Viruses That Cause Croup
Parainfluenza viruses, particularly types 1 and 2, are the primary cause of croup (laryngotracheobronchitis), while other viruses including respiratory syncytial virus (RSV), influenza viruses, human metapneumovirus, rhinoviruses, adenoviruses, and coronaviruses can also cause this condition. 1, 2
Primary Viral Causes
- Parainfluenza viruses are the most common cause of croup, with types 1 and 2 specifically associated with the croup syndrome, accounting for the majority of cases 1, 2
- Parainfluenza virus infections are responsible for up to 11% of all hospitalizations in children under 5 years of age 1, 3
- Type 3 parainfluenza virus is more commonly associated with bronchiolitis and pneumonia rather than croup 1
Secondary Viral Causes
- Respiratory syncytial virus (RSV) can cause croup and is recognized as a substantial cause of respiratory illness in both children and adults 2, 4
- Human metapneumovirus has been associated with cases of croup in children, along with bronchiolitis, pneumonia, and exacerbations of asthma 1, 2
- Influenza viruses (types A and B) can cause croup, with influenza-associated croup often presenting with more severe symptoms than parainfluenza-associated croup 1, 2
- Human coronaviruses (229E, NL63, OC43, and HKU1) can cause croup in addition to their more common presentation as upper respiratory infections 1, 2
- Adenoviruses may cause croup, though they are less commonly implicated than parainfluenza viruses 1, 2
- Rhinoviruses, typically associated with the common cold, can occasionally cause croup 1, 2
Epidemiology and Clinical Significance
- Croup affects approximately 3% of children per year, most commonly between the ages of 6 months and 3 years 5
- About 75% of croup infections are caused by parainfluenza viruses 5, 6
- Most children with croup have mild symptoms that resolve within 48 hours 3, 5
- Only 1-8% of patients with croup require hospital admission, and less than 3% of hospitalized patients need intubation 3
- Croup can occur in older children and adolescents, though it is less common in these age groups 7
Clinical Presentation
- Croup typically begins with symptoms resembling an upper respiratory tract infection, including low-grade fever and rhinorrhea 3
- These initial symptoms are followed by the characteristic barking cough and varying degrees of respiratory distress 3, 4
- Stridor, hoarseness, and respiratory distress due to upper airway obstruction are hallmark features 5, 6
- Symptoms often worsen at night and improve during the day 5
Diagnostic Considerations
- The diagnosis of croup is primarily clinical, based on the characteristic barking cough and associated symptoms 4, 6
- When evaluating a child with suspected croup, other diagnoses to consider include bacterial tracheitis, epiglottitis, foreign body aspiration, and angioedema 3, 2
- Recurrent croup (defined as two or more episodes per year) should prompt investigation for underlying structural or inflammatory airway abnormalities 8