Subgroup Prevalence and Genotype Circulation Patterns of Human 1 Respiratory Syncytial Virus in Belgium during 10 Successive 2 Epidemic Seasons 3 4 Kalina

1 Human respiratory syncytial virus (HRSV) is the leading viral cause of severe respiratory 2 illness in infants and young children worldwide. Two major antigenic groups (A and B) of 3 HRSV exist and viruses from both subgroups can cocirculate during epidemics, however their 4 frequencies might vary between seasons. The subgroup prevalence and genotype distribution 5 patterns of HRSV strains were investigated in a community in Belgium during 10 successive 6 epidemic seasons (1996-2006). A regular 3-yearly cyclic pattern of subgroup dominance was 7 observed, consisting of two predominant HRSV-A seasons, followed by a single HRSV-B 8 dominant year. HRSV infections with both subgroups were more prevalent in children 9 younger that 6 months of age and had a peak incidence in December. The most frequently 10 detected genotypes were GA5 and GB13, the latter including strains with the 60-nt 11 duplication in the G gene. Furthermore, GA5 remained the dominant HRSV genotype in two 12 subsequent epidemic seasons, observed twice during the study period. Additional variability 13 was detected among the GB13 isolates, due to the usage of a novel termination codon in the G 14 gene. Dual infections with both HRSV subgroups were detected in 9 patients and repeated 15 infections with the heterologous HRSV subgroup were documented in 15 patients. Among 16 five patients with homologous reinfections, only one was caused by HRSV-B viruses. Our 17 results support the hypothesis that the overall prevalence of HRSV-A over HRSV-B viruses 18 could be due to a more transient subgroup A specific immune protection. 19