Understanding Microbronchiolitis in Infants and Young Children

Microbronchiolitis, also known as bronchiolitis, is a common lower respiratory tract viral infection affecting infants and young children under 2 years old. It causes inflammation and blockage of the small airways in the lungs, leading to coughing, wheezing, and difficulty breathing. While typically not life-threatening, understanding the causes, symptoms, and treatment options is crucial for parents and caregivers.

What Causes Microbronchiolitis?

The primary cause of microbronchiolitis is viral infection. The most frequent culprit is respiratory syncytial virus (RSV) CDC. Other viruses that can cause bronchiolitis include:

• Influenza virus
• Coronavirus (including COVID-19)
• Parainfluenza virus

Less commonly, bacterial infections like Mycoplasma pneumoniae, Chlamydia pneumoniae, and Bordetella pertussis can contribute to bronchiolitis.

Why are Infants More Susceptible?

Infants and young children are more prone to microbronchiolitis and experience more severe symptoms than adults for several reasons:

1. Immature Lung Development: The lungs of premature infants are often not fully developed, and even in full-term babies, the small airways are narrower than those of adults. Swelling from inflammation or increased secretions can significantly reduce airflow.
2. Immature Immune Systems: Infants, especially those born prematurely, have underdeveloped immune systems and lack pre-existing immunity to common respiratory viruses, increasing their risk of infection and illness severity.
3. Nose Breathing: Babies primarily breathe through their noses. If the nasal passages are blocked, combined with blockage in the small airways, it can lead to difficulty feeding and hypoxia (low oxygen levels).

How RSV Causes Severe Bronchiolitis

RSV replicates in the nasopharyngeal mucosa and then travels down the trachea, specifically targeting the small bronchi and alveolar epithelium. This causes infected cells to enlarge and multiply, forming “papillary” tissue that obstructs the already narrow airways in infants and young children. Combined with excessive mucus production, this can lead to severe bronchiolitis and worsening symptoms.

Diagnosis of Microbronchiolitis

A doctor will diagnose microbronchiolitis by assessing the infant’s medical history, clinical symptoms, and performing a physical examination, including listening to the lungs. In severe cases or when complications are suspected, a chest X-ray and blood oxygen level measurement may be necessary.

Treatment and Management

Currently, there is no specific antiviral medication to cure microbronchiolitis. Treatment focuses on supportive care to manage symptoms. Most infants and young children will gradually improve within 1 to 2 weeks, even though the cough may persist for up to 3 weeks. Hospitalization may be required if the condition worsens.

When to Seek Medical Attention

Seek immediate medical attention if your child exhibits any of the following symptoms:

• Difficulty breathing or rapid breathing
• Bluish skin color (cyanosis)
• Severe coughing or wheezing
• Dehydration (decreased urination, dry mouth)
• Fever
• Lethargy or unresponsiveness

Source: Yang Wanfeng, consultant pediatrician at Hong Kong Adventist Hospital-Tsuen Wan