Pontiac fever is caused by the legionella bacteria, the same bacteria responsible for Legionnaires’ disease. Pontic fever is milder and those affected experience flu-like symptoms, including fever, headaches and muscle aches but sufferers do not go on to develop pneumonia.

It is not known why some people go on to develop the more serious Legionnaires’ disease whilst others get Pontiac fever and some people do not get ill at all. Pontiac fever often infects previously healthy and young individuals.

People with Pontiac fever generally recover in 2–5 days and often without the need for medication. Outbreaks are not common but have been linked to the inhalation of the bacteria found in spa pools according to Public Health England.