Overview

Bronchiolitis is a viral infection that affects the small airways of the lungs called “bronchioles”. It is most likely to occur in younger children (aged 2 and under). Although this infection is usually mild and treatable, in some cases it can become serious and lead to severe complications. Asthma, COPD (chronic obstructive pulmonary disease), pneumonia, respiratory failure, consistent wheezing, and bronchitis are all likely secondary illnesses from having severe bronchiolitis. 

In this article, we will explain the potential respiratory conditions that can develop from severe cases of bronchiolitis, such as asthma and COPD. Genetic predispositions and environmental factors influencing these outcomes are also discussed, and helpful interventions that can be used to prevent bronchiolitis are outlined. 

Understanding bronchiolitis

Most commonly caused by the virus: respiratory syncytial virus (RSV), bronchiolitis is a lower respiratory tract infection targeting the bronchioles. It causes swelling and overproduction of mucus, leading to airway blockages. 

Other known viruses that cause bronchiolitis include:

• The common cold (rhinovirus)
• Adenovirus
• Influenza (flu)
• Metapneumovirus
• It is important to note that bronchiolitis differs from bronchitis, which has been found to infect patients above the age of 2 (teenagers and adults).

Bronchiolitis diagnosis

Due to their developing weaker immune systems, one in three babies under 1 gets infected, primarily due to their weak developing immune systems.

Symptoms of RSV (which causes bronchiolitis) can be seen through physical examinations conducted by a healthcare provider. These symptoms and physical examinations include: 

• Runny nose
• Fever
• Appetite loss
• Chesty cough
• Checking vital signs
• Auscultation (listening to the sound of the heart and lungs) 
• Nasal swabs (using nasal mucus to detect viruses in the body)

Based on these examinations and the symptoms seen, RSV can be detected, leading to a diagnosis of bronchiolitis. 

Potential complications of bronchiolitis

Acute (short-term /mild) bronchiolitis

Symptoms for bronchiolitis (listed above) are similar to a common cold, however, mild bronchiolitis gets better on its own. Some at-home treatments include:

• Children’s paracetamol or ibuprofen for pain
• Saline or salt water to unblock the nasal cavity
• More severe cases of bronchiolitis generally last longer and become progressively worse.

Severe (long-term) bronchiolitis 

Severe bronchiolitis symptoms are seen in three per cent of children who are infected and result in hospitalisation, where treatments include IV, feeding tubes and oxygen. Symptoms include:

• Severe wheezing 
• Respiratory distress
• Laboured breathing 
• Difficulty swallowing
• Dehydration (dry mouth, crying without tears, and decreased urine)
• Blue or pale tinge to their skin, lips, tongue, and nails
• Temperature of 38 degrees or above for children 3 months old or younger
• Recurrent respiratory infections after immediate recovery

The patients who exhibit severe symptoms have a three to four times higher likelihood of developing and being diagnosed with asthma in the next 10 years.⁶ 

The recurrent respiratory infections after immediate recovery also increase the likelihood of long-term respiratory conditions being developed.

Long-term respiratory conditions

Asthma

Severe persistent symptoms of viral bronchiolitis have been linked to the onset of childhood asthma, as it is a major risk factor for asthma development. Severe recurrent bronchiolitis permanently damages cells in the airways, and this causes the airways to become over-sensitive and inflamed. As a result, symptoms such as shortness of breath, wheezing, coughing and chest pain that are consistent in infancy from bronchiolitis, contribute to the onset of asthma.^1,2 Other factors that contribute to its development include environmental and genetic predispositions such as allergies, the strength of the immune response in the infant, nutrition levels, and vitamin D deficiency. 

Chronic obstructive pulmonary disease (COPD)

Also known as emphysema, COPD is another respiratory condition that bronchiolitis is likely to develop into. Early stages of growth in utero and childhood, as well as recurrent respiratory infections (bronchiolitis), are major influences of COPD in early life events. These factors limit lung development hence triggering harmful respiratory conditions later on in life, most commonly, asthma and COPD.

