The human metapneumovirus (hMPV) was first described in 2001. It belongs to the paramyxovirus family (paramyxoviridae subfamily). hMPV is genetically close to the Respiratory Syncytial Virus (RSV). hMPV has a seasonal epidemic pattern, between January to April. Incubation period varies between 4 and 6 days. Clinical symptoms of hMPV infection are close to that of RSV, with influenza-like illness (fever, asthenia and curvatures) associated with signs of upper and/or lower respiratory tracts infection. The incidence of hMPV infection is higher in children than in adults. In a large cohort of children with respiratory illness or fever, hMPV was detected in 7 % of outpatients and 6 % of hospitalized children. The annual rate of hospitalization associated with hMPV infection has been estimated about 1 per 1000 children less than 5 years of age. In child pneumonia, hMPV is the third most frequent isolated pathogen (14 % of the subjects), after rhinovirus and RSV. In hospitalized adults, hMPV was detect in 6 to 8% of the subjects with a lower respiratory tract and in 4 % of subjects with a pneumonia.

Clinical, radiological and biological features, as well as evolution course of hMPV-associated infections have been mainly described in children. Clinical presentation of hMPV-associated infection in adult seems polymorph, ranging from acute bronchitis or exacerbation of chronic pulmonary diseases (COPD and asthma) to pneumonia. Viral-viral coinfections are not exceptional whereas the frequency of viral-bacterial coinfection is unknown. Intensive care unit (ICU) admission involved almost 1 for 10 patients. Elderly and immunocompromised subjects are probably high-risk subjects. Only one cohort of hMPV-infected patients admitted to ICU has been reported. Among the 40 patients, 6 were non-immunocompromised and without comorbidity. Factors associated with a poor prognosis were not studied.

Currently, treatment of hMPV-associated lower respiratory tract infections is mainly symptomatic. However, several anti-RSV drugs that are currently in clinical development in humans, have demonstrated an activity against other paramyxoviridae (hMPV and parainfluenza virus) in pre-clinical studies. These anti-RSV drugs should be available for clinicians in the next few years. Considering their activity against other paramyxoviridae, clinicians will probably attempt to use these anti-RSV drugs in non-RSV paramyxoviridae-associated lower respiratory tracts infections in adult inpatients. Consequently, it seems necessary to better characterize hMPV-associated lower respiratory tracts infections in adult inpatients: clinical, radiological and biological presentation, course profile and risk factors for morbidity and mortality. These data would help clinicians to identify high risk patients, and consequently to choose those who could benefit from coming treatments.

The French hMPV Study is observational prospective multicenter clinical study. The study population includes all consecutive adult inpatients with a community-acquired acute lower respiratory tract infection and a mPCR positive for hMPV on any respiratory sample. The primary objective is to describe the prognosis. The secondary objectives are i) to characterize the clinical (time from onset to hospital admission, general symptoms, respiratory symptoms and signs), radiological and biological features, ii) to describe the hospital course and the rate of ICU transfer; in ICU patients, to describe organ failures and supports, and iii) to describe the viral and/or bacterial coinfections.