Wide Diversity of Recombinant Noroviruses Circulating in Spain, 2016 to 2020

Noroviruses are the leading cause of sporadic cases and outbreaks of viral gastroenteritis. For more than 20 years most norovirus infections have been caused by the pandemic genotype GII.4, yet recent studies have reported the emergence of recombinant strains in many countries. In the present study, 4,950 stool samples collected between January 2016 and April 2020 in Valencia (Spain) from patients with acute gastroenteritis were analyzed to investigate the etiological agent. Norovirus was the most frequently detected enteric virus with a positive rate of 9.5% (471/4,950). Among 224 norovirus strains characterized, 175 belonged to genogroup GII and 49 to genogroup GI. Using dual genotyping based on sequencing the ORF1/ORF2 junction region we detected 25 different capsid-polymerase type associations. The most common GII capsid genotype was GII.4 Sydney 2012, followed by GII.2, GII.3, GII.6 and GII.17. A high prevalence of recombinant strains (90.4%) was observed among GII infections between 2018 and 2020. GII.4 Sydney[P16] was the predominant genotype from 2019 to 2020. In addition, GII.P16 polymerase was found harboring within six different capsid genes. A new subcluster of GII.4 Sydney associated with the P31 polymerase was identified by phylogenetic analysis. GI.4 and GI.3 were the predominant genotypes in genogroup GI, in which recombinant strains were also found, such as GI.3[P10], GI.3[P13] and GI.5[P4]. Interestingly, the GI.3[P10] strain could represent a new capsid genotype. This study shows the extensive diversity of recombinant noroviruses circulating in Spain and highlights the role of recombination events in the spread of noroviruses.