What is "atypical pneumonia"

n. an acute respiratory disease marked by high fever and coughing; caused by mycoplasma; primarily affecting children and young adults [syn: primary atypical pneumonia, mycoplasmal pneumonia]

Atypical pneumonia, also known as walking pneumonia, is the type of pneumonia not caused by one of the more traditional pathogens. Its clinical presentation contrasts to that of "typical" pneumonia. A variety of microorganisms can cause it. When it develops independently from another disease it is called primary atypical pneumonia (PAP).

The term was introduced in the 1930s and was contrasted with the bacterial pneumonia caused by Streptococcus pneumoniae, at that time the best known and most commonly occurring form of pneumonia. The distinction was historically considered important, as it differentiated those more likely to present with "typical" respiratory symptoms and lobar pneumonia from those more likely to present with "atypical" generalized symptoms (such as fever, headache, sweating and myalgia) and bronchopneumonia.

Distinction between atypical and typical pneumonia, however, is medically insufficient. For the treatment of pneumonia it is important to know the exact causal organism.