A36 Circulating strains of human respiratory syncytial virus in Belgium during six consecutive respiratory seasons (2011–2017)

Abstract

Human respiratory syncytial virus (HRSV) is the most common cause of acute respiratory infection in young children. HRSV belongs to the Pneumoviridae family within the order of the Mononegavirales and can be divided into two subtypes: HRSV-A and HRSV-B. The two subtypes co-circulate during the annual HRSV season, which occurs between November and March in Belgium. The aim of this study was to determine the circulating HRSV subtypes and genotypes between the seasons of 2011-2012 to 2016-2017. With this information, we intend to understand the temporal phylogenetic relationships better between the circulating strains over the six seasons. Between October 2011 and February 2017, 1,272 HRSV positive patient samples from the University Hospitals of Leuven were collected. In order to determine the subtype of HRSV in each sample, we performed viral RNA extraction and qPCR. Additionally, we sequenced the hypervariable ectodomain of the glycoprotein (G) gene for both subtypes of HRSV. The G-gene is one of the targets of neutralising antibodies and is therefore under constant immunological pressure to incorporate mutations. The G-gene has been shown to be the most divergent between HRSV-A and HRSV-B subtypes. The annual HRSV epidemic in Belgium occurred every year in winter, with a median onset in November (week 44, SD 1.9) and median end in March (week 5, SD 2.4) of the following year. Out of 1,944 HRSV positive samples at the University Hospitals Leuven, 1,199 (62 per cent) were subtyped. The overall prevalence of both subtypes of HRSV is similar, with 530 (27 per cent) and 487 (25 per cent) positive samples for HRSV-A and HRSV-B respectively over the six years. Nineteen samples (1 per cent) were positive for both subtypes. Both subtypes of HRSV co-circulated, with HRSV-B dominance in the 2013-2014 season and HRSV-A dominance in the 2014-2015 season. With 81 per cent of all positive samples, children under the age of six were the most vulnerable group. Genotyping of the G-gene indicated that genotypes GA2 (HRSV-A) and GB13 (HRSV-B) were the dominant strains in seasons 2011-2012 until 2014-2015. Previous studies of the circulation of HRSV in Belgium showed co-circulation of both subtypes, which is confirmed in our data from2011 to 2017. Apart froman HRSV-B dominance in 2013-2014 and an HRSV-A dominance in 2014-2015, the prevalence of both subtypes was similar. Young children (<6) were more likely to suffer from an infection with HRSV. However, age was not related with the infecting subtype. The genotype dominance has shifted over the past twenty years: from GA5 and GB13 between 1996 and 2006 to GA2 and GB13 between 2006 and 2011. The latter were the dominant strains in other parts of the world and were still the most prevalent circulating strains in Belgiumbetween 2011 and 2015.