Final answer:
A case-control study compares foods eaten by individuals who became ill with those who did not to find an association with a disease outbreak. Allergen tables, which provide information on potential food allergens, are usually kept within the restaurant for staff reference to prevent allergic reactions.
Step-by-step explanation:
When attempting to ascertain whether a specific food item can be linked to the outbreak of disease among patrons of a restaurant, a case-control study is often utilized, as was done with the 19 individuals who developed food poisoning and the 20 controls who did not. To determine a correlation, the consumed food items from all individuals would be compared, looking for significant discrepancies between the two groups. If a particular food item was consumed significantly more by the individuals who became ill, it could be associated with the food poisoning cases.
In the context of the allergen tables, these would typically be kept on-site at a restaurant, often in the kitchen or with the management, to ensure that staff can reference them when needed to avoid allergic reactions. The table you mentioned includes information about potential allergens such as egg and mustard, and the possible cross-contamination with gluten, milk, soya, celery sulphites, and their derivatives. It is important to note that food poisoning and allergic reactions are different issues - allergen information helps prevent allergic reactions, while food poisoning is typically related to contamination or improper food handling.