Table 1.
Comparative analysis of the number of primary cases, persons at risk and primary attack rate by mode of transmission and setting.
| Variable | Outbreaks n (%) |
Analysed Sample* |
Primary Cases Median (IQR) |
Persons at Risk Median (IQR) |
Primary Attack Rate Median (IQR) |
|---|---|---|---|---|---|
| Transmission†‡ | |||||
| Foodborne | 362 (54) | 252 | 20 (9–55) | 50 (18–150) | 50% (31–71%) |
| Person-to-Person | 174 (26) | 118 | 69 (36–175)§ | 262 (108–1888)§ | 27% (12–46%)§‖ |
| Waterborne | 70 (11) | 43 | 61 (40–175)§ | 160 (81–672)§ | 38% (28–64%) |
| Environmental | 60 (9) | 47 | 108 (35–252)§ | 492 (135–2442)§ | 26% (9–41%)§‖ |
| Total | 666 | 460 | 40 (15–104) | 111 (32–414) | 40% (21–62%) |
| Setting¶ | |||||
| Foodservice | 294 (35) | 209 | 15 (7–38) | 33 (14–94) | 53% (33–75%) |
| Healthcare | 225 (27) | 123 | 22 (6–53) | 101 (70–200)** | 20% (6–34%)** |
| Leisure | 140 (17) | 114 | 58 (22–158)**†† | 211 (80–1280)** | 29% (11–48%)**†† |
| School/Daycare | 80 (10) | 44 | 40 (13–84)** | 144 (45–266)** | 28% (13–46%)** |
| Other | 91 (11) | 51 | 58 (13–300)**†† | 250 (23–2500)** | 36% (13–67%)**†† |
| Total | 830 | 541 | 26 (10–70) | 84 (33–240) | 36% (16–58%) |
Complete information was not available for all outbreaks. Summary statistics were calculated for a subset of the outbreaks, described in the “Outbreaks” column, with information on all three of the following variables: the number of primary cases, persons at risk, and primary attack rate.
Foodborne outbreaks included those associated with NoV infection following consumption of shellfish or other foods contaminated during production or preparation by an infected foodhandler. Person-to-person outbreaks included those associated with NoV infection following direct contact with vomitus or other aerosolized viral particles. Waterborne outbreaks included those associated with ingestion of infected drinking or recreational water. Environmental outbreaks included those associated with NoV infection following direct physical contact with contaminated surfaces.
Up to three modes of transmission may have been listed per outbreak. Outbreaks may therefore be listed under more than one mode of transmission.
Significantly different from foodborne transmission at p < 0.05.
Significantly different from waterborne transmission at p < 0.05.
Foodservice settings included restaurants, wedding receptions and other catered functions. Healthcare settings included hospitals, emergency rooms, clinics, psychiatric institutions, nursing homes, and assisted living facilities. Leisure settings included hotels, cruise ships, tour buses, camps, and ski lodges. School/daycare settings included primary, secondary, elementary, middle and high schools, as well as daycares, colleges, and universities. Other outbreak settings included residential, military and jail settings.
Significantly different from foodservice settings at p < 0.05.
Significantly different from healthcare settings at p < 0.05.