What infection does Human Metapneumovirus (HMPV) cause?

Human Metapneumovirus (HMPV) Infections

Human metapneumovirus (HMPV) primarily causes acute respiratory tract disease in people of all ages, ranging from upper respiratory tract infections to severe pneumonia, with bronchiolitis being a common presentation in infants and young children. 1

Clinical Manifestations

HMPV infections can present with various clinical syndromes:

• Upper respiratory tract infections:

  • Common cold-like symptoms
  • Rhinorrhea (runny nose)
  • Congestion
  • Sore throat
  • Cough
  • Fever

• Lower respiratory tract infections:

  • Bronchiolitis (particularly in infants)
  • Pneumonia
  • Tracheobronchitis
  • Croup

• Exacerbations of underlying conditions:

  • Asthma exacerbations
  • COPD exacerbations
  • Otitis media (especially in children) 1, 2

Epidemiology and Risk Factors

• HMPV is responsible for approximately 5-10% of hospitalizations for acute respiratory tract infections in children 3
• Initial infection typically occurs during early childhood, but reinfections are common throughout life 3
• Seasonal circulation predominantly in winter months 1
• Higher risk populations include:
  • Young children (especially under 5 years)
  • Elderly individuals
  • Immunocompromised patients (particularly hematopoietic stem cell transplant recipients)
  • Patients with underlying cardiopulmonary disease 2, 4

Diagnosis

HMPV is primarily diagnosed through:

• Nucleic acid amplification tests (NAATs): The preferred diagnostic method due to the virus's slow growth in culture 1, 3
• Specimens of choice include:
  • Respiratory secretions
  • Nasopharyngeal swabs placed in viral transport medium 1
• Other diagnostic methods include:
  • Immunofluorescent assays
  • Commercial respiratory panels that include HMPV 1

Clinical Course and Complications

• Most cases present with mild to moderate symptoms 1
• In immunocompromised patients:
  • Prolonged viral shedding (potentially for weeks)
  • Higher risk of progression to lower respiratory tract infection
  • Potential for severe disease and fatal outcomes 1, 2
• Coinfections with other pathogens (bacterial, fungal, or viral) are common in severe cases 1
• Complications include:
  • Progression to pneumonia
  • Respiratory failure
  • ARDS in severe cases 2

Treatment

Treatment is primarily supportive as there are no approved specific antiviral therapies for HMPV:

• Supportive care:

  • Hydration
  • Antipyretics for fever
  • Oxygen supplementation as needed 2

• For severe cases:

  • Low tidal-volume mechanical ventilation for ARDS
  • Conservative fluid management
  • Consider ECMO for refractory hypoxemia 2

• Antibiotics should only be considered if bacterial superinfection is suspected 2

• Ribavirin and/or IVIG may be considered in severe cases in immunocompromised patients, though evidence is limited 1

Prevention and Infection Control

• Standard precautions:

  • Hand hygiene with alcohol-based hand gels
  • Respiratory/cough etiquette
  • Isolation of infected individuals 2

• Extended isolation for immunocompromised patients due to prolonged viral shedding 2

• No approved vaccines are currently available, though several candidates are in development 5, 6

Key Clinical Considerations

• HMPV symptoms often overlap with other respiratory viruses like RSV, making specific testing important for diagnosis 6
• Asymptomatic shedding can occur, especially in immunocompromised patients 1
• Viral load may correlate with symptom severity 1
• Close monitoring is essential for high-risk patients, particularly those who are immunocompromised 2

HMPV represents an important respiratory pathogen that should be considered in the differential diagnosis of respiratory infections, especially during winter months and in vulnerable populations.