General Facts and Figures Classification Presentation History Physical Exam Labs Radiology Diagnosis Criteria for diagnosis Differential Microbiology General Specific organisms Pharmacology Drug classes Mechanism of action Resistance Treatment General Site of care Medication Duration Assessment of response Prevention References Literature cited Complete bibliography Links More...		General Classification in the past a distinction was made between typical and atypical pneumonias (typical being those caused by common pathogens and atypical referring to those caused by Mycoplasma pneumoniae, Chlamydia pneumoniae, or Legionella pneumophila); it was thought that the clinical presentations were different and could help identify the etiologic organism but such a classification has not proven to be useful currently pneumonias are defined as either community-acquired (CAP) or nosocomial or hospital-acquired CAP is defined as an infection acquired in the community setting; the definition varies and it may or may not include infections acquired in a nursing home or long-term care facility nursing home-acquired pneumonias are considered by some to be CAP while others classify them as nosocomial aspiration pneumonia is generally considered as CAP unless it occurs in the hospital setting, in which case it is possible that the patient's oropharynx is colonized with aerobic Gram-negative rods (AGNRs) and it should be treated as nosocomial