaires' Disease have been confirmed in a city outbreak and one patient is in a critical condition.
A total of 11 people are being treated at the University Hospital of North Staffordshire in Stoke-on-Trent, a number which has been steadily rising since news of the outbreak was released on Tuesday.
All patients are aged between their late 40s and mid 70s, the Health Protection Agency (HPA) said.
The organisation is also investigating two cases identified in early summer as being possibly linked to the current cluster.
A spokesman for University Hospital of North Staffordshire said one of the older patients receiving treatment was in a critical condition, while the others were stable or improving.
Professor Harsh Duggal, director of the Health Protection Agency's Health Protection Unit in Stafford, said: "Our investigation into possible sources continues and we have been able to obtain detailed information on the movements of those affected.
"We are now working with HPA experts in mapping the outbreak and our partners to pinpoint possible sources, using the information we have gathered."
The HPA said the outbreak was not hospital related and the hospital was 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.
An outbreak in Edinburgh came to light at the end of May and is thought to have centred on a cluster of cooling towers in the south-west of the city.
Three people died after contracting the illness and last week the total number of confirmed and suspected cases stood at 101.
The outbreak in Scotland has since been declared over by health officials.
Anyone feeling unwell with any of the possible signs is advised to go and see their doctor, ring NHS Direct on 0845 4647, or visit http://www.nhs.uk.
The HPA stressed that there was no need for anyone who was well or only mildly unwell to see their doctor or to have any tests.