A further four people are being treated in hospital for Legionnaires' Disease in Stoke-on-Trent, bringing the total number affected to 15 - with 13 of them at the University Hospital of North Staffordshire.
The Health Protection Agency (HPA) said those affected are aged between their 40s and 70s.
The number of confirmed cases has been steadily rising since news of the outbreak on Tuesday.
One patient is in a critical condition and is being treated at Glenfield Hospital in Leicester.
People who contracted Legionnaires' disease this year are calling for a public inquiry after a fatal outbreak in Stoke-on-Trent.
A second person has died after an outbreak of Legionnaires disease in Stoke-on-Trent.
Officials believe the Legionnaires outbreak at Stoke On Trent can be traced to a hot tub in a Stoke warehouse.