What causes watery diarrhea that occurs 2 hours after consuming potato salad?

The correct answer is Staphylococcus aureus, which is known for causing rapid-onset food poisoning. When individuals consume foods contaminated with this bacterium, such as potato salad that may have been improperly stored, they can experience symptoms of watery diarrhea within a few hours after consumption. This is due to the preformed enterotoxins that Staphylococcus aureus produces, which can act quickly on the gastrointestinal tract.

In the case of general foodborne illnesses, Staphylococcus aureus is particularly notable for its ability to cause symptoms within a short time frame—often within 1 to 6 hours after ingestion of contaminated food. This aligns well with the timing indicated in the scenario.

Other organisms listed, like Bacillus cereus, typically results in a different onset timing based on whether it is the emetic or diarrheal type, with symptoms appearing a bit later. Norovirus usually causes diarrhea but is also associated with longer incubation periods and additional symptoms such as vomiting. Giardia lamblia is a protozoan parasite that leads to chronic diarrhea with a longer incubation period, usually from days to weeks after ingestion. Thus, these characteristics help confirm Staphylococcus aureus as the most fitting cause for the rapid onset of watery diarrhea in this particular context