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Croup

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Croup is a common respiratory infection that affects the upper airway of children. It is most often caused by a viral infection. This infection leads to swelling inside the larynx, the voice box, and the trachea, which is the windpipe. This swelling can interfere with normal breathing. It often produces a distinctive barking or brassy cough. It also causes a hoarse voice and a noisy breathing sound called stridor. While most cases are mild, croup can sometimes be severe.

The process of croup begins when a virus enters the respiratory system. The body responds by sending white blood cells to the area to fight the infection. These cells include histiocytes, lymphocytes, plasma cells, and neutrophils. As these cells move into the tissues, they cause inflammation and swelling. This swelling occurs in the larynx, the trachea, and the large bronchi. The narrowed airway creates a physical obstruction for air. When air tries to pass through this tight space, it becomes turbulent. This turbulence creates the noisy, high-pitched sound known as inspiratory stridor.

There are different types of croup based on their cause and symptoms. Viral croup, or acute laryngotracheitis, is the most common form. It is frequently caused by the parainfluenza virus, specifically types 1 and 2, in about 75% of cases. Other viral causes include influenza A and B, measles, adenovirus, and respiratory syncytial virus. Spasmodic croup is also caused by these viruses but lacks typical infection signs like fever. In contrast, bacterial croup is much rarer but often more severe. This category includes conditions like laryngeal diphtheria and bacterial tracheitis. Bacterial tracheitis often starts as a viral infection but then develops secondary bacterial growth.

Medical professionals have studied croup for many centuries. The name comes from the Early Modern English verb "croup," meaning to cry hoarsely. The noun for the disease originated in southeastern Scotland. In 1765, physician Francis Home published a famous treatise about its nature and cure. People in ancient Greece knew about a version of croup caused by diphtheria. However, it was not until 1826 that Bretonneau differentiated viral croup from diphtheria. This discovery helped doctors understand that many different germs could cause similar symptoms.

Croup is a widespread condition that affects approximately 15% of children. It most commonly occurs in children between six months and five years of age. It can occasionally be seen in children as old as fifteen. The condition is slightly more common in males than in females. It also shows an increased prevalence during the autumn months. To measure how sick a child is, doctors may use the Westley score. This system assigns points based on five factors: level of consciousness, cyanosis, stridor, air entry, and chest wall retractions. A score of 2 or less indicates mild croup, while a score of 12 or more indicates impending respiratory failure.

Diagnosis is usually based on a physical exam of the signs and symptoms. Doctors often work to rule out more dangerous conditions first. These include epiglottitis, which is an infection of the epiglottis, or an airway foreign body. Sometimes, a frontal X-ray of the neck is used to look for the "steeple sign." This sign shows a narrowing of the trachea that looks like a church steeple. However, this sign is absent in half of all cases. Doctors generally avoid unnecessary blood tests or cultures because the stress of these tests can make a child more agitated. Agitation can actually worsen the airway obstruction.

Treatment depends heavily on the severity of the symptoms. Most mild cases are managed at home with supportive care. This includes resting and keeping the child hydrated. For moderate to severe cases, doctors often prescribe corticosteroids like dexamethasone. A single dose of steroids given by mouth is often very effective. These medicines can start helping as early as two hours after they are given. In more severe instances, doctors may use nebulized epinephrine to temporarily reduce swelling. About one to five percent of cases require hospitalization for observation. While most croup is viral, doctors may use antibiotics if they suspect a secondary bacterial infection.

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