Atypical pneumonia is a pneumonia not caused by one of the more traditional pathogens. It can be caused by a variety of microorganisms. When developed independently from another disease it is called Primary Atypical Pneumonia. 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 occurring form of pneumonia. Distinction between atypical and typical pneumonia, however, is medically insufficient. For the treatment of pneumonia it is important to know the exact causing organism. Moreover, S. pneumoniae has become a relatively lesser important cause