Croup overview
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
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Overview
Croup is a respiratory disease which afflicts infants and young children, typically aged between 3 months and 3 years. The respiratory symptoms are caused by inflammation of the larynx and upper airway, with resultant narrowing of the airway.
Historical Perspective
Diptheritic croup reports date back to the Homer-era of Ancient Greece, speculating to have emerged in the 12th century B.C.E. The Viral-based croup was discovered in 1826 by French medical doctor Pierre Bretonneau. Initial therapies included cold water mist to soothe pain as well as tracheotomy for patients with severe cases requiring hospitalization. In the 1970s, nebulized Epinephrine emerged as a therapy. Glucocorticoid therapies emerged in the late 1980s' and 1990's. Preventative therapy emerged with successful Immunization of individuals against diptheritic croup with the development of influenza and diptheria vaccines.
Pathophysiology
Development of croup results from infiltration of white blood cells through the human parainfluenza virus (HPIV). HPIV expels its nucleocapsid into the recipient cell cytoplasm. The viral transcription then occurs through the HPIV RNA-dependent RNA polymerase. The viral [Messenger RNA|mRNAs] are translated into viral proteins, leading to the replication of the genome into the negative-sense RNA strand, which is then encapsidated by the nucleoprotein and used for further transcription and replication. The inflammation response to HPIV occurs from the up-regulation of cytokines and the released Immunoglobulin E inhibiting histamine. The resultant swelling of the larynx, trachea, and large bronchi obstructs the airways obstruction which leads croup.
Causes
Human parainfluenza virus is an enveloped, single stranded negative sense RNA virus with four distinct serotypes. The virus genome consists of approximately 15,000 nucleotides used to encode six structural proteins; they function to attach, enter, and fuse with the host cell, forming a complex with the RNA genome. Human parainfluenza virus is a member of the paramyxoviridae family. It is a member of one of two genuses depending on the serotype: respirovirus or rubalavirus. Human parainfluenza virus infects the body by infiltrating white blood cells. It is transmitted through respiratory droplets through the air, as well as physical contact with an infected individual or contaminated physical surface.
Classification
Croup is classified by severity of symptoms. The Westley Score system quantifies symptoms from a score of 0-5. The sum of the symptom score stratifies croup into mild, moderate, severe, or indicative of total respiratory failure.
Epidemiology and Demographics
Annually, the incidence of croup is approximately 532/100,000 individuals, peaking in the fall of each year. Croup is primarily found in children between 6 months and 6 years of age, but rare cases have been reported in children as young as 3 months and as old as 15 years. Males are 1.5 times more likely to develop croup.
Natural History, Complications and Prognosis
Croup symptoms typically manifest after 2-7 days of human parainfluenza virus infection. Symptoms will typically last between 24-48 hours; very rarely they will last up to 7 days. They will typically resolve without treatment, excepting the most severe cases that pose the threat of respiratory failure. Prognosis is good in mild and moderate croup with and without treatment. Severe croup and impending respiratory failure classifications have poor prognosis, if left untreated, due to life-threatening airway obstruction. With treatment, all manifestations of croup have a good prognosis. Complications of croup stem from airway obstruction, including respiratory failure and respiratory distress. They also stem from infections due to immunocompromise from the causative human parainfluenza virus and corticosteroid therapy; these include bacterial tracheitis, atelectasis, pneumonia, pulmonary edema, and epiglottitis.
Treatment
Primary Prevention
Wash your hands frequently and avoid close contact with those who have a respiratory infection.
The diphtheria, haemophilus influenzae (Hib), and measles vaccines protect children from some of the most dangerous forms of croup.
References