In 2001, van den Hoogen et al. reported the isolation of a novel paramyxovirus, human metapneumovirus (HMPV) from children with respiratory tract disease (2) . HMPV has been identified worldwide (3) (4) (5) (6) (7) and appears to have a seasonal distribution (winter and spring) (8) . Since the circulation of HMPV may overlap with that of RSV, simultaneous infection with both RSV and HMPV may contribute to severe disease. Greensill et al. (9) reported that 70% of RSV-infected children who required admission to the Pediatric Intensive Care Unit (PICU) in Liverpool, U.K. were co-infected with HMPV.