Endemicity of human metapneumovirus subgenogroups A2 and B2 in Yamagata, Japan, between 2004 and 2009

To clarify a longitudinal epidemiology,we isolated 280 hMPV strains from patients with acute respiratory infections in Yamagata, Japan, between 2004 and 2009.We observed that the high season for hMPV was from winter to spring (between January and May) and the low season was in the fall (around September and October). A further molecular analysis revealed that subgenogroup A2 (A2) strains were the most commonly isolated (151/280; 53.9%), followed by B2 (108/280; 38.6%) and B1 (19/280; 6.8%). Our results suggested that A2 and B2 have been endemically in circulation as the major types almost every year, whereas other subgenogroups have appeared less frequently.