Human Metapneumovirus: Clinical Manifestations in Adults and Pediatric Patients
Human metapneumovirus (HMPV) causes respiratory tract infections ranging from mild upper respiratory symptoms to severe pneumonia and bronchiolitis, with clinical presentation varying significantly by age and immune status. 1, 2
Pediatric Patients
Common Presentations
- Bronchiolitis and pneumonia are the predominant manifestations in infants and young children, accounting for approximately 10% of hospitalizations for acute respiratory infections 2, 3
- Upper respiratory symptoms include rhinorrhea, nasal congestion, cough, and fever 1, 4
- Children may present with mild to moderate symptoms in most cases, though severe disease requiring hospitalization occurs particularly in infants 0-5 months old 3
- Additional symptoms include fatigue, expectoration, diarrhea, and headache 1
High-Risk Features in Children
- Infants under 5 months are at highest risk for severe disease 3
- Significant respiratory distress often necessitates hospitalization 2
- Symptoms can progress to include dyspnea, cyanosis, malaise, restlessness, poor feeding, and reduced activity 1
- In severe cases, progression to respiratory failure unresponsive to conventional oxygen therapy, septic shock, metabolic acidosis, and coagulation dysfunction may occur 1
Adult Patients
Typical Clinical Features
- Dyspnea (86%) and cough (85%) are the most frequent symptoms in hospitalized adults 5
- Symptoms often mimic influenza and can exacerbate chronic conditions like COPD or asthma 2, 3
- The median time from symptom onset to hospital admission is 3 days (range 2-7 days) 5
- Incubation period is estimated at 3-6 days, with most cases lasting 2-5 days before resolving 4
Common Diagnoses
- Pneumonia (42%) is the most frequent clinical diagnosis in hospitalized adults 5
- Acute bronchitis (20%) and acute exacerbation of COPD (16%) are also common presentations 5
- Ground glass opacities on CT scan are the most frequent radiographic finding (41% of patients who underwent imaging) 5
High-Risk Adult Populations
- Elderly patients (median age 74 years in hospitalized cohorts) are particularly vulnerable 5
- Adults over 65 years face increased risk of severe disease and mortality 3
- 90% of hospitalized adults have at least one coexisting illness 5
- Immunocompromised patients (31% of hospitalized cases) experience more severe disease 5
- Patients with chronic cardiac or pulmonary diseases are at elevated risk 1
Severe Disease and Complications
Critical Outcomes
- Complicated course (death and/or need for invasive mechanical ventilation) occurs in approximately 18% of hospitalized adults 5
- ICU admission is required in 29% of hospitalized adults, with 38% of ICU patients requiring invasive mechanical ventilation 5
- Tachycardia and altered consciousness are independent risk factors for complicated course 5
Bacterial Coinfection
- Bacterial coinfection occurs in 29% of hospitalized adults with HMPV 5
- Mixed flora (16%) and enterobacteria (5%) are the predominant bacterial pathogens 5
- Among pneumonia patients, bacterial coinfection significantly increases the risk of complicated course (33% vs 8% without coinfection) 5
- Despite this, over 80% of patients receive empirical antibiotic therapy 5
Key Clinical Pitfalls
Diagnostic Challenges
- No clinical or radiographic criteria reliably distinguish HMPV from bacterial infection, necessitating a low threshold for empirical antibiotics in severe cases 1
- Asymptomatic and prolonged viral shedding can occur, complicating infection control 1
- Coinfection with other respiratory viruses (especially RSV) is common and obscures attributable morbidity 1
Risk Stratification
- High viral load is associated with more severe disease 3
- The presence of comorbidities, particularly cardiopulmonary disease, substantially increases mortality risk 1
- In immunocompromised patients (including HSCT recipients), HMPV can cause severe LRTID with 10-30% mortality 1