An outbreak of food poisoning occurred in a large gathering of alumni attending a pre-game tailgate event at a major university football game. In just a few hours after the buffet-style luncheon was served in a tent, at least 150 of the 300 people attending developed symptoms of gastro-intestinal disease (nausea, vomiting and diarrhea). An investigation by the local health department revealed the following:

	# People who ate this food (at risk)	# People who became ill	Attack rate (Percent)	# People who did not eat food (at risk)	# People who did not eat this food but became ill	Attack Rate (Percent)
Hamburger	210	115		90	40
Chicken salad	140	135		160	20
Egg salad	70	35		130	115
Pies	240	140		60	10
Pasta salad	80	45		220	105

The attack rate is calculated as the number of people who became ill divided by the number of people at risk for the illness. Calculate the crude attack rate and then calculate the food-specific attack rate per 100 for each food for those who consumed and those who did not consumer each food. (Complete table)

1. Which food do you think is the likely cause of this common-source epidemic? Explain your choice.

2. What are the procedures that a local health department might use for investigating an outbreak of food borne illness?