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Parainfluenza viruses (types 1, 2, 3) account for more than 65% of all cases. The different serotypes have seasonal patterns, with type 1 and 2 occuring in the autumn and being the most common pathogens associated with croup while type 3 is more frequent in the spring and summer and is associated with pneumonia and bronchiolitis.
Infections are rarely associated with high fever and usually last 4 to 5 days. There are no distinctive laboratory abnormalities, and diagnosis is generally made clinically. Chest and neck xray may demonstrate a “steeple sign” from narrowing of the subglottic region. Viral cultures and immunofluorescent rapid antigen identification can be obtained from respiratory secretions. Specific antiviral therapy is not available. Aerosolized epinephrine can be given to severely affected, hospitalized patients to decrease airway obstruction. Parental (>0.3mg/kg) and oral ((0.15mg/kg) dexamethasone have been demonstrated to lessen the severity and duration of symptoms and hospitalization in patients with moderate to severe croup.
References
American Academy of Pediatrics. Parainfluenza viral infections. In: Pickering LK, ed Red Book: 2006 Report of the Committee on Infectious Diseases. 27th ed. Elk Grove Village, Ill: American Academy of Peditrics; 2006