Key points
- The table shows data on suspected and confirmed norovirus outbreaks reported to CDC by NoroSTAT-participating state health departments.
- States report data through the National Outbreak Reporting System (NORS).
- Outbreaks in the data table are classified by week of illness onset and updated monthly.
Data table
Norovirus Outbreaks Reported by State Health Departments by Week of Illness Onset, 2012–2025
| Week | Minimum, 2012-20 | Maximum, 2012-20 | 2020-21 | Minimum, 2021-24 | Maximum, 2021-24 | 2024-25 |
|---|---|---|---|---|---|---|
| 1-Aug | 1 | 9 | 0 | 5 | 8 | 8 |
| 8-Aug | 2 | 17 | 1 | 2 | 7 | 7 |
| 15-Aug | 4 | 13 | 1 | 6 | 7 | 6 |
| 22-Aug | 5 | 10 | 2 | 3 | 7 | 9 |
| 29-Aug | 0 | 13 | 1 | 4 | 6 | 11 |
| 5-Sep | 4 | 13 | 0 | 3 | 14 | 14 |
| 12-Sep | 5 | 16 | 1 | 7 | 15 | 13 |
| 19-Sep | 4 | 15 | 1 | 11 | 14 | 21 |
| 26-Sep | 4 | 17 | 0 | 4 | 12 | 11 |
| 3-Oct | 3 | 16 | 2 | 7 | 16 | 13 |
| 10-Oct | 5 | 21 | 0 | 9 | 20 | 20 |
| 17-Oct | 4 | 18 | 0 | 3 | 16 | 19 |
| 24-Oct | 5 | 18 | 1 | 9 | 18 | 39 |
| 31-Oct | 13 | 27 | 0 | 9 | 30 | 20 |
| 7-Nov | 9 | 28 | 2 | 8 | 33 | |
| 14-Nov | 14 | 27 | 0 | 8 | 20 | |
| 21-Nov | 11 | 41 | 0 | 6 | 24 | |
| 28-Nov | 27 | 65 | 2 | 12 | 56 | |
| 5-Dec | 35 | 65 | 2 | 17 | 41 | |
| 12-Dec | 26 | 86 | 0 | 14 | 43 | |
| 19-Dec | 15 | 55 | 0 | 12 | 19 | |
| 26-Dec | 23 | 69 | 1 | 16 | 28 | |
| 2-Jan | 35 | 92 | 6 | 15 | 47 | |
| 9-Jan | 29 | 66 | 3 | 12 | 57 | |
| 16-Jan | 33 | 93 | 4 | 17 | 60 | |
| 23-Jan | 42 | 83 | 7 | 39 | 53 | |
| 30-Jan | 45 | 66 | 15 | 45 | 59 | |
| 6-Feb | 41 | 72 | 10 | 49 | 71 | |
| 13-Feb | 35 | 61 | 18 | 56 | 69 | |
| 20-Feb | 24 | 68 | 10 | 56 | 65 | |
| 27-Feb | 35 | 78 | 15 | 76 | 107 | |
| 6-Mar | 33 | 67 | 26 | 56 | 66 | |
| 13-Mar | 32 | 50 | 25 | 52 | 76 | |
| 20-Mar | 11 | 55 | 28 | 40 | 68 | |
| 27-Mar | 10 | 60 | 29 | 40 | 62 | |
| 3-Apr | 5 | 57 | 42 | 52 | 70 | |
| 10-Apr | 1 | 34 | 52 | 31 | 40 | |
| 17-Apr | 1 | 31 | 38 | 37 | 38 | |
| 24-Apr | 3 | 28 | 23 | 35 | 45 | |
| 1-May | 2 | 27 | 24 | 25 | 43 | |
| 8-May | 1 | 28 | 27 | 17 | 25 | |
| 15-May | 0 | 31 | 18 | 16 | 21 | |
| 22-May | 0 | 18 | 6 | 8 | 12 | |
| 29-May | 0 | 13 | 13 | 5 | 11 | |
| 5-Jun | 0 | 12 | 10 | 1 | 13 | |
| 12-Jun | 2 | 13 | 9 | 4 | 11 | |
| 19-Jun | 1 | 12 | 12 | 7 | 13 | |
| 26-Jun | 1 | 8 | 6 | 5 | 7 | |
| 3-Jul | 2 | 10 | 7 | 1 | 4 | |
| 10-Jul | 1 | 12 | 11 | 7 | 14 | |
| 17-Jul | 0 | 11 | 5 | 2 | 12 | |
| 24-Jul | 2 | 11 | 5 | 4 | 7 |
Table notes
The NoroSTAT network includes Alabama, Colorado, Massachusetts, Michigan, Minnesota, Nebraska, New Mexico, North Carolina, Ohio, Oregon, South Carolina, Tennessee, Virginia, and Wisconsin.
- Michigan and South Carolina joined the NoroSTAT network at the start of the 2015-16 seasonal year; 2012-15 data from these states were added for comparison.
- Massachusetts and Virginia joined the NoroSTAT network at the start of the 2016-17 seasonal year; 2012-16 data from these states were added for comparison.
- New Mexico joined the NoroSTAT network at the start of the 2018-19 seasonal year; 2012-2018 data from this state were added for comparison.
- Nebraska joined the NoroSTAT network at the start of the 2019-20 seasonal year; 2012-2019 data from this state were added for comparison.
- Alabama and North Carolina joined the NoroSTAT network at the start of the 2022-23 seasonal year; 2012-2022 data from these states were added for comparison.
- Colorado joined the NoroSTAT network at the start of the 2023-24 seasonal year; 2012-2023 data from this state were added for comparison.
Data from the NoroSTAT network are typically released online on a monthly basis.