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The most likely infectious cause of stridor and barking cough in a pediatric patient is parainfluenza virus. This virus is well known to be associated with croup, a common condition in young children that presents with these distinct symptoms. Croup is characterized by inflammation of the upper airway, leading to a narrowing of the airway, which results in stridor (a high-pitched wheezing sound during inhalation) and a barking cough.

Parainfluenza viruses are among the leading causes of viral croup, especially in children under the age of 5. The hallmark symptoms arise due to edema of the larynx, which is precipitated by the viral infection. In croup caused by parainfluenza virus, the cough often sounds similar to the bark of a seal and is usually accompanied by stridor, especially when the child is agitated or active.

In contrast, while Bordetella pertussis can cause coughing fits and can be severe, it typically does not produce the characteristic barking cough or stridor associated with croup. Haemophilus influenzae type B was historically a common cause of epiglottitis, which presents differently than croup. Respiratory syncytial virus (RSV) is primarily