When is testing for human metapneumovirus (hMPV) infection crucial?

When to Test for Human Metapneumovirus (hMPV) Infection

Testing for human metapneumovirus (hMPV) is primarily indicated in immunocompromised patients at high risk for death from respiratory viral infections, critically ill patients with suspected pneumonia, and in outbreak settings to guide infection control measures. 1

Priority Patient Populations for hMPV Testing

High-Risk Immunocompromised Patients

• Hematopoietic stem cell transplant recipients
• Solid organ transplant recipients (especially lung transplant)
• Oncology patients receiving chemotherapy
• Other severely immunocompromised individuals 1

Critical Care Settings

• ICU patients with new fever and suspected pneumonia
• Patients with severe respiratory symptoms requiring mechanical ventilation
• Cases of unexplained acute respiratory distress syndrome (ARDS) 1, 2

Special Considerations

• Pediatric patients with bronchiolitis, croup, or severe respiratory symptoms
• Outbreak investigations in healthcare facilities or institutional settings
• Patients with underlying cardiopulmonary disease 1

Clinical Scenarios Warranting Testing

1. Immunocompromised patients with respiratory symptoms

   • Testing is crucial as hMPV can cause severe disease and high mortality in this population
   • Prolonged viral shedding may occur, requiring extended isolation precautions 1, 3

2. Critically ill patients with pneumonia

   • When bacterial cultures are negative but respiratory symptoms persist
   • When determining appropriate isolation measures is necessary
   • To guide antimicrobial stewardship decisions 1

3. Outbreak management

   • To identify the causative pathogen in institutional outbreaks
   • To implement appropriate infection control measures
   • For epidemiological surveillance 3

Testing Methods and Specimen Collection

• Preferred method: Nucleic acid amplification tests (NAATs), typically as part of multiplex respiratory panels 1
• Specimen types:
  • Nasopharyngeal swabs/aspirates (most common)
  • Bronchoalveolar lavage fluid (for lower respiratory tract disease)
  • Endotracheal aspirates in intubated patients 1, 4
• Timing: Collect specimens as early as possible in the course of illness for optimal detection 1

Clinical Impact of Testing

• Treatment guidance: While no specific antivirals are approved for hMPV, testing can:

  • Avoid unnecessary antibiotics when a viral etiology is confirmed
  • Guide supportive care decisions
  • Identify patients who may require more intensive monitoring 3

• Infection control:

  • Implement appropriate isolation precautions
  • Prevent nosocomial spread, especially to vulnerable patients
  • Determine duration of isolation (particularly important for immunocompromised patients who may shed virus for extended periods) 3

Important Caveats and Pitfalls

• Testing for hMPV alone is rarely indicated; multiplex respiratory panels that include hMPV and other common respiratory viruses are typically more appropriate 1
• A positive test in immunocompromised patients may represent prolonged shedding rather than acute infection 1
• False negatives can occur if specimens are collected late in the course of illness 1
• Consider the cost-effectiveness of testing, as it may not alter management in mild cases in otherwise healthy adults 1

Bottom Line

Testing for hMPV should be targeted to high-risk populations where identification of the virus would impact clinical management, infection control practices, or patient outcomes. The highest yield and impact will be in immunocompromised patients, critically ill patients with suspected viral pneumonia, and during institutional outbreaks.