Bronchiolitis Clinical Presentation

Updated: May 17, 2021
  • Author: Nizar F Maraqa, MD, FAAP, FPIDS; Chief Editor: Russell W Steele, MD  more...
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The history and the physical examination form the primary basis for the diagnosis of bronchiolitis.

Because bronchiolitis primarily affects young infants, clinical manifestations are initially subtle. Infants may become increasingly fussy and have difficulty feeding during the 2 to 5-day incubation period. [1] A low-grade fever, usually less than 101.5°F, and increasing coryza and congestion usually follow the incubation period. In older children and adults, as well as in up to 60% of infants, respiratory syncytial virus (RSV) infection is generally confined to the upper airway and does not progress further. [88]

Over a period of 2-5 days, RSV infection progresses from the upper to the lower respiratory tract, and this progression leads to the development of cough, dyspnea, wheezing, and feeding difficulties. When the patient is brought to medical attention, the fever has usually resolved. Infants younger than 1 month may present as hypothermic. [2] Severe cases progress to respiratory distress with tachypnea, nasal flaring, retractions, irritability, and, possibly, cyanosis.


Physical Examination

Examination often reveals the following:

  • Tachypnea

  • Tachycardia

  • Fever (38-39°C)

  • Retractions

  • Fine rales (47%)

  • Diffuse, fine wheezing

The diagnosis is made on the basis of age and seasonal occurrence, tachypnea, and the presence of profuse coryza and fine rales, wheezes, or both upon auscultation of the lungs. Some practitioners exclude RSV infection in the absence of coryza.

Hypoxia is the best predictor of severe illness and correlates best with the degree of tachypnea (>50 breaths/min). The degree of wheezing or retractions correlates poorly with hypoxia. First-time infections are usually most severe; subsequent attacks are generally milder, particularly in older children.

Apnea occurs early in the course of the disease and may be the presenting symptom, especially in those younger than 2 months of age or those born prematurely. Nonobstructive central apnea occurs during quiet sleep and is associated with increases in the apnea index (the percentage of time the baby spends apneic), apnea attack rate (the number of episodes of apnea per unit time), and apnea percentage (the distribution of episodes of apnea in a given sleep state).

Apnea rarely lasts longer than a few days; however, approximately 10% of apneic patients require intubation and mechanical ventilation. The observation that very few cases of sudden infant death syndrome are attributable to bronchiolitis suggests that most infants with apnea self-stimulate and recover spontaneously. Mild RSV disease in young infants is not an indication for hospitalization to observe for apnea. [89, 90, 91, 92, 93, 94, 95]

In a systematic review, Ralston et al found that the overall incidence of apnea ranged from 1.2% to 23.8% in infants hospitalized with RSV bronchiolitis. [89] Further analysis showed that apnea occurred more commonly in preterm infants (range, 4.9-37.5%) than in full-term infants (range, 0.5-12.4%).

Kneyber et al found that the strongest independent risk factor for RSV-associated apnea was age younger than 2 years. [96] Apnea at admission was found to increase the risk of recurrent apnea. Additionally, the likelihood of mechanical ventilation significantly increased in children who suffered from recurrent apnea.

Using the criteria of (1) full-term younger than 1 month, (2) preterm (< 37 weeks gestational age) and younger than 48 weeks postconceptional age, and (3) observed apnea, Willwerth et al found the incidence of in-hospital apnea to be only 2.7%. [90]

Nonrespiratory manifestations of RSV infections include otitis media, myocarditis, supraventricular and ventricular dysrhythmias, and the syndrome of inappropriate antidiuretic hormone secretion (SIADH). [97, 98]



With bronchiolitis, as with any disease, various complications are possible, including those caused by therapy. In most cases, the disease is mild and self-limited. However, in infants who are immunosuppressed and those with preexisting heart or lung disease, RSV bronchiolitis can result in any of the following [97, 99, 100] :

A possible association with asthma has been reported. [101, 102, 103, 104] RSV infections have been associated with the development of asthma later in life, with an odds ratio of 4.3 in children aged 11 years or younger. However, because virtually all children encounter an RSV infection during the first 2-3 years of life, this association may reflect a multifactorial etiology or a genetic predisposition. A genetic predisposition to wheeze after severe RSV bronchiolitis has been suggested. [13, 80] Other studies suggest that human metapneumovirus (hMPV) or rhinovirus-associated bronchiolitis or coinfection with RSV and hMPV increase the likelihood of developing asthma in later years. [31]

A genetic predisposition to severe bronchiolitis and to subsequent development of asthma is supported by findings of polymorphisms in genes involved in allergy, inflammatory response and innate immunity. [105] In fact, a Danish study of twins found that severe bronchiolitis may be an indicator of a genetic predisposition to asthma and without this disposition, asthma is less likely to develop even if the infant had developed bronchiolitis. [106]

As many as 1% of previously healthy children and 3% of developmentally impaired children with bronchiolitis experience neurologic complications. These include seizures, encephalopathy with hypotonia, irritability, and abnormal tone. The long-term prognosis for these children is still unknown. [107]