Rapid spread of the novel respiratory syncytial virus A ON1 genotype, central Italy, 2011 to 2013

Abstract

Respiratory infections positive for human respiratory syncytial virus (RSV) subtype A were characterised in children admitted to hospitals in Rome and Ancona (Italy) over the last three epidemic seasons. Different strains of the novel RSV-A genotype ON1, first identified in Ontario (Canada) in December 2010, were detected for the first time in Italy in the following 2011/12 epidemic season. They bear an insertion of 24 amino acids in the G glycoprotein as well as amino acid changes likely to change antigenicity. By early 2013, ON1 strains had spread so efficiently that they had nearly replaced other RSV-A strains. Notably, the RSV peak in the 2012/13 epidemic season occurred earlier and, compared with the previous two seasons, influenza-like illnesses diagnoses were more frequent in younger children; bronchiolitis cases had a less severe clinical course. Nonetheless, the ON1-associated intensive care unit admission rate was similar, if not greater, than that attributable to other RSV-A strains. Improving RSV surveillance would allow timely understanding of the epidemiological and clinicopathological features of the novel RSV-A genotype.

Viral/bacterial respiratory tract co-infections in children

“…In 2010, an NA1 variant with a 72 nucleotide duplication in HVR2 was identified in Ontario, Canada (genotype ON1) (203,207). ON1 and similar NA1 variants with the large duplication have since been reported worldwide, although they have yet to replace GA2, NA1 and GA5 in the population (192,194,195,197,198,202,203,215,216).…”

“…However, it has been suggested that successful new genotypes may possess novel antigenicity and thus ability to evade host immunity, resulting in hospitalisation spikes on introduction to a naive population, such as associated with the emergence of ON1, without an inherent ability to cause more severe disease (197,201). This hypothesis is consistent with the increases in hospital and ICU admissions associated with ON1 compared to other RSV strains (197,198), and the large epidemics associated with NA1 and NA2 when they first emerged in Japan in the mid 2000s but not observed since (201 (227). Antibiotic resistance is a growing problem with many bacterial pathogens, and resistance has been observed in S. pneumoniae to both first-and second-line antibiotics commonly used to treat bacterial pneumonia (75)(76)(77)81).…”

“…ON1 has been reported to be associated with increased ARI severity (223), reduced severity (195,197) and no difference between ON1 and other circulating RSV strains (202).…”

“…The ectodomain of G contains two hypervariable regions separated by a putative receptor binding domain that is conserved in both RSV-A and RSV-B. The second C-terminal hypervariable region (HVR2) is sufficient for distinguishing between subtypes and has thus been used by the majority of studies investigating RSV genetic diversity (190,(193)(194)(195)(196)(197)(198)(199)(200)(201)(202)(203)(204). More recently, whole genome sequencing has also been applied to RSV strains from various clinical settings (188,189,191,192), adding valuable information to our understanding of RSV evolution.…”

“…S. pneumoniae colonisation of the URT has been shown to vary between different serotypes and strains (76,242). Previous epidemiological studies of ARI have described the genetic diversity of RSV based on G (190,(193)(194)(195)(196)(197)(198)(199)(200)(201)(202)(203)(204). Studies of serotype distribution and genetic diversity of S. pneumoniae during asymptomatic carriage and disease have also been performed (75, 76, 79-81, 227, 245, 247, 250, 287), and some studies of paediatric LRT infections have reported pneumococcal serotypes in addition to respiratory virus and bacteria detections (99,104,228,(288)(289)(290).…”