Changes in norovirus incidence in Victoria, Australia, 2022: are we back to normal yet after COVID?

Abstract: There were 108 norovirus-positive outbreaks in 2022, with 45 (41.7%) occurring during the first quarter (Q1), January-March. Aged care facilities accounted for 44.4% of norovirus-positive outbreaks; 43.5% were in childcare settings. Overall, the GII.P31/GII.4 genotype was the most common, involved in 39.4% of outbreaks; however, there were shifts in the most common genotype across the year. In Q1, the GII.P31/GII.4 genotype accounted for 73.3% of typed outbreaks, but by Q3 (July-September) the GII.P7/GII.6 was the most prominent genotype at 45.0%. In Q4 (October-December), the dominant genotype had changed again to GII.P16/GII.4 (52.6%). While the incidence of norovirus outbreaks in 2022 was average regarding overall prevalence and genotype diversity, there are still ongoing effects from the coronavirus disease 2019 (COVID-19) pandemic in relation to seasonality, outbreak demographics and specimen referral.