RESUMEN
OBJECTIVES: To describe a human metapneumovirus (hMPV) outbreak occurring in a nursing home for older adults and to identify the risk factors associated with the clinical infection. DESIGN: A retrospective, case-controlled study. SETTING AND PARTICIPANTS: A French nursing home for older adults between December 27, 2014 and January 20, 2015. Probable cases were residents presenting at least 1 respiratory symptom or 1 constitutional symptom. Confirmed cases identified in the same way as probable cases but with a positive RT-PCR test for hMPV. Controls were residents with no symptoms of respiratory infection. MEASURES: Identification of hMPV was realized on nasal swab samples by RT-PCR. RESULTS: Seventy-eight older people were resident at the time of the outbreak. Three of the 4 tested were positive for hMPV by RT-PCR and negative for 13 other viruses or bacteria. All probable infected residents presented cough; other symptoms were scarcer. An inflammatory response was present, with median C-reactive protein at 50 mg/L. The median duration of the illness was 7 days. The rate of infection among residents was high (51%), with 5 hospitalizations (12.5%) and 1 death (2.5%). In multivariate analysis, vaccination against influenza virus appeared to emerge as associated with a probable hMPV infection, but this might be an artifact, as the proportion of unvaccinated residents was low (15%). A clear infected population profile was hard to define, although limited autonomy and low ADL score may play a role. Basic hygiene precautions were reinforced, but droplet precautions seemed difficult to apply rigorously to this population. CONCLUSIONS/IMPLICATIONS: Clinical and biological presentations were nonspecific. The rate of infection was high, highlighting the need for the rapid introduction of strict precautions to contain the infection.