What is the hallmark symptom of laryngotracheitis (croup)?

The hallmark symptom of laryngotracheitis, commonly known as croup, is the barking cough. This characteristic cough typically sounds like a seal barking and is most often caused by inflammation in the upper airway, specifically around the larynx and trachea. This inflammation leads to narrowing of the airway and the distinctive cough that is often associated with croup.

The barking cough, combined with other symptoms such as stridor and hoarseness, helps clinicians diagnose croup effectively and differentiate it from other respiratory conditions.

Other symptoms mentioned, such as substernal retractions, can occur but are not definitive for croup itself. Sticky mucus may be seen during upper respiratory infections but is not specific to croup. Bradycardia is not a symptom related to croup; in fact, tachycardia may be more common in illnesses accompanied by respiratory distress. Thus, the barking cough serves as a clear and essential clinical sign in identifying laryngotracheitis.