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. 2023 Feb 18;76(4):667-673.
doi: 10.1093/cid/ciac627.

Spatiotemporal Trends in Norovirus Outbreaks in the United States, 2009-2019

Anita K Kambhampati  1 , Laura Calderwood  1   2 , Mary E Wikswo  1 , Leslie Barclay  1 , Claire P Mattison  1   2 , Neha Balachandran  1   2 , Jan Vinjé  1 , Aron J Hall  1 , Sara A Mirza  1
Affiliations

Spatiotemporal Trends in Norovirus Outbreaks in the United States, 2009-2019

Anita K Kambhampati et al. Clin Infect Dis. .

Abstract

Background: Globally, noroviruses cause infections year-round but have recognized winter seasonality in the Northern Hemisphere and yearly variations in incidence. With candidate norovirus vaccines in development, understanding temporal and geographic trends in norovirus disease is important to inform potential vaccination strategies and evaluate vaccine impact.

Methods: We analyzed data from the National Outbreak Reporting System (NORS) and CaliciNet on single-state norovirus outbreaks that occurred during August 2009-July 2019 in the contiguous United States. We defined norovirus season onset and offset as the weeks by which 10% and 90% of norovirus outbreaks in a surveillance year occurred, respectively, and duration as the difference in weeks between onset and offset. We compared norovirus seasons across surveillance years and geographic regions.

Results: During August 2009-July 2019, 24 995 single-state norovirus outbreaks were reported to NORS and/or CaliciNet. Nationally, the median norovirus season duration was 24 weeks, with onset occurring between October and December and offset occurring between April and May. Across all years combined, we observed a west-to-east trend in seasonality, with the earliest onset (October) and latest offset (May) occurring in western regions and the latest onset (December) and earliest offset (April) occurring in northeastern regions.

Conclusions: Timing and duration of the US norovirus season varied annually but generally occurred during October-May. Norovirus wintertime seasonality was less distinct in western regions and was progressively more pronounced moving east. Further understanding the drivers of spatiotemporal dynamics of norovirus could provide insights into factors that promote virus transmission and help guide future interventions.

Keywords: acute gastroenteritis; norovirus; seasonality; surveillance.

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Conflict of interest statement

Potential conflicts of interest. The authors: No reported conflicts of interest. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest.

Figures

Figure 1.
Figure 1.
Reported norovirus outbreaks by epidemiologic week and surveillance year, United States, August 2009–July 2019. The weekly number of outbreaks is represented by the line and presented on the left y-axis. The cumulative number of outbreaks reported each surveillance year is represented by the gray bars and presented on the right y-axis.
Figure 2.
Figure 2.
Epidemiologic curves of norovirus outbreak activity by region, United States, August 2009–July 2019. The number of outbreaks are reported by epidemiologic week (listed by month) among all years, from 2009–2019. Regions are presented in approximate geographic order, along with the total number of outbreaks reported per region and PMR. Abbreviation: PMR, peak-to-mean ratio.
Figure 3.
Figure 3.
Norovirus outbreak season onset (A), offset (B), and duration (C) by region, United States, August 2009–July 2019.
See this image and copyright information in PMC

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