Table 1. Foodborne norovirus outbreak characteristics reported to the National Outbreak Reporting System and CaliciNet, United States, August 2009–July 2015.
| Overall | GII.4* outbreaks | non-GII.4† outbreaks | P-value‡ | |
|---|---|---|---|---|
| n = 493 | n = 258 | n = 235 | ||
| Outbreak characteristics | ||||
| Number of primary cases, median (range) | 13 (2-294) | 13 (2-210) | 14 (2-294) | 0.7587 |
| Duration (in days), median (range) | 3 (1-33) | 3 (1-19) | 3 (1-33) | 0.3443 |
| Case-patient health outcomes | ||||
| Healthcare visit, n (per 100 case-patients) | 492 (5.8) | 278 (6.2) | 214 (5.4) | 0.1349 |
| Emergency department visit, n (per 100 case-patients) | 319 (2.5) | 164 (3.7) | 155 (4.0) | 0.4781 |
| Hospitalization, n (per 1,000 case-patients) | 87 (8.8) | 63 (12.8) | 24 (4.8) | < 0.0001 |
| Death, n (per 10,000 case-patients) | 4 (3.8) | 4 (7.5) | 0 (0.0) | 0.0651 |
*GII.4 Sydney (163, 33.1%), GII.4 New Orleans (86, 17.4%), GII.4 Den Haag (8, 1.6%), GII.4 Osaka (1, 0.2%)
†GII.6 (45, 9.1%), GI.3 (38, 7.7%), GI.6 (29, 5.9%), GII.1 (22, 4.5%), GII.2 (18, 3.7%), GII.12 (16, 3.3%), GII.7 (14, 2.8%), GII.3 (12, 2.4%), GI.2 (11, 2.2%), GI.4 (7, 1.4%), GI.5 (4, 0.8%), GII.13 (4, 0.8%), GII.14 (4, 0.8%), GI.7 (3, 0.6%), GII.5 (3, 0.6%), GII.17 (3, 0.6%), GI.1 (1, 0.2%), GII.25 (1, 0.2%)
‡Statistical comparisons made between GII.4 and non-GII.4 outbreaks. Mann-Whitney U-test was used to compare the median number of primary cases and median outbreak duration; Fisher's exact test was used to compare the case-patient health outcomes