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Bronchiolitis is an acute, febrile, clinical syndrome of infants and young children associated with a lower respiratory tract infection and characterized by cough and wheeze.

I. Etiology and Pathophysiology

The most common cause of bronchiolitis is respiratory syncytial virus (RSV). Other pathogens associated with the disease are parainfluenza and influenza viruses, rhinovirus, adenovirus, and Mycoplasma pneumoniae. Bronchiolitis occurs most often during the winter months in infants under 12 months of age (80%). The natural course of the disease is an upper respiratory tract infection with fever and rhinorrhea that may progress over 2 to 5 days to lower tract involvement with wheezing and some degree of respiratory distress accompanied by tachypnea, nasal flaring, and retractions. In RSV infection the virus invades the epithelial cells of the respiratory tract, moving from upper tract to lower by cell-to-cell transfer. The result is necrosis of the epithelium with subsequent sloughing and obstruction of the small airways. This leads to the characteristic findings of wheezing and hyperinflation.

II. Clinical Course

Two-thirds of children with bronchiolitis will have fever. Physical examination often reveals an irritable infant with tachypnea and tachycardia. Wheezing is the hallmark of the disease. Affected infants may be unable to take adequate oral fluids and become dehydrated. Other complications of bronchiolitis are hypoxemia, respiratory failure, apnea, and bacterial superinfection. Apnea can be a presentation in infants less than 6 months of age. Some of the factors associated with more severe disease include a history of prematurity, young chronologic age, chronic lung disease (especially bronchopulmonary dysplasia), and congenital heart disease. Ten to 20% of infants with bronchiolitis will develop significant respiratory compromise, necessitating admission to the hospital. The mortality for bronchiolitis caused by RSV is 0.5% to 1.5% for hospitalized patients (as high as 37% for infants with congenital heart disease).

III. Evaluation

The outpatient evaluation should begin with a thorough history and physical examination, since bronchiolitis is, for the most part, a clinical diagnosis. A chest x-ray (CXR) is not routinely recommended but should be considered in select cases to rule out other causes of wheezing in this age group, such as foreign-body aspiration, congenital anomalies, or bacterial pneumonia. The CXR will usually show hyperinflation and peribronchial thickening. The presence of atelectasis may indicate a more severe course. Pulse oximetry determination of oxygen saturation may reveal hypoxemia, which is common, even in the absence of clinically detectable cyanosis. If the infant is extremely tachypneic or in moderate respiratory distress, a capillary blood gas should also be drawn to rule out carbon dioxide retention, a sign of respiratory failure. A complete blood count (CBC) is generally not helpful.

IV. Diagnosis

Although bronchiolitis is a clinical diagnosis, a specific etiology can be determined by obtaining a nasal wash from the child for culture and RSV antigen.

V. Treatment

Treatment for most children is largely supportive. Oxygen should be given to those with hypoxia and intravenous fluids to those with inadequate oral intake. The decision to admit a child with bronchiolitis is complex and multifactorial. It should be based on (a) general appearance (whether a child looks toxic or appears happy and playful), (b) age (infants less than 3 months of age or with a history of prematurity with gestational age of less than 34 weeks are at greater risk for apnea and should be closely observed in the hospital), (c) tachypnea (an infant consistently breathing more than 60 to 70 times/minute is likely to tire and needs monitoring), (d) oral intake (if an infant is unable to take adequate oral fluids because of tachypnea or respiratory distress, IV hydration is necessary), and (e) hypoxemia. (Resting oxygen saturation of less than 95% indicates hypoxemia; saturation is likely to decrease with crying or sucking, and such infants should be admitted with supplemental oxygen.)

The efficacy of bronchodilator therapy in bronchiolitis is questionable and depends on the degree of bronchospasm that is present. Some infants with a positive family history for atopic disease may have a significant degree of bronchospasm present, and the current illness represents the first episode of reactive airways disease secondary to lower respiratory tract infection. This cannot be distinguished clinically from bronchiolitis. Other infants have a predominantly viral lower respiratory tract infection component to the disease with little to no bronchospasm present. The latter commonly have significant crackles present on physical examination. Beta-agonist aerosols may be tried and continued if there is improvement with the therapy. Finally, aerosolized racemic epinephrine may have some value, and a trial may be considered in select patients.

Ribavirin is a broad-spectrum antiviral agent that has been used for the treatment of RSV infection in more than 100,000 patients. The drug proved effective in some early studies, but more recent trials question its efficacy. Because ribavirin is expensive and many experts question its efficacy, its use should be limited to children at high risk for severe disease and should be decided clinically on a case-by-case basis. The drug is administered by a small particle generator and may be given over 12 hours per day.

VI. Prevention

RSV has a high potential for spread in the day care and hospital settings. Since the infection is spread from person to person by large droplets of respiratory secretions, the mainstays of prevention are good hand washing and protective masks. The hospitalized patient should be put in contact isolation. The use of goggles and gloves may also help prevent the spread of this agent. Recently, passive immunoprophylaxis with monoclonal antibodies has become available. This is available in an intravenous form, RSV-IGIV, and as an intramuscular preparation, palivizumab. Both preparations have been approved for use in children under 2 years of age for the prevention of RSV disease and are given on a monthly basis during RSV season. Unfortunately, both preparations are extremely expensive and are recommended only to a select group of patients