Rapid spread of the novel respiratory syncytial virus A ON1 genotype, during the epidemic seasons 2011-2013

Background Respiratory Syncytial Virus (RSV) is a major cause of lower respiratory-tract infection in infants. Based on reactions with monoclonal antibodies against glycoproteins G, RSV has been classified into subtypes A and B. Aim In this study, RSV-A positive cases were genotyped to evaluate the genetic variability which can modify RSV epidemic and clinical severity. Methods During 3 epidemic seasons children presenting with respiratory symptoms at the Pediatric Emergency, “Sapienza” University of Rome (RM), and at the Pediatric Department of Marche Polytechnic University (AN)were enrolled and tested for RSV with PCR on nasal washings. RSV positive samples were randomly selected for genomic characterization. Demographic and clinical data were taken from patients9 medical files. Results 515 RSV-positive infants were detected: 165 in RM (median age 2.75m; range 0.2-29m) and 350 in AN (median age 3.0m; range 0.1-163m). 161/360 RSV-A positive samples were sequenced. 15 in RM and 51 in AN strains grouped with the novel genotype ON1 which is characterized by a 72-nt insertion in G resulting in 24 extra aa. ON1 was not detected in RM neither in AN samples during 2010-11 season; it accounted for 14/61 strains (22.9%) analyzed in 2011-12 and for 52/59 strains (88.1%) in 2012-13. Clinical data showed that ON1 infection was more frequent in younger infants and caused less frequently a severe disease. Conclusion We document the presence of ON1 genotype in Italy in the 2011-12 epidemic season and its rapid spread in 2012-13. The novel genotype does not seem to possess special severity determinants compared with previously circulating RSV-A strains.