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What is bronchiolitis?

Bronchiolitis is an acute infection of the small airways of the lung called bronchioles. It commonly affects infants and young children under the age of 2.1

What causes bronchiolitis?

Most cases of bronchiolitis are caused by viruses. The respiratory syncytial virus (RSV) and parainfluenza virus being the most common ones. Less frequent are influenza, adenovirus, rhinoviruses, and measles virus. Rarely, the bacteria Mycoplasma pneumoniae can be the cause of bronchiolitis.2

After entering the lung, the virus causes the illness by damaging the lining of the bronchioles. The lining would then become inflamed and swollen, making the airways narrow and difficult for air to pass through. The consequence of this is air trapping in the lungs because the blocking of airflow is more significant during expiration (exhaling)2.


Bronchiolitis most often follows an ear infection, common cold, tonsillitis or a common cold. Its major symptoms appears acutely with increasing rate of breathing, increasing heart rate, wheezing, a hacking cough, and difficulty breathing. In severe cases, there may be cyanosis (becoming "blue" of the lips and/or tongue) because of a low oxygen level in the body. When the patient becomes fatigued, breathing may become shallow and ineffective.3 Sometimes the patient may vomit, so dehydration is not uncommon particularly when there is poor intake of fluids. These symptoms usually last for 7-10 days.4

Clinical signs on physical examination frequently include a chest overexpanded by air trapping, wheezing and crackling noises would be heard using the stethoscope. The chest x-ray would also show feature of overexpanded lungs. If there is severe obstruction of the airways, it may also show areas of collapsed lung units (called atelectasis) and associated patchiness of the lungs.

Infants who are young, pre-term, or have other lung disease are at a higher risk to develop failure for normal gas exchange (oxygen and carbon dioxide) termed respiratory failure. In some cases, the infant may stop breathing, leading to cot death (bronchiolitis being one of the causes for cot death).


Bronchiolitis is a common illness amongst young children, mostly under 2 years with the majority under 6 months of age. In any one year, there is approximately 11 cases out of 100 children in their first year of life,2 but only 0.5-2% of infants would require hospital admission5.


The diagnosis of bronchiolitis is made upon clinical symptoms and the course of the illness, and other investigations are usually not required. However, blood tests to monitor the fluid balance and oxygen level in the body may be necessary. Bronchiolitis sometimes mimics asthma. The diagnosis of asthma is considered in children over the age of 18 months, who present with persistent and frequent symptoms of cough and wheezing. They generally have a family history of asthma and or other allergic disorders.

Children with gastric reflux (acidic stomach contents that are regurgitated) and inhaled foreign bodies can present with bronchiolitis. Appropriate history taking and investigations help to identify these conditions.


Most children with bronchiolitis can be adequately managed at home.

Hospitalisation is usually not required in most cases, unless there is severe difficulty in breathing, or the patient showing signs of low oxygen level, dehydration or fatigue. During the early phase of the illness, close monitoring at hospital are often considered if there is other underlying health problems for example heart disease, poor immune system and underdevelopment of the lung.

Tests in the hospital include monitoring of the levels of oxy

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