Croup is most commonly caused by a virus. It is sometimes, but rarely, caused by bacteria, allergies, or reflux from the stomach. Viruses that are known to cause croup are:
- Parainfluenza virus
- Respiratory syncytial virus (RSV)
- Influenza virus
- Adenovirus
- Enteroviruses
Croup is spread through direct contact with a person, or fluids from another person who has the disease. The infection starts in the nose and throat and moves into the lungs. Swelling affects the area around the voice box (larynx) and into the windpipe (trachea).
Facts and risks of croup
Younger children are more affected by croup because their airways are smaller. Therefore, a small amount of swelling can make it really hard for a child to breathe.
- Croup is most commonly seen in children 3 months old to 5 years.
- The peak time for croup to occur is 2 years old.
- Croup is seen more often in the winter.