Final answer:
A foodborne illness outbreak occurs when at least two or more people eat the same food and contract the same illness. The correct answer is option b).
Step-by-step explanation:
A foodborne illness outbreak is defined as an event in which two or more people contract the same illness from consuming food from a common source. According to the Center for Disease Control and Prevention (CDC), a very small percentage of foodborne disease cases occur as part of disease outbreaks, most notably in settings like restaurants.
When investigating such outbreaks, it is essential to identify the contaminated food item through a case-control study, like in the example provided where 19 people developed food poisoning from a single restaurant. Sporadic cases are the majority of foodborne illnesses and typically do not lead to the identification of a common source.
However, an outbreak is suspected when a group experiences similar symptoms after consuming the same food, indicating a disease outbreak. Thus, the correct answer to the student's question is: b) 5.