Acute Bronchiolitis

What happens in bronchiolitis

The virus infects the cells lining the bronchioles, the tiny airways that branch off into the air sacs. The lining swells, makes extra mucus, and dead cells slough into the airway. Because babies' airways are so narrow, even small amounts of swelling and mucus block airflow, causing wheezing, crackles and fast breathing. Babies also breathe mainly through the nose, so a blocked nose makes feeding hard.

Bronchiolitis occurs mostly in winter epidemics, though seasons have shifted in recent years. Almost all children have caught RSV by age 2, but only the first infections, at the youngest ages, tend to cause bronchiolitis.

Symptoms day by day

1. Days 1 to 2: runny nose, mild cough, sometimes a low fever.
2. Days 3 to 5: cough worsens, breathing becomes faster and harder, wheezing, feeding drops. This is when babies are most likely to need care.
3. After day 5: breathing gradually eases over the following days.
4. Weeks 2 to 4: a lingering cough is common and normal.

Young babies under 6 weeks may have apnea (pauses in breathing) as the first or only sign.

Signs of breathing difficulty to watch

• fast breathing (60 or more breaths a minute)
• skin pulling in between or under the ribs or at the base of the neck
• flaring nostrils
• grunting on breathing out
• head bobbing with each breath
• pauses in breathing

Who is at higher risk of severe illness

• babies under 3 months
• babies born before 37 weeks
• congenital heart disease or chronic lung disease
• weakened immune system or neuromuscular conditions
• Down syndrome
• exposure to tobacco smoke, and not being breastfed

Diagnosis

Doctors diagnose bronchiolitis from the history and exam: a cold followed by cough, fast breathing, crackles and wheeze in a child under 2. A pulse oximeter measures oxygen levels. Chest X-rays and blood tests are not routinely recommended because they rarely change treatment and can lead to unnecessary antibiotics. A nose swab may be used in hospital to identify RSV for infection control.

Treatment

There is no medicine that cures bronchiolitis. Treatment supports the baby while the infection runs its course.

At home

• Small, frequent feeds: offer breast milk or formula more often in smaller amounts.
• Clear the nose: saline drops followed by gentle suction with a bulb or nasal aspirator before feeds and sleep.
• Keep the baby upright for feeds. Always put babies to sleep on their back.
• Fever: acetaminophen (paracetamol) from 2 to 3 months, or ibuprofen from 6 months if the baby is drinking well. Follow the label dose for weight or age.
• Keep away from smoke.

In hospital

• Oxygen if saturation falls below about 90 to 92%.
• Fluids by a tube through the nose into the stomach, or intravenously, if the baby cannot feed.
• High-flow nasal oxygen or CPAP for babies who are tiring.
• A small number need intensive care and a ventilator.

What does not help

National guidelines advise against routine use of albuterol (salbutamol) inhalers, steroids, antibiotics, adrenaline nebulizers, and chest physiotherapy for typical bronchiolitis. Cough and cold medicines should not be given to babies.

Complications

• dehydration from poor feeding
• apnea in young infants
• respiratory failure needing ventilation (rare)
• secondary bacterial infection such as an ear infection, and rarely pneumonia
• recurrent wheezing in the following years. Severe RSV bronchiolitis is linked with later wheeze and childhood asthma, though whether it causes asthma is debated.

Prevention

• RSV antibody for infants: nirsevimab is a single injection given to babies entering their first RSV season and to some high-risk children in their second. Clesrovimab is a newer option. These significantly reduce RSV hospital admissions.
• Maternal RSV vaccine: given in late pregnancy (around 32 to 36 weeks in the US) during RSV season, it passes protective antibodies to the baby. Most babies need either the maternal vaccine or the infant antibody, not both.
• Palivizumab: monthly injections previously used for high-risk infants, now largely replaced.
• Everyday measures: hand washing, keeping young babies away from people with colds, no smoking around children, and breastfeeding.

Bronchiolitis vs other chest illnesses

Frequently asked questions

How long does acute bronchiolitis last?

Symptoms are usually worst on days 3 to 5 and then improve over a week or two. The cough often lasts 2 to 4 weeks. See a doctor if the cough lasts beyond 4 weeks or your baby gets worse after starting to improve.

Is bronchiolitis contagious?

Yes. The viruses that cause it spread through droplets and contaminated hands and surfaces. Children are most contagious in the first few days but can shed RSV for 1 to 3 weeks. Older children and adults usually get only a cold from the same virus.

What is the difference between bronchitis and bronchiolitis?

Bronchiolitis affects the smallest airways in babies and toddlers under 2, causing wheeze and breathing difficulty. Bronchitis affects the larger airways, mainly in older children and adults, causing a cough with mucus. Both are usually viral.

When should a baby with bronchiolitis go to hospital?

Go to hospital if your baby is struggling to breathe, has pauses in breathing, turns blue, is taking less than half of usual feeds, has no wet diaper in 12 hours, or is unusually sleepy. Babies under 3 months need a lower threshold for medical review.

Can bronchiolitis be prevented?

Yes, largely. A single RSV antibody injection for infants, or an RSV vaccine given in late pregnancy, sharply reduces severe RSV illness. Hand washing, avoiding smoke and keeping young babies away from people with colds also help.