Parainfluenza
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Background
Parainfluenza viruses (PIVs) are spherical, enveloped, single-stranded RNA paramyxoviruses transmitted via respiratory droplets and direct contact. They are a leading cause of respiratory infections in young children.There are 4 main serotypes - PIV-1. PIV-2, PIV
Epidemiology
- Seasonality: Infections peak in late autumn and winter for most strains
- Age group: Most common in children aged 6 months to 3 years, but can affect all ages.
- Antigenic variation: Unlike influenza viruses, PIVs do not undergo significant antigenic shift, so epidemics occur but pandemics do not.
Clinical Features
PIV infections range from mild upper respiratory tract infections (URTIs) to severe lower respiratory tract infections (LRTIs).
Common symptoms:
- Fever
- Coryza
- Hoarseness
- Sore throat
- Poor feeding
- Barking cough (typically worse at night)
- Inspiratory stridor and respiratory distress in severe cases.
Croup is the most common clinical manifestation in children, presenting with a harsh cough, stridor, and hoarseness.
Other possible presentations include
- Bronchiolitis (common with PIV-3 infection)
- Pneumonia (especially immunocompromised patients)
- Epiglottitis (rare)
Symptoms usually start to resolve within 48 hours
Other possible presentations include
- Bronchiolitis (common with PIV-3 infection)
- Pneumonia (especially immunocompromised patients)
- Epiglottitis (rare)
Symptoms usually start to resolve within 48 hours
Complications
While most cases are self-limiting, severe disease can lead to:- Respiratory distress
- Hypoxia requiring hospital admission
- Secondary bacterial infections e.g., pneumonia or otitis media
- Exacerbation of pre-existing conditions e.g., asthma
Diagnosis
Clinical diagnosis is often sufficient, particularly in children presenting with classical croup features.
Laboratory confirmation may be needed in severe cases or immunocompromised patients and may be identified via one of the following methods:
- Nasopharyngeal swabs
- NAAT or PCR) testing
- Direct immunofluorescence for rapid detection
- Viral culture (rarely used due to slow turnaround time)
Management
Treatment is typically supportive. Antiviral therapy is NOT routinely used for PIV. Oxygen therapy and steroids (oral dexamethasone 0.15 mg/kg OR nebulised budesonide 2 mg as a single dose) are often reserved for moderate to severe cases. For severe croup not effectively controlled with corticosteroid treatment, nebulised adrenaline/epinephrine solution 1 in 1000 (1 mg/mL) should be given with close clinical monitoring
Hospital admission criteria include:
- Moderate or severe illness, or impending respiratory failure.
- Respiratory rate of over 60 breaths/minute
- Child with high fever or 'toxic' appearance
- Child with mild illness but in at risk group eg. congenital heart disease, immunosuppressed etc
- Progressive respiratory distress
- Poor oral intake leading to dehydration
- Persistent hypoxia or cyanosis
- Suspected bacterial superinfection
Classification of croup
| Severity | Description |
|---|---|
| Mild | seal-like barking cough but no stridor or sternal/intercostal recession at rest |
| Moderate | seal-like barking cough with stridor and sternal recession at rest; no (or little) agitation or lethargy |
| Severe | seal-like barking cough with stridor and sternal/intercostal recession associated with agitation or lethargy |
| Impending respiratory failure | minimal barking cough, stridor may become harder to hear. Increasing upper airway obstruction, sternal/intercostal recession, asynchronous chest wall and abdominal movement, fatigue, pallor or cyanosis, decreased level of consciousness or tachycardia. The degree of chest wall recession may diminish with the onset of respiratory failure as the child tires. A respiratory rate of over 70 breaths/minute is also indicative of severe respiratory distress |
Prevention
No vaccine is availableGood hand and hygiene practices may reduce transmission.
Key Points
- Parainfluenza is the most common cause of croup accounting for approximately 80% of cases in the UK.
- Peaks are usually seen in the winter in the under 3 age group
- Epiglottitis is one complication as are bronchiolitis and pneumonia.
- Incubation varies from strain to strain but is in the 1-7 day range.
- Illness typically lasts 2-5 days
- There is currently no vaccine licensed for Parainfluenza virus in the UK.