Bronchiolitis is a disease of small bronchioles with increased mucus production and occasional bronchospasm, sometimes leading to airway obstruction. It is most commonly caused by a viral lower respiratory tract infection. Bronchiolitis is most commonly seen in infants and young children, with most severe cases occurring among infants. Bronchiolitis is potentially life-threatening.
Respiratory syncytial virus (RSV) is a primary cause ofbronchiolitis, followed in frequency by human metapneumovirus, parainfluenza viruses, influenza viruses, adenoviruses,rhinoviruses, coronaviruses, and, infrequently, Mycoplasma pneumoniae. Viral bronchiolitis is extremely contagiousand is spread by contact with infected respiratory secretions. Although coughing produces aerosols, hand carriageof contaminated secretions is the most frequent mode oftransmission.
Bronchiolitis is a leading cause of hospitalization of infants. Bronchiolitis occurs almost exclusively during the first 2 years of life, with a peak age at 2 to 6 months. Many healthy children with bronchiolitis can be managed as outpatients; however, premature infants and children with chronic lung disease of prematurity, hemodynamically significant congenital heart disease, neuromuscular weakness, or immunodeficiency are at increased risk of severe, potentially fatal disease. Children acquire infection after exposure to infected family members, who typically have symptoms of an upper respiratory tract infection, or from infected children in day care. In the United States, annual peaks are usually in the late winter months from December through March.
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Bronchiolitis caused by RSV has an incubation period of 4 to6 days. Bronchiolitis classically presents as a progressive respiratory illness similar to the common cold in its early phasewith cough and rhinorrhea. It progresses over 3 to 7 days tonoisy, raspy breathing and audible wheezing. There is usually a low-grade fever accompanied by irritability, which mayreflect the increased work of breathing. In contrast to the classic progression of disease, young infants infected with RSV may not have a prodrome and may have apnea as the first signof infection.
Physical signs of bronchiolar obstruction include prolongation of the expiratory phase of breathing, nasal flaring, intercostal retractions, suprasternal retractions, and air trapping with hyperexpansion of the lungs. During the wheezing phase, percussion of the chest usually reveals only hyperresonance, but auscultation usually reveals diffuse wheezes and crackles throughout the breathing cycle. With more severe disease, grunting and cyanosis may be present.
Routine laboratory tests are not required to confirm the diagnosis. It is important to assess oxygenation in severe cases of bronchiolitis. Pulse oximetry is adequate for monitoring oxygen saturation. Frequent, regular assessments and cardiorespiratory monitoring of infants are necessary because respiratory failure may develop precipitously in very tired infants even though blood gas values taken before rapid decompensation are reassuring.
Antigen tests (usually by immunofluorescence or enzyme-linked immunosorbent assay [also referred to as ELISA]) of nasopharyngeal secretions for RSV, parainfluenza viruses, influenza viruses, and adenoviruses are sensitive tests to confirm the infection. Rapid viral diagnosis also is performed by polymerase chain reaction. Identifying the viral agent is helpful for cohorting children with the same infection but is not necessary to make the diagnosis of bronchiolitis.
Chest radiographs frequently show signs of lung hyperinflation, including increased lung lucency and flattened or depressed diaphragms. Areas of increased density may represent either viral pneumonia or localized atelectasis.