What are the most common viruses responsible for bronchiolitis?

From the Guidelines

Respiratory syncytial virus (RSV) is the most common cause of bronchiolitis, accounting for approximately 50-80% of cases, as stated in the 2014 clinical practice guideline by the American Academy of Pediatrics 1. Other common viral pathogens include human rhinovirus, human metapneumovirus, parainfluenza virus, adenovirus, and influenza virus. These viruses typically infect the respiratory epithelium, causing inflammation, increased mucus production, and edema in the small airways (bronchioles), which leads to the characteristic wheezing, coughing, and respiratory distress seen in bronchiolitis. RSV is particularly prevalent during winter and early spring months in temperate climates, with most children being infected by age 2, as noted in the 2006 diagnosis and management of bronchiolitis guideline 1. The diagnosis is typically clinical, based on symptoms and physical examination findings. Treatment is generally supportive, focusing on maintaining hydration and oxygenation. Antiviral medications are rarely indicated except in severe cases or in immunocompromised patients. Prevention strategies include good hand hygiene and avoiding contact with sick individuals, especially for high-risk infants such as those born prematurely or with underlying cardiopulmonary conditions. Some key points to consider in the management of bronchiolitis include:

• Assessing risk factors for severe disease, such as age less than 12 weeks, a history of prematurity, underlying cardiopulmonary disease, or immunodeficiency 1
• Using clinical scores, such as the Respiratory Distress Assessment Instrument, to assess the severity of disease, although these scores have not been validated for clinical predictive value in bronchiolitis 1
• Considering the use of pulse oximetry to detect hypoxemia, although its effectiveness in predicting clinical outcomes is limited 1
• Avoiding routine radiography in children with bronchiolitis, unless there are signs of a complication or an alternative diagnosis is suspected 1.

From the Research

Most Common Bronchiolitis Viruses

• Respiratory syncytial virus (RSV) is the most common cause of bronchiolitis, accounting for more than 80% of cases during epidemics 2, 3, 4, 5, 6
• Other viruses such as human rhinovirus and coronavirus can also be etiological agents of viral bronchiolitis 5
• RSV is transmitted through contact with respiratory droplets either directly from an infected person or self-inoculation by contaminated secretions on surfaces 4

Characteristics of RSV Bronchiolitis

• RSV bronchiolitis usually presents with two to four days of upper respiratory tract symptoms such as fever, rhinorrhea, and congestion, followed by lower respiratory tract symptoms such as increasing cough, wheezing, and increased respiratory effort 4
• Children at increased risk of developing severe bronchiolitis are those <6 weeks of age, those born prematurely, and those with an underlying cardiopulmonary disorder or immunodeficiency 3
• Approximately 80% of cases occur in the first year of life, and by two years of age, virtually all children have been infected by at least one strain of the virus 3

Diagnosis and Treatment

• Diagnosis of RSV bronchiolitis is typically clinical, and routine use of radiography or viral testing is not recommended 4, 6
• Treatment of RSV bronchiolitis is mainly supportive, including maintaining adequate oxygen saturation, hydration, and nutrition 4, 6
• Therapies such as bronchodilators, epinephrine, nebulized hypertonic saline, corticosteroids, antibiotics, and chest physiotherapy are not recommended 5, 6