“Few people have heard of Pontiac fever, and yet most are aware of Legionnaires’ disease. It is intriguing therefore to discover that both illnesses are triggered by the same bacterium… called legionella. Pontiac fever is far milder and much less serious than Legionnaires’ disease. Indeed it may be possible for someone to contract Pontiac fever and assume they simply have the flu, since both present with very similar symptoms.  The main difference is pneumonia. Sufferers of Legionnaires’ disease will probably contract pneumonia and are therefore likely to require hospital treatment in order to make a successful recovery. This is why Legionnaires’ is more serious than Pontiac fever, which doesn’t present with this additional illness.  It is good to know that Pontiac fever is not as serious as Legionnaires’ disease. However it is still wise to identify it if at all possible. It may point to an outbreak of Legionnaires’ that could help others get more urgent treatment as a result.”

Legionella Control (https://legionellacontrol.com/legionella/pontiac-fever-legionnaires-disease/)