What Is It?
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 and spasmodic croup.
Infectious Croup 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, usually in the fall and winter when people spend more time indoors. Under these conditions, the virus spreads easily through tiny droplets with coughing and sneezing. It also can travel on dirty hands and on things that have been soiled by fluids from a sick person's nose or mouth. These include dirty tissues, shared toys and contaminated drinking glasses and eating utensils.
Once the virus enters the body, it usually begins to attack the upper parts of our breathing system. For this reason, a child with croup may first complain of cold symptoms, such as a runny nose or nasal congestion. The child also may have a low-grade fever or a mild sore throat. Later, as 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 Spasmodic croup is thought to be caused by an allergic reaction, where the linings of the voice box and trachea are swollen but do not show signs of infection. In some cases, the airway irritation seems to be triggered by stomach acid that has come back up into the throat.
Spasmodic croup tends to start suddenly, without any cold symptoms. It usually does not cause a fever.
In the United States, infectious and spasmodic croup account for about 15 % of all respiratory illnesses seen by pediatricians. Infectious croup is most common in children younger than age 6, and boys are affected slightly more often than girls. Spasmodic croup usually affects children who are between 3 months and 3 years old. Before the age of 3 months, a child's risk of either type of croup is fairly low. This is probably because protective antibodies pass from the mother to the child before birth or in breast milk.