Tracking norovirus diversity at a global scale through wastewater metagenomics

Norovirus is a leading cause of gastroenteritis globally. Understanding the emergence, evolution, and trends in norovirus genotype/strain diversity is essential to develop sustainable strategies to guide the development of interventions. Here, we used urban wastewater samples to assess and compare the diversity of noroviruses worldwide. By using a metagenomics approach, we analyzed 327 sewage samples, collected from 62 cities across 6 continents, collected over the course of two years between 2017 and 2019. Norovirus sequences were found in >80 % of the samples, yielding 7609 contigs. We identified a total of 34 capsid genotypes and 44 polymerase P-types, predominantly belonging to genogroups known to infect humans, including: GI, GII, GIV, GVIII and GIX. Changes in diversity over time were detected, along with seasonal variations in wastewater. Some rarely reported genotypes/P-types were found to be widespread, showing the potential of wastewater surveillance to complement traditional surveillance. Phylogenetic analyses revealed that in several instances, wastewater sequences were closely related to sequences reported in outbreaks of the same region. However, novel clusters were also found in locations where fewer or no sequences from outbreaks are available (e.g., African regions). The use of metagenomic sequencing for wastewater-based epidemiology has the potential to uncover the diversity of norovirus circulating in the population, being especially helpful for those regions where classical surveillance programs are not well established.