Table 3.

Year-to-Year Seasonal Onset of Sporadic Norovirus Cases and Outbreaks

Season	Sporadic Cases (%) n = 755	Outbreaks (%) n = 45
December 2012–April 2013a	108 (14.3)	8 (17.8)
May 2013–October 2013	53 (7.0)	0
November 2013–April 2014	178 (23.6)	16 (35.6)
May 2014–October 2014	54 (7.2)	3 (6.7)
November 2014–April 2015	161 (21.3)	8 (17.8)
May 2015–October 2015	55 (7.3)	2 (4.4)
November 2015–April 2016	119 (15.8)	7 (15.6)
May 2016–June 2016	27 (3.6)	1 (2.2)

^aAlthough the 2012 winter season began in November, New Vaccine Surveillance Network data collection did not begin until December 2012.