Human metapneumovirus (hMPV) is a respiratory virus found in both clinical and community settings. Research on serological evidence demonstrated that hMPV has periodically been infecting the human population since the 1950s, but the existence of hMPV was only confirmed in 2001. The Pneumoviridae family comprises two genera: Metapneumovirus, which includes hMPV and the subfamily Orthopneumovirinae includes Respiratory syncytial virus (RSV). This classification emphasizes the connection among these viruses but different clinical and epidemiologic characteristics.
hMPV shares similar genetic and clinical characteristics with other respiratory viruses, which continues to pose a diagnostic challenge. Research indicates that testing rates for hMPV are low, even in routine clinical settings, contributing to its under-recognition in both research and clinical practice. Testing identifies a broad range of respiratory ailments involving the flu, severe lower respiratory ailments like asthma, pneumonia, and bronchitis together with hMPV. The history of high incidence rates of severe hMPV infections in children and high-risk adults is apparent. Collected data on severe cases, however, still lack in adults. One study shows that 11% of hospitalized hMPVs require ventilatory support, and approximately 12% of hMPV cases require ICU admission.Â
According to the 2024 PERCH study (Pneumonia etiology research for child health), which was carried out in Asia and Africa, hMPV is the second most prevalent severe cause of pneumonia in children under five years of age, behind RSV. Additionally, the study found that it is more frequently linked to bacterial infections, which raises the risk of morbidity and death in children who have pneumonia.
A 68-year-old man presented with a history of mild arterial hypertension, dyslipidemia, and long-term aspirin use presented with progressively worsening respiratory symptoms was an active man with no significant comorbidities, but he complained of intermittent dry cough (D1). Over the next few days, additional symptoms such as allodynia, nasal congestion, and nocturnal sweating (D2) began to develop. There was no response to empirical antibiotic and steroid treatment, and a nasopharyngeal swab for SARS-CoV-2 on (D2) was negative. On (D3), empirical therapy with amoxicillin-clavulanate, clarithromycin, and oral prednisone was initiated (D4); however, the patient’s condition worsened. By D5, he experienced bronchospasm and intense coughing, followed by a productive cough with thick, yellow-brown sputum, along with fatigue, headache, and myalgia.
The patient was admitted to the emergency department on the seventh day with SpOâ‚‚ range between 91% and 92%, increased inflammatory markers, blood pressure (BP) reported 140/80 mmHg, C-reactive protein (CRP) level of 7.6 mg/dL and a D-dimer 870 ng/mL. Molecular testing via multiplex Reverse transcription polymerase chain reaction (RT-PCR) for hMPV was positive.Â
Coinfection was ruled out for other bacteria and viruses. The findings were consistent with a diagnosis of viral pneumonia without bacterial superinfection.
Making a diagnosis of hMPV is difficult, especially because the clinical characteristics are like those of other respiratory viruses. New emerging methods such as multiplex RT-PCR have improved the identification of disease-causing organisms with high sensitivity and specificity as presented in this study. Nevertheless, low rates of testing and dependence on empirical therapy are still a major impediment.
Further investigations in the emergency department were performed with molecular testing by multiplex RT-PCR panel. These tests showed hMPV to be the only etiologic agent, although bacterial, atypical, and other viral co-factors were not identified. SARS-CoV-2 was also ruled out using qualitative immunochromatographic antibody testing. Molecular testing provides rapid and accurate results within approximately one hour, enabling a more appropriate clinical approach for managing and establishing the viral etiology.
Laboratory tests revealed evidence of a viral etiology, as procalcitonin levels were normal at 0.054 ng/mL. Other significant findings included elevated inflammatory markers, with CRP at 7.6 mg/dL and D-dimer at 870 ng/mL. Liver enzymes showed slightly elevated AST at 45 U/L and ALT at 39 U/L. Mildly elevated renal function markers were noted, with creatinine at 1.47 mg/dL and urea at 41 mg/dL, suggesting some systemic involvement. These results, combined with clinical and imaging findings, provided the diagnosis of viral pneumonia due to hMPV.
The transmission of hMPV occurs through respiratory droplets, contact with the infected surfaces, and direct contact; hence, proper infection control measures are required. However, there are no FDA-approved antivirals or vaccines for hMPV, and the gap in respiratory care is starkly evident. Promising vaccine developments include RNA-based platforms and bivalent candidates such as IVX-A12 (hMPV and RSV, phase II).Â
Continued investment in vaccine development is crucial to reducing the global burden of these infections. Molecular diagnostics should be utilized even more often in daily clinical practice because they contribute to the improvement of patients’ conditions during the spread of seasonal respiratory viruses.
This case highlights the growing clinical awareness of hMPV in various populations, particularly during the season of respiratory virus outbreaks. The burden of hMPV-associated pneumonia has brought attention to the need for more funding in diagnostics, new therapies, and improved access to care. Further research and targeted public health initiatives are essential to address the morbidity and mortality caused by this emerging pathogen.
References: Costa-Filho RC, Saddy F, Costa JLF, Tavares LR, Castro Faria Neto HC. The Silent Threat of Human Metapneumovirus: Clinical Challenges and Diagnostic Insights from a Severe Pneumonia Case. Microorganisms. 2025; 13(1):73. doi:10.3390/microorganisms13010073
