Viral-induced wheeze occurs when a viral infection causes airway narrowing, leading to shortness of breath and wheeze. It is very common and typically affects children under 3 years of age. Children with viral-induced wheeze are more likely to develop asthma.
Viral-induced wheeze only occurs during viral infections. Viral infections can also trigger symptoms of asthma. However, the symptoms of asthma can be triggered by other factors, such as exercise, cold weather, dust and strong emotions.
Pathophysiology
Small children have small airways. Viral infections, commonly RSV or rhinovirus, can cause airway inflammation and oedema, narrowing the diameter and restricting air flow. The inflammation triggers the smooth muscles of the airways to constrict, further narrowing the space for air to flow.
Airway narrowing caused by a viral infection has little noticeable effect on the larger airways of an older child or adult. However, due to the small diameter of a child’s airway, minimal narrowing leads to a proportionally larger restriction in airflow. Airflow obstruction causes shortness of breath and wheeze.
Presentation
Patients will have evidence of a viral illness, such as:
- Low-grade fever
- Dry cough
- Coryzal symptoms (runny nose, sneezing and sore throat)
Typically, the viral symptoms are present for 1-2 days before the onset of:
- Shortness of breath
- Signs of respiratory distress (e.g., raised respiratory rate, accessory muscle use and recessions)
- Widespread expiratory wheeze on auscultation
TOM TIP: Neither viral-induced wheeze nor asthma causes a focal wheeze. If you hear a focal wheeze, be very cautious and investigate further for focal airway obstruction, such as an inhaled foreign body or tumour. These patients require an urgent senior review.
Management
Management is similar to an acute exacerbation of asthma, and may involve:
- Bronchodilators (e.g., inhaled salbutamol)
- Steroids (e.g., oral prednisolone for 3 days)
- Supplementary oxygen (if oxygen saturation is less than 94%)
Salbutamol inhalers are given via a spacer. High doses are used initially and gradually stepped down as tolerated, reducing the dose and increasing the space between doses. For example:
- 10 puffs every 2 hours
- 10 puffs every 4 hours
- 6 puffs every 4 hours
- 4 puffs every 6 hours
Last updated January 2025
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