One common type of pneumonia, formerly called primary atypical pneumonia, is caused by Mycoplasma pneumoniae, a mycoplasma. Epidemics of mycoplasma pneumonia occur in schools and in the military. The most prominent symptom of mycoplasma pneumonia is a violent dry cough. Some patients experience nausea or vomiting.

 Pneumocystis carinii pneumonia (PCP) is caused by a normally harmless fungus that may become deadly in people with impaired immune systems. PCP is the most common cause of death in people with acquired immunodeficiency syndrome (AIDS).