What are the clinical presentation, diagnostic approach, and management options for human metapneumovirus infection, particularly in high‑risk or immunocompromised patients?

Human Metapneumovirus (hMPV) Infection

Clinical Presentation

hMPV causes respiratory tract infections ranging from mild upper respiratory symptoms to severe pneumonia, with clinical features indistinguishable from RSV and other respiratory viruses. 1, 2

Typical Symptoms

• Upper respiratory manifestations include rhinorrhea, nasal congestion, cough, fever, sore throat, and sneezing 1, 2
• Additional symptoms encompass fatigue, expectoration, diarrhea, and headache, particularly in pediatric patients 2
• Severe cases may progress to dyspnea, cyanosis, malaise, restlessness, poor feeding, reduced activity, and respiratory failure unresponsive to conventional oxygen therapy 2

High-Risk Populations

• Children under 5 years old, elderly patients, and immunocompromised individuals (particularly hematopoietic stem cell transplant recipients) face the highest risk of severe disease 1, 2, 3
• Patients with chronic cardiac or pulmonary diseases have substantially elevated mortality risk 2
• In HSCT recipients, symptomatic hMPV occurs in 2.5%–9% within the first two years post-transplant, with mortality ranging from 10% to 30% when lower respiratory tract disease develops 4, 2

Key Clinical Pitfalls

• No clinical or radiographic criteria reliably distinguish hMPV from bacterial infection, necessitating empirical antibiotics in severe cases 2
• Coinfection with other respiratory pathogens (especially RSV, bacteria, fungi) is common and obscures attributable morbidity 1, 4, 2
• Asymptomatic and prolonged viral shedding occurs frequently in immunocompromised patients, complicating diagnosis and infection control 4, 5, 2

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Diagnostic Approach

Nucleic acid amplification testing (NAAT) of respiratory specimens is the preferred diagnostic method, as hMPV grows slowly and fastidiously in culture. 1, 3, 6

Specimen Collection

• Nasopharyngeal swabs or respiratory secretions placed in viral transport medium are the specimens of choice, transported at room temperature within 2 hours 1
• In immunocompromised adults, lower respiratory tract specimens (BAL, endotracheal aspirate) are significantly more sensitive than upper respiratory specimens 1
• For HSCT recipients, discordance rates between upper and lower respiratory specimens reach 44% for hMPV, compared to only 8% for RSV 1

Testing Modalities

• Multiplex PCR respiratory panels are now widely available commercially and detect hMPV along with other respiratory viruses 1
• Immunofluorescent assays are available but less sensitive than molecular methods 1
• Culture is not recommended due to slow growth (4–7 days) and poor sensitivity 3, 6

When to Test

• The American Thoracic Society recommends considering nucleic acid-based testing for noninfluenza viral pathogens in immunocompromised patients at high risk for death from respiratory viral infection 1
• Testing is particularly important in HSCT recipients, lung transplant recipients, and patients with severe immunosuppression 1
• Upper respiratory testing alone may be insufficient to exclude lower tract infection in critically ill and immunocompromised patients 1

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Management

Supportive care is the mainstay of treatment for immunocompetent patients, while immunocompromised patients with lower respiratory tract disease may be considered for ribavirin and/or intravenous immunoglobulin despite limited evidence. 5

Immunocompetent Patients

• The Infectious Diseases Society of America and American College of Physicians recommend rest, hydration, and symptomatic management only 5
• Oxygen therapy should be titrated to maintain adequate saturation, with monitoring of vital signs and respiratory status 5
• Fluid and electrolyte management is essential 5
• Treat bacterial superinfection if suspected or documented 5

Immunocompromised Patients

• The CDC considers treating hMPV lower respiratory tract disease with ribavirin (oral or aerosolized) and/or intravenous immunoglobulin in immunocompromised patients, particularly HSCT recipients and leukemia patients with pneumonia 5, 7
• Upper respiratory tract infection alone does not typically warrant antiviral therapy 5
• Risk factors for severe disease include higher corticosteroid exposure, neutropenia, and lymphopenia 5
• For moderate to severe ARDS, escalate to high-flow nasal oxygen or non-invasive ventilation initially, with invasive mechanical ventilation and prone positioning for severe ARDS 5

Critical Limitations

• No antiviral agent has established efficacy for hMPV treatment based on randomized controlled trial data 1, 5, 2
• The American Thoracic Society notes that effective antivirals for hMPV are not clinically available 1
• Ribavirin use is based solely on in vitro activity and observational data 1, 7
• No FDA-approved antivirals or vaccines exist for hMPV 1, 8

Infection Control

• Implement standard and droplet precautions to prevent nosocomial transmission, given the 3–5 day incubation period and high rates of asymptomatic shedding 4, 5
• Prolonged viral shedding in HSCT patients necessitates extended precautions 4, 5
• Nosocomial outbreaks can occur in healthcare settings due to short incubation and asymptomatic transmission 4

Nutritional Support

• Provide high-protein, high-vitamin, carbohydrate-containing diets for nutritional support 5