Pneumonia is a lung infection, usually caused by bacteria, fungi or viruses. Some pneumonia is caused by inhalation of liquids or chemicals. If not treated quickly, pneumonia can be severe, especially for those with impaired immune systems, whether young or old. "Walking pneumonia" is a term used to refer to mild pneumonia, which can let you walk around with it. Because walking pneumonia usually feels like a cold or flu, many people don't even know they have it.
pneumonia is a lung infection, usually caused by bacteria, fungi or viruses. Some pneumonia is caused by inhalation of liquids or chemicals. If not treated quickly, pneumonia can be severe, especially for those with impaired immune systems, whether young or old. "Walking pneumonia" is a term used to refer to mild pneumonia, which can let you walk around with it. Because walking pneumonia usually feels like a cold or flu, many people don't even know they have it. 
patients in bed. (picture: Stockbyte / Stockbyte / Getty Images)