What are the causes of infectious bronchiolitis (inflammation of the bronchioles)?

From the Guidelines

Infectious bronchiolitis is primarily caused by viral infections, with respiratory syncytial virus (RSV) being the most common pathogen, responsible for the majority of cases, as noted in the most recent and highest quality study 1. The causes of infectious bronchiolitis can be broken down into several key points:

• Viral infections are the primary cause, with RSV being the most common etiology, affecting up to 90% of children in the first 2 years of life 1.
• Other significant viral causes include human rhinovirus, human metapneumovirus, influenza virus, parainfluenza virus, and adenovirus, which can also lead to bronchiolitis, although less frequently than RSV 1.
• These viruses are typically transmitted through respiratory droplets when an infected person coughs or sneezes, or through direct contact with contaminated surfaces, highlighting the importance of infection control measures 1.
• Seasonal patterns exist, with RSV infections peaking during winter months in temperate climates, which can help guide preventive measures and resource allocation 1.
• Risk factors that increase susceptibility include young age (especially infants under 6 months), prematurity, underlying cardiopulmonary conditions, immunodeficiency, and exposure to tobacco smoke, which can exacerbate the severity of the disease 1.
• The pathophysiology involves viral invasion of bronchiolar epithelial cells, leading to inflammation, edema, increased mucus production, and necrosis of ciliated epithelial cells, resulting in airway obstruction, air trapping, and the characteristic wheezing and respiratory distress 1.
• While bacterial infections rarely cause primary bronchiolitis, secondary bacterial infections can complicate viral bronchiolitis, particularly in severe or prolonged cases, emphasizing the need for careful monitoring and management of these patients 1.

From the Research

Causes of Infectious Bronchiolitis

The causes of infectious bronchiolitis, which is the inflammation of the bronchioles, can be attributed to several factors, with the most common cause being:

• Respiratory syncytial virus (RSV) 2, 3, 4, 5, 6

Risk Factors

Certain groups are at a higher risk of developing severe bronchiolitis, including:

• Infants less than 6 weeks of age 5
• Prematurely born infants 2, 3, 5
• Infants with underlying cardiopulmonary disease 2, 3, 5
• Infants with immunosuppression 2
• Infants with bronchopulmonary dysplasia 2
• Infants with a history of premature birth 2

Transmission

RSV is transmitted through:

• Contact with respiratory droplets either directly from an infected person 3, 6
• Self-inoculation by contaminated secretions on surfaces 3

Clinical Presentation

The clinical presentation of bronchiolitis typically includes:

• Upper respiratory tract symptoms such as fever, rhinorrhea, and congestion 3, 6
• Lower respiratory tract symptoms such as increasing cough, wheezing, and increased respiratory effort 3, 6