Croup is a common respiratory illness in children that causes a change in breathing with a hoarse voice and a brassy, barking cough. Doctors sometimes call croup laryngotracheitis because it usually involves inflammation of the larynx (voice box) and trachea (windpipe).
Croup often is divided into two broad categories:
Infectious croup is caused by an infection with a virus, bacterium or other germ. In the United States, most cases of croup are caused by a virus. These infections usually occur in the fall and winter when people spend more time indoors.
Under these conditions, the virus spreads easily through coughing and sneezing. It also can travel on dirty hands and on things that have had contact with fluids from a sick person's nose or mouth. These include used tissues, toys, drinking glasses and eating utensils.
Once the virus enters the body, it usually begins to attack the upper parts of the breathing system. For this reason, a child with croup may first complain of cold symptoms. These may include a runny nose or nasal congestion. The child also may have a low-grade fever or a mild sore throat.
Later, the virus spreads farther down the throat. The linings of the voice box and windpipe become red, swollen, narrowed and irritated. This triggers hoarseness, a barking cough, and loud, raspy breathing (stridor).
Spasmodic croup is very similar to infectious croup. It can be triggered by infection, but it isn't caused by infection. It tends to run in families, and may be triggered by an allergic reaction.
Spasmodic croup tends to come on suddenly, without fever. Sometimes it can be hard to tell spasmodic croup from infectious croup.
Infectious croup is most common in children younger than age six. Spasmodic croup usually affects children who are between three months and three years old. Before the age of three months, a child's risk of either type of croup is fairly low.