Bronchiolitis - Symptoms, Causes and Treatment

Bronchiolitis is an inflammation of the bronchioles, one of the deepest regions of the airways of the lungs. Bronchiolitis is usually caused by a viral infection and mainly affects children under the age of 2 years.


What is bronchiolitis?

Pulmonary anatomy
Pulmonary anatomy
The air we breathe in enters the mouth/nose and follows the following path: pharynx → larynx → trachea → bronchus → bronchiole → alveolus (see the illustration on the side for a better understanding).

As we move along the respiratory tree, the structures become more and more branched and thin. The bronchioles are the last part of the respiratory tree before the alveoli, which are the structures that deliver the oxygen breathed into the blood.

The bronchioles are almost microscopic structures with a diameter of less than 1 mm. They are through channels so small that air must pass to reach the alveoli. Any inflammatory process that affects the bronchioles causes swelling in the wall of the bronchioles, closing the passage of air and increasing the production of mucus inside the airways.

Bronchiolitis - inflammation of the bronchioles - translates clinically as bronchospasm (wheezing in the chest) and cough with expectoration.

Causes and risk factors

Bronchiolitis is usually caused by a viral infection, in most cases by a virus called Respiratory Syncytial Virus (RSV). Other viruses may also be responsible, such as Rhinovirus, Influenza, Parainfluenza and Adenovirus. The transmission is made in a similar way to any other respiratory virus such as colds and flu.

Bronchiolitis is a highly contagious infection that attacks children under 2 years of age. Babies under 6 months are the main victims.

RSV is very common and exists worldwide. Virtually every child will have had contact with him until he was three years old. Some develop mild, cold-like pictures, while others, usually younger ones, may have severe pictures requiring hospitalization. Usually, children older than 2 years who come in contact with RSV do not develop bronchiolitis, just a simple cold picture. It is possible to become infected with respiratory syncytial virus more than once, but in general, subsequent infections are milder than the initial infection, especially in older children.

The main risk factors for developing bronchiolitis are:
  • Prematurity
  • Low weight at birth
  • Age less than 3 months
  • Children with previous lung, neurological or cardiac disease
  • Immunodeficiency
  • Passive smoking
  • Daycare
  • Have older siblings who often bring home respiratory infections
  • Living at home crammed with lots of people
  • Cold environments (the virus usually circulates more easily in the winter)


The incubation period for RSV is usually 2 to 5 days. The first symptoms are nonspecific, typical of any cold, with coryza, sneezing, coughing and low fever. In most children, the virus is restricted to the upper airways and the picture does not evolve much from there. In younger children, however, the virus can reach deeper areas of the respiratory tree, attacking the bronchi and bronchioles, leading to bronchiolitis.

In bronchiolitis the symptoms appear after 2 to 5 days of cold, presenting the following picture:
  • Refusal to feed
  • Tiredness to suckle
  • Lethargy and drowsiness
  • Bronchospasm (wheezing in the chest)
  • Persistent cough, which can last for more than 2 weeks

In cases of severe bronchiolitis, the child may present:
  • Respiratory distress, characterized by high respiratory rates, generally above 60 incursions per minute, and use of the abdominal and intercostal muscles during respiration
  • Cyanosis (fingertips and purplish lips)
  • Lowering the level of consciousness

In children younger than 2 months, one of the symptoms of bronchiolitis may be breathing pauses (apnea) of up to 20 seconds.

In most cases, bronchiolitis is a self-limiting disease, with spontaneous resolution after a few days. Peak symptoms usually occur within 5 to 7 days. Complete recovery usually takes 1 to 2 weeks, but can take up to 4 weeks in some cases.

The most serious cases are those in which the baby has difficulty breathing, especially when there are signs of effort to breathe. In general, only 3% of cases require hospitalization.


The diagnosis of bronchiolitis is clinical, based on symptoms and physical examination. In most cases, there is no need for laboratory or radiological exams.


For safety, every infant under 6 months with a respiratory infection should be evaluated by the pediatrician.

As with influenza, there is no specific treatment for bronchiolitis. In milder cases, the treatment can be done at home, with rest, antipyretics and nasal serum. Nebulization with serum may also help. If there is any degree of bronchospasm, nebulization with bronchodilators is indicated.

Antihistamines, decongestants, or antibiotics should not be used to treat bronchiolitis.

Babies who still suckle tend to get more tired, unable to suckle as efficiently. In these cases, offer the chest more often so that it stays well hydrated and fed.

Never smoke near a child, especially during a respiratory infection.

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