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, 2012–2027
| Week | Minimum, 2012-26 | Maximum, 2012-26 | 25th perc, 2012-26 | 75th perc, 2012-26 | 2026-2027 |
|---|---|---|---|---|---|
| 1-Aug | 0 | 8 | 4 | 7 | 7 |
| 8-Aug | 1 | 17 | 3 | 8 | 6 |
| 15-Aug | 1 | 12 | 4 | 5 | 2 |
| 22-Aug | 2 | 8 | 5 | 7 | 10 |
| 29-Aug | 0 | 12 | 3 | 7 | 2 |
| 5-Sep | 0 | 14 | 5 | 10 | |
| 12-Sep | 0 | 13 | 6 | 11 | |
| 19-Sep | 1 | 15 | 4 | 12 | |
| 26-Sep | 0 | 16 | 4 | 11 | |
| 3-Oct | 2 | 15 | 5 | 11 | |
| 10-Oct | 0 | 20 | 8 | 12 | |
| 17-Oct | 0 | 18 | 7 | 12 | |
| 24-Oct | 1 | 39 | 8 | 16 | |
| 31-Oct | 0 | 32 | 13 | 24 | |
| 7-Nov | 1 | 32 | 13 | 26 | |
| 14-Nov | 0 | 39 | 13 | 21 | |
| 21-Nov | 0 | 39 | 10 | 24 | |
| 28-Nov | 2 | 93 | 26 | 49 | |
| 5-Dec | 1 | 125 | 30 | 47 | |
| 12-Dec | 0 | 92 | 26 | 47 | |
| 19-Dec | 0 | 80 | 15 | 41 | |
| 26-Dec | 1 | 107 | 20 | 51 | |
| 2-Jan | 6 | 140 | 37 | 64 | |
| 9-Jan | 3 | 168 | 34 | 54 | |
| 16-Jan | 4 | 140 | 35 | 50 | |
| 23-Jan | 7 | 174 | 43 | 56 | |
| 30-Jan | 13 | 114 | 43 | 58 | |
| 6-Feb | 10 | 99 | 47 | 64 | |
| 13-Feb | 14 | 71 | 43 | 59 | |
| 20-Feb | 6 | 76 | 50 | 59 | |
| 27-Feb | 13 | 102 | 51 | 76 | |
| 6-Mar | 22 | 66 | 36 | 55 | |
| 13-Mar | 22 | 65 | 33 | 49 | |
| 20-Mar | 5 | 66 | 31 | 48 | |
| 27-Mar | 11 | 62 | 30 | 44 | |
| 3-Apr | 8 | 63 | 30 | 42 | |
| 10-Apr | 1 | 47 | 22 | 31 | |
| 17-Apr | 2 | 37 | 23 | 34 | |
| 24-Apr | 3 | 44 | 19 | 27 | |
| 1-May | 2 | 37 | 15 | 25 | |
| 8-May | 0 | 27 | 17 | 25 | |
| 15-May | 0 | 27 | 11 | 16 | |
| 22-May | 0 | 16 | 7 | 11 | |
| 29-May | 0 | 14 | 6 | 11 | |
| 5-Jun | 0 | 16 | 7 | 8 | |
| 12-Jun | 2 | 18 | 6 | 9 | |
| 19-Jun | 1 | 15 | 5 | 10 | |
| 26-Jun | 0 | 13 | 3 | 7 | |
| 3-Jul | 1 | 10 | 4 | 6 | |
| 10-Jul | 0 | 14 | 7 | 9 | |
| 17-Jul | 0 | 13 | 4 | 9 | |
| 24-Jul | 1 | 11 | 5 | 7 |
Table notes
The NoroSTAT network includes Colorado, Michigan, Minnesota, Nebraska, New Hampshire, 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.
- Virginia joined the NoroSTAT network at the start of the 2016-17 seasonal year; 2012-16 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.
- North Carolina joined the NoroSTAT network at the start of the 2022-23 seasonal year; 2012-2022 data from this state 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.
- New Hampshire joined the NoroSTAT network at the start of the 2025-26 seasonal year; 2012-2025 data from this state were added for comparison.
Data from the NoroSTAT network are typically released online on a monthly basis.
Content Source
National Center for Immunization and Respiratory Diseases; Division of Viral Diseases
About This Page
Published: May 15, 2024
Updated: September 17, 2026
This page was last updated on this date. Updates may include minor edits, image changes, or other modifications to page content.
Reviewed: September 17, 2026
The information on this page was last reviewed by subject matter experts to ensure accuracy.