Table 1.
Bivariate relationships between outbreak characteristics and outcomes of attack rate, genogroup, and GII.4 strain presence for published norovirus outbreaks
| Attack Rate | Genogroup | Strain | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| GII | GI | GII and GI | GII.4 | non GII.4 | |||||||||||
| Variable | Mean | SD | p** | n | % | n | % | n | % | p** | n | % | n | % | p** |
| Transmission | 0.02* | <.01* | 0.15 | ||||||||||||
| Foodborne | 52.7 | 27.4 | 206 | 87.3 | 41 | 69.5 | 63 | 77.8 | φa | 84 | 78.5 | 161 | 82.6 | ||
| Waterborne | 44.1 | 23.5 | 22 | 9.3 | 18 | 30.5 | 18 | 22.2 | φ | 18 | 16.8 | 32 | 16.4 | ||
| Environmental | 32.2 | 24.0 | 8 | 3.4 | 0 | 0.0 | 0 | 0.0 | φb | 5 | 4.7 | 2 | 1.0 | ||
| Food Vehicles | <.01* | <.01* | 0.43 | ||||||||||||
| Produce | 48.0 | 21.2 | 17 | 18.1 | 6 | 26.1 | 1 | 1.7 | φa | 3 | 8.8 | 16 | 17.2 | ||
| Shellfish | 59.9 | 26.8 | φ | 48 | 51.1 | 9 | 39.1 | 58 | 98.3 | φ | 22 | 64.7 | 59 | 63.4 | |
| Ready to Eat | 40.9 | 25.5 | φ | 29 | 30.9 | 8 | 34.8 | 0 | 0.0 | φb | 9 | 26.5 | 18 | 19.4 | |
| Water Vehicles | <.01* | 0.73 | 0.13 | ||||||||||||
| Tap | 26.9 | 15.8 | φ | 6 | 31.6 | 6 | 42.9 | 8 | 47.1 | 8 | 50.0 | 10 | 38.5 | ||
| Ground | 45.6 | 23.4 | 10 | 52.6 | 7 | 50.0 | 7 | 41.2 | 5 | 31.3 | 15 | 57.7 | |||
| Surface | 69.8 | 11.4 | φ | 1 | 5.3 | 0 | 0.0 | 2 | 11.8 | 2 | 12.5 | 0 | 0.0 | ||
| Recreation | 34.3 | 11.0 | 2 | 10.5 | 1 | 7.1 | 0 | 0.0 | 1 | 6.3 | 1 | 3.8 | |||
| Setting | <.01* | 0.22 | 0.01* | ||||||||||||
| Foodservice | 55.1 | 25.7 | φ | 135 | 68.9 | 31 | 67.4 | 42 | 79.2 | 48 | 58.5 | 117 | 77.0 | φ | |
| Leisure | 40.6 | 22.1 | φa | 40 | 20.4 | 13 | 28.3 | 10 | 18.9 | 23 | 28.0 | 26 | 17.1 | ||
| School/Daycare | 39.9 | 21.6 | 9 | 4.6 | 2 | 4.3 | 1 | 1.9 | 3 | 3.7 | 6 | 3.9 | |||
| Healthcare | 30.4 | 16.2 | φb | 12 | 6.1 | 0 | 0.0 | 0 | 0.0 | 8 | 9.8 | 3 | 2.0 | φ | |
| Season | 0.20 | 0.01* | 0.56 | ||||||||||||
| Winter | 54.1 | 28.4 | 102 | 44.5 | 16 | 28.1 | 44 | 55.0 | 45 | 44.1 | 72 | 37.7 | |||
| Spring | 51.2 | 26.3 | 49 | 21.4 | 12 | 21.1 | 19 | 23.8 | 19 | 18.6 | 46 | 24.1 | |||
| Summer | 47.3 | 27.1 | 42 | 18.3 | 12 | 21.1 | 10 | 12.5 | 17 | 16.7 | 38 | 19.9 | |||
| Fall | 45.2 | 25.0 | 36 | 15.7 | 17 | 29.8 | 7 | 8.8 | 21 | 20.6 | 35 | 18.3 | |||
| Hemisphere | 0.17 | 1.00 | 0.04* | ||||||||||||
| Northern | 51.4 | 27.0 | 225 | 95.3 | 57 | 96.6 | 77 | 96.3 | 105 | 99.1 | 184 | 93.9 | |||
| Southern | 42.2 | 26.8 | 11 | 4.7 | 2 | 3.4 | 3 | 3.8 | 1 | 0.9 | 12 | 6.1 | |||
**
ANOVA tests for normally distributed continuous variables and Fisher exact tests for categorical variable assessment.
*
Significant at α=0.05. Significantly different means and frequencies indicated by φ. φa and φb indicate values different from φ but not each other.