A confirmed case of Legionnaires’ disease in Stoke-On-Trent, England, has bought the number of patients in the city known to have the disease to 21 in the past three weeks, the Health Protection Agency said today.

A man in his seventies with Legionnaires is recovering in a hospital in the West Midlands city, according to the HPA, which said there are three patients with the disease being treated in University Hospital of North Staffordshire. Legionnaires has caused two deaths in Stoke since the outbreak was first reported July 24. The agency has identified the “probable” source as a hot tub displayed at a store in the town.

The disease is contracted when a person inhales Legionella pneumophila bacteria in small airborne drops of contaminated water from such sources as wet air-conditioning systems that aren’t well maintained. The bacteria multiply at water temperatures of 20 degrees Celsius (68 Fahrenheit) to 45 degrees C and don’t survive above 60 degrees C, according to the Health and Safety Executive, a U.K. watchdog that advises on work- related disease risks.

A cluster of confirmed Legionnaires’ cases was reported in Edinburgh from late May until early July with a total of 50 patients, including three who died.

The disease can’t be spread from person to person, according to the National Health Service. Symptoms occur from two to 19 days after exposure and include a flu-like high fever, muscle pain, a persistent cough and intestinal problems leading to diarrhea and nausea. Elderly people and those with weak immunity are most at risk. It can be treated with antibiotics.