;Legionella pneumophila: Causes a severe from of pneumonia with a relatively high mortality rate.

;Mycoplasma pneumoniae: Usually occurs in younger age groups and may be associated with neurological and systemic (e.g. rashes) symptoms.

;Chlamydia pneumoniae: Mild form of pneumonia with relatively mild symptoms.

Symptoms include pyrexia, shortness of breath, laboured breathing, cough, arthralgia (joint pain), malaise, loss of appetite, confusion, rash, and diarrhoea

Treatment is with antibiotics and diagnosis is confirmed by blood cultures and sputum samples.