An outbreak of severe respiratory tract infection due to human metapneumovirus in a long-term care facility

Background. Human metapneumovirus (hMPV) is a newly described paramyxovirus that is mainly associated with bronchiolitis in children. We sought to describe the epidemiological, virological, and histopathological findings associated with a large outbreak of hMPV infection in a long-term care facility. Methods. An investigation of the outbreak was performed by public health authorities, who used standardized questionnaires to collect relevant clinical information from all residents of the facility. Nasopharyngeal samples were obtained from a subset of patients who had influenza-like illnesses for testing by viral culture and reverse-transcriptase polymerase chain reaction. Lung tissue samples from a patient whose case was fatal were available for molecular, histopathological, and immunohistochemical testing. Results. A total of 96 (27%) of 364 residents of a long-term care facility presented with respiratory or constitutional symptoms between 1 January 2006 and 15 February 2006. The attack rate in the most affected ward was 72% ( 31 of 43 patients), which included 4 of the 6 polymerase chain reaction - confirmed cases of hMPV infection. In contrast, viral culture results were positive for hMPV in only 2 of the 5 polymerase chain reaction positive samples tested. The most reported diagnosis was an upper respiratory tract infection or an influenza-like illness, although 21% of residents in 1 of the 3 wards that had confirmed cases of hMPV infection had lower respiratory tract infections. The fatality rate was 50% ( 3 of 6 patients) among confirmed cases and 9.4% ( 9 of 96 patients) among patients with possible cases. A patient with a fatal case had histopathological findings that confirmed the presence of hMPV RNA and proteins in the bronchiolar epithelium of affected lobes. Phylogenetic analysis revealed the presence of 2 distinct strains of hMPV circulating simultaneously on different wards. Conclusion. hMPV can be associated with important outbreaks of acute respiratory tract infection in elderly institutionalized persons.