Human Metapneumovirus (HMPV): Clinical Overview
Clinical Presentation
HMPV typically presents as upper respiratory tract infection with flu-like symptoms including rhinorrhea, nasal congestion, cough, and fever, but can progress to severe lower respiratory tract disease particularly in immunocompromised patients. 1
Immunocompetent Patients
- Upper respiratory symptoms include rhinorrhea, nasal congestion, cough, fever, fatigue, expectoration, diarrhea, and headache 1
- Symptoms are clinically indistinguishable from RSV infection 2
- Most infections are mild and self-limiting in healthy adults 3
Pediatric Populations
- Progression may include dyspnea, cyanosis, malaise, restlessness, poor feeding, and reduced activity 1
- Severe cases can evolve to respiratory failure unresponsive to conventional oxygen therapy, septic shock, metabolic acidosis, and coagulation dysfunction 1
- HMPV accounts for 5-10% of pediatric hospitalizations for acute respiratory infections 4, 2
High-Risk Immunocompromised Patients
- Symptomatic HMPV occurs in 2.5-9% of allogeneic HSCT recipients within the first two years post-transplant 5, 4
- Mortality ranges from 10-30% in HSCT patients who develop lower respiratory tract disease 4, 1
- Asymptomatic and prolonged viral shedding is common in HSCT patients, complicating infection control 5, 6
- Coinfection with other pathogens (bacteria, fungi, RSV, CMV) is frequent, obscuring attributable morbidity 5, 1
- Risk factors include cytomegalovirus seropositivity, higher corticosteroid exposure, neutropenia, and lymphopenia 5, 6
Critical Pitfall
No clinical or radiographic criteria reliably distinguish HMPV from bacterial infection, necessitating a low threshold for empirical antibiotics in severe cases 1
Diagnostic Methods
Reverse transcription-polymerase chain reaction (RT-PCR) is the preferred diagnostic method for HMPV, as the virus is difficult to culture in vitro. 7, 2
Recommended Approach
- Nucleic acid amplification testing (NAT) is the standard diagnostic modality, often performed in multiplex formats 5
- RT-PCR is preferred over viral culture due to slow growth characteristics of HMPV in cell culture 7, 8
- Testing should be performed on respiratory specimens (nasopharyngeal swabs, bronchoalveolar lavage in severe cases) 5
Epidemiologic Context
- Incubation period is 3-5 days (some sources report 2.6 days), facilitating nosocomial outbreaks 4, 6
- Peak incidence occurs during winter and spring months 7, 9
- Nearly all children are infected by age 5, with re-infections common throughout life due to incomplete immunity 8, 3
Management Recommendations
Immunocompetent Adults
Supportive care only is recommended for immunocompetent adults with HMPV infection, as no antiviral agent has established efficacy. 6, 1
- Rest, hydration, and symptomatic management are the mainstays of therapy 6
- Oxygen therapy titrated to maintain adequate saturation 6
- Monitoring of vital signs, oxygen saturation, and respiratory status 6
- Fluid and electrolyte management 6
- Treatment of bacterial superinfection if suspected or documented 6
Immunocompromised Patients with Lower Respiratory Tract Disease
Consider treating HMPV lower respiratory tract disease with ribavirin and/or intravenous immunoglobulin in immunocompromised patients, despite the lack of randomized controlled trial data supporting this approach. 5, 6
Treatment Algorithm for HSCT Recipients and Leukemia Patients:
- Upper respiratory tract infection alone does not typically warrant antiviral therapy 6
- Lower respiratory tract involvement (pneumonia, bronchiolitis) warrants consideration of ribavirin and/or IVIG, particularly in:
Important Caveats:
- No general recommendation for treatment can currently be made based on available evidence 5, 6
- Some centers use ribavirin and/or IVIG for LRTID despite lack of supporting studies 5
- Single cases of severe disease and fatal outcomes have been reported even with treatment attempts 6
Severe Disease Management
- High-flow nasal oxygen (HFNO) or non-invasive ventilation (NIV) as initial escalation for moderate to severe ARDS 6
- Invasive mechanical ventilation with prone positioning for severe ARDS 6
- High-protein, high-vitamin, carbohydrate-containing diets for nutritional support 6
Infection Control
Implement standard and droplet precautions to prevent nosocomial transmission, given the high rates of asymptomatic shedding and short incubation period. 6
- Asymptomatic shedding rates may be substantial (up to 41% in some HSCT populations), highlighting the need for rigorous infection control 6
- Prolonged viral shedding has been documented in HSCT patients 6
- Nosocomial outbreaks can occur given the estimated incubation period of 2.6-5 days and high rates of asymptomatic shedding 4, 6
- Transmission occurs through droplet or aerosol contamination 9