Question

Community members who attended the Annual Neighborhood picnic earlier today are experiencing illness which they believe are related to food served at the picnic. Using the table below:

Calculate the attack rate for the 1) baked ham, 2) spinach, and 3) cabbage salad. Show your work.

Which food (of the baked ham, spinach, and cabbage salad) is MOST LIKELY to have caused the illness? Discuss your answer.

	Annual Neighborhood Picnic
	Number of Persons Who				Number of Persons Who
	Ate Specified Food				Did Not Eat Specified Food
Food	Ill	Well	Total		Ill	Well	Total
Baked Ham	29	17	46		17	12	29
Spinach	26	17	43		20	12	32
Mashed potatoes	23	14	37		23	14	37
Cabbage salad	18	10	28		28	19	47
Jello	16	7	23		30	22	52
Rolls	21	16	37		25	13	38
Brown bread	18	9	27		28	20	48

Answer 1

Attack Rate

For Exposed Group, the attack rate equals the number of people who ate item and became ill divided by the total number of people who ate that item.

For the not Exposed Group, the attack rate equals the number of people who did not eat but still became ill divided by the total number of people did not eat that item.

Food	Attack Rate (For Exposed)	Attack Rate (Not Exposed)
Baked ham	(29/46)*100 = 63.04%	(17/29)*100 = 58.62%
Spinach	(26/43)*100 = 60.47%	(20/32)*100 = 62.5%
Cabbage salad	(18/28)*100 = 64.29%	(28/47)*100 = 59.57%

For finding out the item that is MOST LIKELY to have caused the illness, we need to calculate relative risk.

Relative risk is calculated by dividing the attack rate of people who were exposed to the item by attack rate of those who were not exposed to the item.

Food	Relative Risk
Baked ham	63.04/58.62 = 1.075
Spinach	60.47/62.50 = 0.968
Cabbage salad	64.29/59.57 = 1.079

In this case, cabbage salad is MOST LIKELY to have caused the illness as it has the highest relative risk.