Epidemiological information: Public Health Notice - Outbreak of gastrointestinal illnesses linked to raw and undercooked oysters

March 27, 2017

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 the consumption of oysters, by week:

Dates available for 321 cases.

Symtom

Text Equivalent - Figure 1Number of people infected with E. coli non-O157

Table 1 - Reported number of clusters of norovirus or acute gastrointestinal illness associated with exposure to oysters, by week
Date of symptom onset Number of clusters
Dec 4 - 10, 2016 4
Dec 11 - 17, 2016 2
Dec 18 - 24, 2016 5
Dec 25 - 31, 2016 12
Jan 1 - 7, 2017 14
Jan 8 - 14, 2017 28
Jan 15 - 21, 2017 19
Jan 22 - 28, 2017 7
Jan 29 - Feb 4, 2017 14
Feb 5 - 11, 2017 6
Feb 12 - 18, 2017 13
Feb 19 - 25, 2017 6
Feb 26 - Mar 4, 2017 3
Mar 5 - 11, 2017 3
Mar 12- 18, 2017 3

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

Symtom2

Text Equivalent - Figure 2Number of people infected with E. coli non-O157

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
Dec 4 - 10, 2016 7
Dec 11 - 17, 2016 6
Dec 18 - 24, 2016 15
Dec 25 - 31, 2016 32
Jan 1 - 7, 2017 31
Jan 8 - 14, 2017 67
Jan 15 - 21, 2017 37
Jan 22 - 28, 2017 11
Jan 29 - Feb 4, 2017 26
Feb 5 - 11, 2017 22
Feb 12 - 18, 2017 36
Feb 19 - 25, 2017 8
Feb 26 - Mar 4, 2017 5
Mar 5 - 1, 2017 8
Mar 12 - 18, 2017 10

 

Table 2: At a Glance
Outbreak status Ongoing
Case count 321
Provinces/Territories 3
Hospitalizations Not reported
Deaths Not reported
Gender (m:f) Not reported
Age range in years Not reported
Recall No

Footnote:

Note: It can take several weeks from the time a person becomes ill to when this illness is reported and follow-up confirms a link to the outbreak.

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