What is the definition or description of: atypical pneumonia?

Atypical organisms. Atypical pneumonia is so called because the causative organisms are not the usual ones associated with most cases of pneumonia. Besides mycoplasma, chlamydia & legionella, many viruses, fungi & protozoa can cause atypical pneumonia as well. Symptoms & signs can be atypical - dry cough, minimal or no fever, absence of lobar consolidation or leucocytosis etc. Also called walking pneumonia.