Pneumonia is an infection of the lungs that can be caused by viruses, bacteria, fungi and parasites.

Pneumonia is an infection of the lungs that can be caused by viruses, bacteria, fungi and parasites. ... For instance, if a child develops pneumonia from a cold caused by respiratory syncytial virus (RSV), it takes 4 to 6 days for symptoms to appear; for the flu virus, symptoms start after 18 to 72 hours.