Snapshot A 4-year-old girl presents to the emergency room for a cold. For the past day, she has had a low-grade fever and has been having increasing difficulty breathing. She has a very loud cough, almost like a seal barking, according to her mother. On physical exam, she has notable inspiratory stridor, accessory muscle use, and a barking cough. She is immediately given a single dose of steroids and given racemic epinephrine with some improvement. Introduction Classification parainfluenza virus an enveloped, nonsegmented, linear (-) single-stranded RNA virus must have its own RNA-dependent RNA polymerase in order to replicate helical structure a paramyxovirus transmission via respiratory secretions Epidemiology demographics causes croup and bronchiolitis in children location lungs Pathogenesis virus has 3 virulence factors hemagglutinin in the membrane binds sialic acid and aids in viral entry into cells neuraminidase helps propagate viral progeny fusion proteins multi-nucleated giant cells helps mediate virus and cell membrane fusion, ultimately resulting in infection of the host cell primarily infects epithelial cells of the nasopharynx and then travels to the airways Associated conditions most commonly causes croup in children, also known as acute laryngotracheobronchitis bronchiolitis in children < 2 years of age pneumonia Prognosis most cases resolve without complications Presentation Symptoms “seal-like” barking cough in croup difficulty breathing Physical exam fever inspiratory stridor accessory muscle use pulsus paradoxus with severe croup and upper airway obstruction Imaging Chest radiography indication all patients findings in croup, may show a steeple sign indicating subglottic narrowing Studies Making the diagnosis based on clinical presentation Differential Acute epiglottitis distinguishing factors patients typically have drooling, high fever, and dysphagia a medical emergency absence of barking cough Treatment Management approach management depends on whether patients have bronchiolitis or croup or pneumonia but centers around supportive care Conservative supportive care indication all patients modalities supplemental oxygen nasal suctioning hydration Medical single dose of steroids indication croup nebulized epinephrine indications croup Complications Respiratory failure Pneumonia