A 2-year-old boy is brought to the pediatrician by his mother for concern about clear, watery nasal discharge and a "barking" cough for the past 48 hours. She cannot identify any precipitating factors. The child never had symptoms like this and has no significant past medical history. He has not had any recent travel and has received all age-appropriate immunizations. He is at the 42nd percentile for height and 53rd percentile for weight, which is consistent with his last visit. The patient is febrile but otherwise vitals are within normal limits. Physical examination reveals clear rhinorrhea and a high-pitched noise coming from the child as he breathes.
Which of the following is the most likely etiology for this child’s illness?
The correct answer is:
D) A negative-sense, single-stranded RNA virus
This 2-year-old child presenting with acute fever, coryza, and barking cough with stridor most likely has croup (also called laryngotracheobronchitis) caused by the parainfluenza virus (Paramyxoviridae family). Typically, patients are 3 months to 3 years in age. This virus is spread from person to person through droplets via coughing, sneezing, and breathing and is most common during the spring, summer, or fall (though it can occur in the winter as well). The classic finding on x-ray is the "steeple sign," which is narrowing of the trachea in the shape of a steeple. The parainfluenza virus is an enveloped, negative-sense, single stranded RNA virus.
Key Learning Point
The parainfluenza virus is an enveloped, negative-sense, single stranded RNA virus which causes croup characterized by fever, coryza, and barking cough with stridor.
