Bronchiolitis is a common lower respiratory tract infection that affects babies and young children. The early symptoms are similar to those of a common cold, such as a runny nose and cough. As bronchiolitis develops, it can cause:

• a slight fever (raised temperature)
• a dry and persistent cough
• difficulty feeding

Bronchiolitis is most commonly caused by an airborne virus known as the respiratory syncytial virus (RSV). This causes the smallest airways in the lungs (the bronchioles) to become infected and inflamed (swollen). The inflammation reduces the amount of air entering the lungs, making it more difficult for the child to breathe.

Bronchiolitis is most common in infants who are three to six months old. By two years of age, almost all infants have been infected with RSV and 40-50% will have had bronchiolitis. In the UK, most cases of bronchiolitis occur during the winter months, from November to March, when the viruses that can cause bronchiolitis are more common. It is also possible to get bronchiolitis more than once during the same winter season. 

Outlook

There is no medication to kill the viruses that cause bronchiolitis, but the infection usually clears up within two weeks without any treatment. Most infants can be cared for at home by ensuring they get enough fluid and by monitoring their condition.

Around 3% of infants who are under one year of age and have bronchiolitis will need to be admitted to hospital. This is because they develop more serious symptoms, such as difficulty breathing. However, this is more likely to occur in premature babies (babies born before week 37 of pregnancy) and those born with a heart or lung condition.

Symptoms of bronchiolitis 

The early symptoms of bronchiolitis are similar to those of a common cold. The first symptom is usually a blocked or runny nose. Your child may also have a slight cough or fever (high temperature). A normal temperature is 36-36.8C (96.8-98.2F).

The symptoms of bronchiolitis usually get worse during the first three days, then gradually improve. During this time, your child may experience some of the following symptoms:

• a rasping and persistent dry cough
• rapid or noisy breathing
• brief pauses in their breathing
• feeding less and having fewer wet nappies
• vomiting after feeding
• being irritable

Even though most cases of bronchiolitis are not serious, these symptoms can be very worrying for parents.

When to seek medical advice

Contact your doctor or midwife if your child has the later symptoms of bronchiolitis described above. This is particularly important if your baby is under 12 weeks old or they have an underlying health problem, such as a congenital heart or lung condition. Congenital means that the condition is present from birth.

In all cases, be aware of any changes to your child’s symptoms. Contact your doctor again if you are worried or if your child develops any of the following symptoms:

• increased difficulty breathing or wheezing as they breathe
• poor feeding (if your child has taken less than half the amount that they usually do during the last two or three feeds)
• no wet nappy for 12 hours or more
• a rapid breathing rate of more than 40 breaths a minute
• a high temperature (fever) of 38C (100.4F) or above
• being very tired or irritable

When to call emergency services  

While it is unusual for children to need hospital treatment for bronchiolitis, the symptoms can get worse very quickly. Call emergency services for an ambulance if:

• Your child has severe breathing difficulties or exhaustion from trying to breathe. You may see the muscles under your child’s ribs sucking in with each breath, your child may be grunting with the effort of trying to breathe, or they may be pale and sweaty.
• Your child has a rapid breathing rate of more than 60 breaths a minute.
• You are unable to rouse (wake) your child or, if roused, they do not stay awake. 
• Your child’s breathing stops for more than 10 seconds at a time (this is known as recurrent apnoea).
• Your child’s skin begins to turn ashen (very pale) or blue, particularly around the lips or fingernails (known as cyanosis).

Causes of bronchiolitis 

Bronchiolitis is almost always caused by a viral infection. In 75% of cases, the virus responsible is the respiratory syncytial virus (RSV).

Respiratory syncytial virus (RSV)

RSV is a very common virus. Almost all children are infected with RSV by the time they are two years old. In older children and adults, RSV may cause a cough or cold, but in young children it can cause bronchiolitis.

Other viruses that may cause bronchiolitis include:

• parainfluenza virus
• influenza (flu) virus
• adenovirus
• rhinovirus

Catching a virus

Viruses are spread through tiny droplets of liquid from the coughs or sneezes of someone who is infected. The droplets can be breathed in directly from the air or picked up from a surface that they have landed on, such as a toy or table.

For example, your child can become infected if they touch a toy that has the virus on it and then touch their eyes, mouth or nose. RSV can survive on a surface for 6-12 hours.

Children can be infectious for up to three weeks after having the condition, even after their infection has cleared up.

The respiratory system

Once the virus has been caught, it enters the respiratory system through the windpipe (trachea). The virus makes its way down to the smallest airways in the lungs (the bronchioles).

The infection causes the bronchioles to become inflamed (swollen) and increases the production of mucus. The mucus and swollen bronchioles can block the airways, making it difficult to breathe. As babies and young children have small, underdeveloped airways, they are more likely to get bronchiolitis.

Risk factors

Bronchiolitis is very common in infants and is usually mild. However, some risk factors can make bronchiolitis more serious. These include:

• being under 12 months of age
• having congenital heart disease (a birth defect that affects the heart)
• being born prematurely (before week 37 of pregnancy)
• having chronic lung disease of prematurity (when injury to the lungs causes long-term respiratory problems in premature babies)
• being breastfed for less than two months or not at all
• being exposed to smoke, for example if parents smoke

having brothers or sisters who attend school or nursery (as they are more likely to come into contact a virus and pass it on)

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