An acute, infectious disease of the lower respiratory tract that occurs, predominantly, in infants between 2 and 6 months old.


  • Most commonly viral infection
    • Usually respiratory syncytial virus (RSV- 75%) but also human metapneumovirus (hMPV), adenovirus and parainfluenza virus
    • Around 70% of all babies will be infected with RSV in the first year of life
      • Around 22% develop symptomatic disease
    • Around a third of all infants will develop a bronchiolitis at some point
  • One of the biggest causes of infants under one year requiring admission to hospital (around 3% of all infants)- however the majority stay for 1 day
  • Peak incidence in the winter months
  • Risk factors include: older siblings, nursery attendance, passive smoking, overcrowding
    • Risk factors for worse disease include prematurity & low birth weight, <12 weeks old, cardiac problems, respiratory problems (CF), Down’s syndrome
    • Breast feeding is protective


  • Coryzal symptoms may be present prior to the onset of severe symptoms
    • e.g. rhinorrhea, cough, mild fever
      • NB high fever >39°C is uncommon and should prompt investigation into other causes.  Similarly, the absence of fever does not exclude bronchiolitisl
      • Cough is usually dry and wheezy
  • Other symptoms include problems with feeding, trouble breathing, vomiting irritability
    • Apnoea may also occur, particularly in young infants
  • Signs include tachypnoea, tachycardia, respiratory distress (increased work of breathing- using accessory muscles)
    • Upon auscultation of the lungs, widespread fine inspiratory crackles
      • (In the US, more emphasis is put on the presence of an expiratory wheeze)
    • It is unusual for the patient to appear ‘toxic’- i.e. lethargic/irritable – if so, this requires more urgent management for an underlying cause as these patients may dramatically decline
    • Cyanosis is not common but can be a feature


  • Most investigations are not warranted if a clinical diagnosis is clear
  • Viral swabs from nasopharynx are perhaps the only investigation (other than O2 sats) that will be necessary
  • Other tests e.g. blood investigations, CXR- are only required if a patient should deteriorate to more severe illness


  • Most cases are mild and self-limiting and can be managed at home.
  • Patients requiring referral:
    • Poor feeding (<50% of usual intake in 24 hours, or inadequate to maintain hydration)
    • Lethargy
    • History of apnoea
    • Respiratory rate >70bpm
    • Nasal flaring/grunting
    • Severe chest wall recession
    • Cyanosis
    • Saturations <94%
      • NB Threshold for referring should be low in patients with significant comorbidity/premature/young children (<12 weeks)

2 thoughts on “Bronchiolitis”

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: