What is the most common cause of bronchiolitis?

Most Common Cause of Bronchiolitis

Respiratory syncytial virus (RSV) is the most common cause of bronchiolitis in infants and young children. 1

Epidemiology of RSV Bronchiolitis

• RSV is the predominant viral pathogen causing bronchiolitis, with the highest incidence occurring between December and March in North America, though regional variations exist 1
• Approximately 90% of children are infected with RSV within the first 2 years of life, and up to 40% will experience lower respiratory tract infection during their initial infection 1, 2
• RSV infection does not confer permanent immunity, with reinfections occurring throughout life 1, 3
• RSV bronchiolitis leads to more than 90,000 hospitalizations annually in the United States 1
• Mortality from RSV has decreased significantly over time, from approximately 4,500 deaths annually in 1985 to around 390 deaths in 1999 1

Other Viral Causes of Bronchiolitis

While RSV predominates, other viruses that can cause bronchiolitis include:

• Human rhinovirus 1, 2
• Human metapneumovirus 1
• Influenza virus 1
• Adenovirus 1
• Coronavirus 1, 2
• Parainfluenza viruses 1

Clinical Presentation of Bronchiolitis

Bronchiolitis typically presents with:

• Initial symptoms of rhinitis and cough, which may progress to lower respiratory symptoms 1
• Tachypnea, wheezing, rales/crackles 1
• Use of accessory respiratory muscles and/or nasal flaring 1
• Increased respiratory effort, particularly in severe cases 1
• Symptoms typically begin with 2-4 days of upper respiratory tract manifestations before progressing to lower respiratory involvement 3

Risk Factors for Severe Bronchiolitis

• Young age (especially <6 weeks) 4
• Prematurity 5, 4
• Underlying cardiopulmonary disorders 5, 4
• Immunodeficiency 4
• Male gender 5
• Indigenous status 5
• Exposure to tobacco smoke 5, 6
• Poor socioeconomic factors 5

Prevention and Management

• Prevention through meticulous hand washing is crucial to prevent secondary spread 4
• Palivizumab (a monoclonal antibody) is recommended for prophylaxis in high-risk infants, including those born before 29 weeks' gestation, those with chronic lung disease of prematurity, and those with hemodynamically significant heart disease 1, 3
• Treatment is primarily supportive, focusing on adequate hydration and oxygenation 3, 4
• Bronchodilators, corticosteroids, antibiotics, and epinephrine are generally not recommended for routine use 2, 3

Long-term Implications

• Children with viral bronchiolitis in early life are at increased risk of developing recurrent wheezing and asthma later in childhood 2, 6
• However, no pharmacologic treatment has been proven to prevent this progression 6