Parainfluenza

Background

• An enveloped, negative-sense, single-stranded RNA virus
  • Related to but of a different family classification as the influenza virus.
  • There are 4 known serotypes.
• Capable of causing both upper and lower airway disease
  • Most commonly known as a causative agent of croup (laryngotracheobronchitis).

High Risk Groups

• Young children (<5 years old)
  • Relatively narrow airway passages
• Immunocompromised
• Underlying chronic cardiac or respiratory conditions

Clinical Features

Can result in a large number of varied presentations

Pediatric Patients

• Croup: Peak age is 1-2 years, with boys slightly more likely to present than girls. Infection begins in upper airway but often lower airway signs (wheezing, air trapping)
• Bronchiolitis: Causative agent in 10-20% of diagnosed bronchiolitis. Initially fever and congestion for 1-3 days followed by lower airway symptoms, including cough and wheezing. Most recover within 21 days, though children with underlying pulmonary conditions are a risk of prolonged course and greater complications
• Pneumonia: Indistinct from other presentations of viral pneumonia with a similar overall disease course as bronchiolitis.
• Tracheobronchitis: Inflammation of only the large airways in the absence of evidence of croup or pneumonia.

Up to half of the above are complicated by concurrent otitis media

Adult Patients (Immunocompetent)

• Generally mild URI cold symptoms, though can also initiate exacerbation of COPD, asthma, or CHF

Adult Patients (Immunocompromised)

• Often initially URI cold symptoms but high risk to progress to pneumonia

Differential Diagnosis

Pediatric Patients

• Foreign object airway obstruction
• Other viral infection (including RSV, influenza virus, adenovirus, rhinovirus, COVID)
• Bacterial respiratory infection

Adult Patients

• COPD exacerbation
• Asthma exacerbation
• Other viral infection
• Bacterial respiratory infection

Influenza-Like Illness

• Influenza
• Parainfluenza
• URI
• Pneumonia
• Sinusitis
• Toxic exposure
• Pyelonephritis
• Bronchitis
• Coronavirus
  • MERS-CoV
  • SARS-CoV
  • 2019-nCoV (COVID-19)

Evaluation

Workup

• Chest X-ray
  • Often helpful in confirming diagnosis of a viral syndrome,
  • The canonic "steeple sign" is not a unique finding to parainfluenza infection.
• In the absence of signs of dehydration or other concurrent conditions (immunocompromised, COPD exacerbation, asthma exacerbation, CHF exacerbation), additional workup is not typically needed.

Diagnosis

• Presentation shares many characteristics with other viruses, including RSV and influenza virus. It must also be distinguished from bacterial causes of upper and lower respiratory infections. In general, in the absence of warning signs it is not especially important to specifically diagnose a parainfluenza virus infection.
• In the emergency department context, PCR assays are the most likely confirmatory testing to yield results in a reasonable timeframe.

Management

• Assure airway stability
  • Any signs of airway compromise should be addressed aggressively up to and including intubation.
  • While wheezing is often a hallmark, as with other airway conditions the absence of wheezing may suggest significant airway obstruction and should not necessarily be viewed as a reassuring sign.
• Symptomatic management
  • See croup for treatment of that entity
• There are not currently any antiviral agents available for treatment

Disposition

• Generally, pediatric patients without signs of respiratory distress may be discharged and managed symptomatically in the outpatient setting.
• Immunocompromised adults and those with concurrent COPD exacerbation, asthma exacerbation, or CHF exacerbation typically require admission for monitoring and management of symptoms.

See Also

• Croup