Table 1.
National Norovirus Season Characteristics by Surveillance Year, United States, 2009–2019
| Surveillance Year | Onset Week | Peak Week | Offset Week | Season Duration, Weeks | Number of Reported Norovirus Outbreaks | Peak-to-Mean Ratio |
|---|---|---|---|---|---|---|
| 2009–2010 | December 12 | February 20 | May 15 | 23 | 1201 | 3.7 |
| 2010–2011 | October 31 | December 26 | April 10 | 24 | 1651 | 3.1 |
| 2011–2012 | November 21 | January 30 | April 17 | 22 | 1814 | 3.7 |
| 2012–2013 | November 14 | February 27 | April 17 | 23 | 2408 | 2.5 |
| 2013–2014 | November 28 | March 27 | May 8 | 24 | 2593 | 2.9 |
| 2014–2015 | November 21 | February 27 | May 1 | 24 | 3012 | 3.4 |
| 2015–2016 | October 31 | March 6 | May 8 | 28 | 3026 | 2.5 |
| 2016–2017 | October 31 | January 2 | April 24 | 26 | 3122 | 3.3 |
| 2017–2018 | October 31 | January 2 | April 24 | 26 | 2953 | 3.3 |
| 2018–2019 | November 7 | January 2 | April 24 | 25 | 3215 | 2.5 |