Volume 9, Number 1—January 2003
Research
Two Epidemiologic Patterns of Norovirus Outbreaks: Surveillance in England and Wales, 1992–2000
Table 3
Setting | Median (days) | N | Geometric mean of duration (days)(95% CI)a | t test | p value |
---|---|---|---|---|---|
Duration of outbreaks |
|||||
Hospital |
8 |
679 |
8.8 (8.4 to 9.3) |
||
Residential facilities |
9 |
664 |
8.7 (8.1 to 9.4) |
–0.321 |
0.73 |
School |
8 |
63 |
8.1 (6.8 to 9.7) |
–0.879 |
0.40 |
Food outlet |
3 |
94 |
3.3 (2.8 to 3.8) |
–12.699 |
<0.0001 |
Hotel |
5 |
133 |
4.3 (3.6 to 5.1) |
–7.025 |
<0.0001 |
Other |
4 |
69 |
4.3 (3.6 to 5.1) |
–8.043 |
<0.0001 |
All settings |
8 |
1,702 |
7.7 (7.5 to 8.0) |
||
Numbers affected per outbreak |
|||||
Hospital |
17 |
751 |
17.5 (16.4 to 18.5) |
||
Residential facilities |
23 |
723 |
21.5 (19.8 to 23.3) |
4.895 |
<0.0001 |
School |
24 |
73 |
24.9 (20.5 to 30.3) |
3.594 |
<0.0001 |
Food outlet |
23 |
104 |
23.4 (19.8 to 27.6) |
3.444 |
0.001 |
Hotel |
29 |
147 |
26.5 (23.0 to 30.6) |
5.729 |
<0.0001 |
Other |
29 |
74 |
24.5 (20.2 to 29.7) |
3.432 |
0.001 |
All settings | 21 | 1,872 | 20.3 (19.7 to 21.1) |
aCI, confidence interval.
Appendix: Surveillance and analysis definitions
Outbreak: an incident in which two or more people, thought to have a common exposure, experience a similar illness or proven infection, at least one of them being ill (22).
General outbreak: an outbreak that affects members of more than one household, or residents of an institution (36).
General outbreak of Norovirus: a general outbreak in which Norovirus is determined to be the causative agent by electron microscopy, RT-PCR, or enzyme immunoassay in one or more affected persons.
Residential facilities: includes residential homes, which provide some assistance in day-to-day living, and nursing homes, which provide care for persons whose infirmity or illness requires nursing care on a regular basis.
Food outlets: commercial food retailers including restaurants, pubs, bars, cafeterias, mobile food vendors, and caterers.