Final answer:
The type of oil used in a fryer varies by restaurant, but guests with a shellfish allergy should avoid fried dishes if the same fryer is used for shellfish due to the risk of cross-contamination. Foodborne illnesses can be traced back to specific contaminated food items, such as improperly handled shellfish.
Step-by-step explanation:
The type of oil used in a fryer at a restaurant depends on what the establishment chooses, which could range from vegetable oil to peanut oil, among others. If a guest has a shellfish allergy, it's crucial to determine if the same fryer is used for both shellfish and other fried dishes. Cross-contamination can occur if the oil is shared between shellfish and non-shellfish items, making it unsafe for guests with a shellfish allergy to consume any fried dishes from that fryer.
Foodborne illnesses can be associated with a particular food item if that item has been contaminated. For instance, if shellfish that is improperly handled or cooked is served, it can lead to occurrences of disease among the people who ate at the restaurant. In such cases, investigators will often track the source of the illness to a specific food item that was contaminated.