NEW MICROBIOLOGICA, 32, 297-301, 2009 Human metapneumovirus infection in a cohort of young asymptomatic subjects Rosalinda Bruno 1 , Stefania Marsico 1 , Chiara Minini 2 , Paola Apostoli 2 , Simona Fiorentini 2 , Arnaldo Caruso 2 1 Section of Microbiology, Department of Pharmaco-Biology, University of Calabria, Rende (Cosenza), Italy; 2 Section of Microbiology, Department of Experimental and Applied Medicine, University of Brescia, Italy Corresponding author Arnaldo Caruso Section of Microbiology Department of Experimental and Applied Medicine University of Brescia Piazzale Spedali Civili, 1 - 25123 Brescia, Italy E-mail: caruso@med.unibs.it Human metapneumovirus (HMPV) was identi- fied in 2001 in the Netherlands from nasopha- ryngeal aspirate samples (Van den Hoogen et al., 2001) of children with acute respiratory infec- tions (ARI). HMPV has been classified into the subfamily pneumovirinae within the family paramyxoviridae (Van den Hoogen et al., 2001; Galiano et al., 2006) genus metapneumovirus, species human metapneumovirus. HMPV has been identified worldwide (Kahn et al., 2006) and longitudinal surveys have indicated that HMPV has a seasonal distribution, mainly occurring dur- ing winter to early spring (Van den Hoogen et al., 2001; Bastien et al., 2003; Williams et al., 2006; Caracciolo et al., 2008). Incidence of HMPV in- fection can substantially vary from year to year, being sometimes infrequent or rivaling respira- tory syncitial virus (RSV) (Maggi et al., 2003; Caracciolo et al., 2008). Based on genomic sequencing and phylogenetic analysis, there are two major genotypes of HMPV, designated A and B (Biacchesi et al., 2003; Kahn, 2006) and each genotype appears to have at least two distinct subgroups (MacKay et al., 2004). It has been shown that concurrent annual circula- tion of all four subgroups in the same geograph- ical area is common, with a single, usually dif- ferent, HMPV subgroup predominating each year (Kahn 2006; Caracciolo et al., 2008). Seroprevalence studies in the Netherlands (Van den Hoogen et al., 2001), Israel (Wolf et al., 2003) and Japan (Ebihara et al., 2003) have shown that by the age of 5 to 10 years, seropositivity reach- es virtually 100%. Moreover, reinfections have been observed in all age groups. Since its initial description, HMPV has been con- sidered a leading cause of serious lower respira- tory diseases in infants and young children (Van den Hoogen et al., 2001; Hamelin et al., 2004). Belonging to the same subfamily, HMPV is com- pared frequently with RSV because they share many biologic properties and cause a similar, but not identical, disease (Regev et al., 2006; Wolf et al., 2006; Caracciolo et al., 2008). The importance of HMPV infection in high risk adults, especially among the elderly and im- Human metapneumovirus (HMPV) is a recently described cause of respiratory infection. The purpose of this study was to to further the available information on the circulation of HMPV among young asymptomatic subjects. The epidemiology of HMPV was examined in a cohort of 73 university students during a winter season by using polymerase chain reaction. HPMV was detected in 3/73 (4.1%) asymptomatic subjects. Phylogenetic analysis has shown that circulating viruses be- longed to different HMPV sublineages. Our findings indicate that asymptomatic carriage of HMPV might be a neglected source of viral transmission in the community. KEY WORDS: Human metapneumovirus; molecular epidemiology SUMMARY Received March 03, 2009 Accepted March 15, 2009