Bronchiolitis specifically limits airflow by inflammation of the cells in the airways. As a result, this narrows and constricts the bronchus and trachea. Throughout adolescence and adulthood, the onset of COPD can cause the lungs to get damaged and clogged with phlegm, causing respiratory distress, coughing, and many symptoms similar to asthma.³

Pneumonia

Commonly caused by bacterial or viral infections, coughing with phlegm or pus, fevers or severe fluctuating temperatures, wheezing and laboured breathing arise in patients younger than 2 or older than 65. There is also an increased likelihood of getting pneumonia if a patient has asthma, COPD, recurrent respiratory conditions, or a weakened immune system. However, pneumonia is less commonly developed than asthma or COPD after bronchiolitis.

Other common respiratory conditions

• Bronchiectasis
• Recurrent wheezing 

Factors affecting long-term respiratory conditions

Genetic predisposition

There is a clear association between developing severe bronchiolitis and an individual's genetics. Around 20% of the likelihood of developing severe bronchiolitis is based on genetics. It has been specifically localised to immune genes that are less expressed. They code for vitamin D and immune cells in the body; therefore, by decreasing their expression, vulnerability to developing bronchiolitis is increased. This also means that developing respiratory conditions as a result of being infected with RSV is also increased.⁴

Environmental factors

Since 20% of vulnerability to bronchiolitis is based on genetic predisposition, the remaining 80% is based on external environmental factors. Factors such as:⁵

• Second-hand smoke 
• Pollution
• Exposure to allergens (to the child during infancy and to the mother during pregnancy)
• Overcrowded and unhygienic living conditions
• Premature birth
• Lack of breastfeeding 

Severity of the initial infection  

Severe bronchiolitis has been associated with recurrent wheezing and asthma development in later stages of children's development. The severity of bronchiolitis plays a role in the development of conditions later on in life. The more severe and recurrent the initial infection in the infant is, the higher the chance of developing respiratory conditions, especially if the RSV infection is severe enough to require hospitalisation of the infant.¹⁶

How to prevent bronchiolitis?

• Vaccinations against influenza are an important preventative measure and quite an impactful one since influenza is a leading cause of viral bronchiolitis
• Breastfeeding reduces infants' vulnerability to respiratory infections since vital nutrients and resistant proteins are passed into children during breastfeeding. These proteins can provide immunity against bronchiolitis and prevent recurrent respiratory infections from occurring
• Another form of prevention is simply maintaining hygienic and well-sanitised conditions. This includes washing hands with antibacterial soap, hand sanitising, and preventing inhalation of smoke
• Bronchiolitis is easily transmitted through the air, so a consistent clean air environment is helpful in preventing the virus from spreading, transmitting or worsening into any long-term harmful respiratory condition⁷ 
• Washing and cleansing toys regularly, and covering mouths when coughing or sneezing, also prevent the transmission of any respiratory viruses

Summary

Severe recurrent bronchiolitis in children under the age of 2 can result in sustaining long-term respiratory conditions such as asthma, COPD, pneumonia, bronchiectasis and recurrent wheezing. 

Bronchiolitis is caused by RSV, which develops when viruses or bacteria, such as rhinovirus (common cold), influenza, adenovirus and many more end up manifesting similar symptoms. These symptoms include a runny nose, fever, loss, chesty cough and respiratory distress. This results in long-term or short-term bronchiolitis. On most occasions, bronchiolitis can go away on its own, however, severe RSV infections result in hospitalisation and an increased likelihood of developing respiratory diseases later on in life.

Factors can be controlled to limit the severity of bronchiolitis and prevent its transmission, such as maintaining a hygienic clean air environment around newborns and infants, breastfeeding for a long enough period and ensuring all people who are around infants are up-to-date with vaccinations.