Walking pneumonia is an outated term used for cases of pneumonia that do not cause significant disability. The term came into being when hospitalization for pneumonia was more common. People who are affected by walking pneumonia do not require hospitalization and are often able to continue participating in school or work functions. Although these mild cases of pneumonia can be caused by any number of microorganisms, infection with viruses such as influenza and respiratory syncytial virus or atypical bacteria such a Mycoplasma pneumoniae, Chlamydophila pneumoniae, or Legionella pneumophila are the most common causes.