What to know
- Below are confirmed norovirus outbreaks submitted to CaliciNet and updated monthly.
- Participating public health laboratories electronically submit genotype information for norovirus and basic epidemiology data from norovirus outbreaks to the CaliciNet database.
- The data on norovirus strains are compared with existing norovirus sequences in the CaliciNet database.
Genotype distribution of norovirus outbreaks
September 1, 2025 – May 31, 2026 (n=131)
![Bar chart showing GII.4 Sydney[P16] accounts for 51% of norovirus outbreaks, with all other categories below 23%.](/norovirus/images/genotype-distribution-norovirus-outbreaks_5-31-2026.png)
Data Table: September 1, 2025 – May 31, 2026 (n=131)
| Genotype | Number of Outbreaks |
|---|---|
| GII.4 Sydney[P16] | 67 |
| GII.17[P17] | 22 |
| GII.7[P7] | 11 |
| Other Genotypes | 31 |
The Other Genotypes category includes genotypes from outbreaks that each make up less than 5% of the total number of outbreaks. These genotypes are: GI.1[P1] (1.5%), GI.2[P2] (1.5%), GI.3[P3] (3.8%), GI.3[P13] (2.3%), GI.5[P5] (0.8%), GI.6[P11] (1.5%), GI.7[P7] (1.5%), GII.1[P33] (2.3%), GII.3[P12] (2.3%), GII.6[P7] (2.3%), GII.9[P7] (2.3%).
Data Table: September 1, 2024 – August 31, 2025 (n=411)
| Genotype | Number of Outbreaks |
|---|---|
| GII.17[P17] | 306 |
| GII.4 Sydney[P16] | 43 |
| GII.6[P7] | 16 |
| Other Genotype | 46 |
Dual typing for norovirus
Dual typing for norovirus is being implemented by laboratories participating in CaliciNet.
Dual typing is RT-PCR amplification of a partial region of both the polymerase gene and the capsid gene (region B-C) in a single reaction for genogroup I or genogroup II noroviruses.