Two people are in a critical condition after an outbreak of Legionnaires' Disease in Stoke-on-Trent.
The pair are among 15 people affected by the disease, the Health Protection Agency (HPA) said. All of the victims are aged between their late 40s and mid-70s.
The number of confirmed cases has been steadily rising since news of the outbreak on Tuesday.
Fourteen patients are being treated at the University Hospital of North Staffordshire, including one of those critically ill, while the other has been transferred to Glenfield Hospital in Leicester.
Public and environmental health experts from the HPA, the Health and Safety Executive, the NHS in Stoke and Stoke-on-Trent City Council are investigating the possible source of the outbreak.
The HPA said the outbreak is not hospital-related and the hospital is a safe environment for visitors.
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 www.nhs.uk.
The HPA stressed that there is no need for anyone who is well or only mildly unwell to see their doctor or to have any tests.