Which of the following is a key sign of foodborne illness?

The key sign of foodborne illness is the sudden onset of fever and vomiting. These symptoms are commonly associated with a host of pathogens that can contaminate food, including bacteria, viruses, and parasites. When the body detects these harmful microorganisms, it often responds with symptoms like nausea, vomiting, and fever as ways to expel the harmful agents. The acute nature of these symptoms usually indicates an infection, making it crucial for individuals experiencing them to seek medical attention, especially if they coincide with recent food consumption.

Feeling sleepy after eating, increased appetite, and feeling extremely energetic are not typical signs of foodborne illness. In fact, those symptoms could be related to various other, less serious factors such as food choices, metabolic responses, or general health, rather than indicating an illness caused by contaminated food.