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

February 14, 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 221 cases.

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

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

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

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.