Croup is a common infection of the upper air passages that causes swelling around the voice box, windpipe, and bronchial tubes, setting off a characteristic dog- or seal-like cough and wheezing. Infants and toddlers are most commonly affected, but the illness is not usually serious, and home treatments are generally quite useful.
Viruses such as influenza and adenovirus, and sometimes by bacteria or other pathogens, cause infectious croup. The microbes spread easily through dirty hands, coughing, and sneezing. The virus attacks the upper respiratory system, then travels down the throat. Spasmodic croup lies dormant until it is triggered, but not caused by, infection or an allergic reaction. It often runs in families. This condition manifests suddenly. Sometimes, it is difficult to determine whether a croup case is infectious or spasmodic.
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