Atypical Pneumonia - Terminology

Terminology

"Primary atypical pneumonia" is called primary because it develops independently of other diseases.
"Atypical pneumonia" is atypical in that it is caused by atypical organisms (other than Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis). These atypical organisms include special bacteria, viruses, fungi, and protozoa. In addition, this form of pneumonia is atypical in presentation with only moderate amounts of sputum, no consolidation, only small increases in white cell counts, and no alveolar exudate. At the time that atypical pneumonia was described first, organisms like Mycoplasma, Chlamydophila, and Legionella still were not recognized as bacteria and instead considered as viruses. Hence "atypical pneumonia" was also called "non-bacterial". In literature the term atypical pneumonia (contrasted with bacterial pneumonia) is still in use, though incorrect. Meanwhile, many of such organisms are identified as bacteria, albeit unusual types (Mycoplasma is a type of bacteria without a cell wall and Chlamydias are intracellular parasites). As the conditions caused by these agents have different courses and respond to different treatments, the identification of the specific causative pathogen is important.