“Pneumonia is caused by bacteria, viruses or fungus. There are literally dozens of different causes of pneumonia, grouped by the most common types.

Walking pneumonia, also known as atypical pneumonia, is caused by mycoplasma pneumoniae bacteria. It usually causes cold-like symptoms, in addition to a fever (often low grade) and a hacking cough. It is most common in school-aged children and young adults. , says Annette Cameron, MD, a Yale Medicine pediatrician.

Because this type of pneumonia typically causes milder symptoms, it may go undiagnosed for a while, especially if the child is able to participate in normal activities and isn’t as visibly sick as he or she would be with other forms of pneumonia. “And that’s why it’s called walking pneumonia,”.

Yale Medicine (https://www.yalemedicine.org/conditions/pneumonia)