Epidemiological information: Outbreak of norovirus infections linked to raw oysters

August 1, 2018

What is epidemiology?

Epidemiology is the study of disease in a population. Epidemiologists, or "disease detectives," use surveillance systems to identify those who are sick and confirm that the sick people are part of this event. They then gather information from the people who got sick and review the clues from all parts of the investigation that might reveal the cause of the illness event.

The figure below forms part of the epidemiological investigation into this outbreak. An "epi curve" (Figure 1) is a valuable reference tool in any epidemiological investigation. An epi curve shows when cases begin, when they peak, and when they trail off. Certain details of the people who got sick (Table 1) also help epidemiologists as they work to solve the questions involved in foodborne illness.

Figure 1: Reported number of clusters of norovirus or acute gastrointestinal illness associated with exposures to oysters, by week

Figure 1

Figure 1: Reported number of clusters of norovirus or acute gastrointestinal illness associated with exposures to oysters, by week - Text equivalent

Table 1 – Reported number of clusters of norovirus or acute gastrointestinal illness associated with exposures to oysters, by week
Week of symptom onset Number of clusters
11-Mar-2018 2
18-Mar-2018 10
25-Mar-2018 21
1-Apr-2018 22
8-Apr-2018 12
15-Apr-2018 4
22-Apr-2018 0
29-Apr-2018 0
6-May-2018 0

Figure 2: Reported number of cases of norovirus or acute gastrointestinal illness associated with consumption of oysters, by week

Figure 2

Figure 2: Reported number of cases of norovirus or acute gastrointestinal illness associated with consumption of oysters, by week
Table 2: Reported number of cases of norovirus or acute gastrointestinal illness associated with exposure to oysters, by week
Week of symptom onset Number of cases
11-Mar-2018 9
18-Mar-2018 24
25-Mar-2018 67
1-Apr-2018 49
8-Apr-2018 18
15-Apr-2018 9
22-Apr-2018 0
29-Apr-2018 0
6-May-2018 0
Table 3
Outbreak status Ongoing
Case count 176
Provinces/Territories 3
Deaths 0
Recall No
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