1
, 4. What is the diarrhea attack rate in persons who ate both ice cream & pizza?
a. 39/52
b. 21/70
c. 39/67
d. 51/67
e. None of the above
Rationale:
The attack rate in this example is defined as the number of persons who develop diarrhea
divided by the total number of people at risk. In this example, the at-risk group is those who
have eaten both ice cream & pizza. Of these 52 persons, 39 developed diarrhea.
5. What is the overall attack rate in persons who did not eat ice cream?
a. 30%
b. 33%
c. 35%
d. 44%
e. 58%
Rationale:
The attack rate is the number of persons with diarrhea (14 + 9) divided by the total number of
persons who did not eat ice cream (40 + 30).
6. Which of the food items (or combination of items) is most likely to be the infective item(s)?
a. Pizza only
b. Ice cream only
c. Neither pizza or ice cream
d. Both pizza & icecream
e. Cannot be assumed from the data shown
Among persons eating ice cream, over 70% developed diarrhea regardless of their pizza
consumption (39/52 & 11/15). Among both groups of persons who did not eat ice cream, each
attack rate was equal to or less than 35% (14/40 & 9/30).
7. Which of the following reasons can explain why a person who did not consume
the infective food item got sick?
a. They were directly exposed to persons who did eat the infective food item
b. Diarrhea is a general symptom consistent with a number of illnesses
c. There may have been an inaccurate recall of which foods were eaten
, d. All of the above
e. None of the above
Rationale: Without knowledge as to the specific agent in this instance, it is also likely that it
can be spread by direct contact with infected persons. Since diarrhea is a general disease
symptom, it is possible that several infectious agents may be present at this meal or others
eaten during the same time period. Further, information regarding food consumption may have
been collected long after the disease episode. This may have led persons to incorrectly
remember the foods that they consumed.
An outbreak of gastroenteritis occurred at a boarding school with a student enrollment of 846. Fifty-
seven students reported symptoms including vomiting, diarrhea, nausea, & low-grade fever between 10
p.m. on September 24 & 8 p.m. on September 25. The ill students lived in dormitories that housed 723 of
the students. The table below provides information on the number of students per type of residence &
the number reporting illnesses consistent with the described symptoms & onset time. Calculate the
attack rate among all students at the boarding school.
1. Calculate the attack rate among all students at the boarding school.
57/846 = The answer is found by dividing the total number of cases (57) by the
total number of students (846). This equals 6.7%.
10. Calculate the attack rates for boys & girls separately.
a. For boys, the attack rate includes all cases (40 + 3) divided by the total number of students who are
boys (380 + 46). The attack rate is 10.1%.
b. For girls, the attack rate includes all cases (12 + 2) divided by the total number of students who are
girls (343 + 77). The attack rate is 3.3%.
11. What is the proportion of total cases occurring in boys?
Answer: The proportion of cases occurring in boys is equal to the number of cases in boys divided by the
total number of cases (43/57). This equals 75.4%.
12. What is the proportion of total cases occurring in students who live in dormitories?
Answer: The proportion of cases occurring in dormitory residents is equal to the number of cases in
residents divided by the total number of cases (52/57). This equals 91.2%.
13. Which proportion is more informative for the purpose of the outbreak investigation?
, 4. What is the diarrhea attack rate in persons who ate both ice cream & pizza?
a. 39/52
b. 21/70
c. 39/67
d. 51/67
e. None of the above
Rationale:
The attack rate in this example is defined as the number of persons who develop diarrhea
divided by the total number of people at risk. In this example, the at-risk group is those who
have eaten both ice cream & pizza. Of these 52 persons, 39 developed diarrhea.
5. What is the overall attack rate in persons who did not eat ice cream?
a. 30%
b. 33%
c. 35%
d. 44%
e. 58%
Rationale:
The attack rate is the number of persons with diarrhea (14 + 9) divided by the total number of
persons who did not eat ice cream (40 + 30).
6. Which of the food items (or combination of items) is most likely to be the infective item(s)?
a. Pizza only
b. Ice cream only
c. Neither pizza or ice cream
d. Both pizza & icecream
e. Cannot be assumed from the data shown
Among persons eating ice cream, over 70% developed diarrhea regardless of their pizza
consumption (39/52 & 11/15). Among both groups of persons who did not eat ice cream, each
attack rate was equal to or less than 35% (14/40 & 9/30).
7. Which of the following reasons can explain why a person who did not consume
the infective food item got sick?
a. They were directly exposed to persons who did eat the infective food item
b. Diarrhea is a general symptom consistent with a number of illnesses
c. There may have been an inaccurate recall of which foods were eaten
, d. All of the above
e. None of the above
Rationale: Without knowledge as to the specific agent in this instance, it is also likely that it
can be spread by direct contact with infected persons. Since diarrhea is a general disease
symptom, it is possible that several infectious agents may be present at this meal or others
eaten during the same time period. Further, information regarding food consumption may have
been collected long after the disease episode. This may have led persons to incorrectly
remember the foods that they consumed.
An outbreak of gastroenteritis occurred at a boarding school with a student enrollment of 846. Fifty-
seven students reported symptoms including vomiting, diarrhea, nausea, & low-grade fever between 10
p.m. on September 24 & 8 p.m. on September 25. The ill students lived in dormitories that housed 723 of
the students. The table below provides information on the number of students per type of residence &
the number reporting illnesses consistent with the described symptoms & onset time. Calculate the
attack rate among all students at the boarding school.
1. Calculate the attack rate among all students at the boarding school.
57/846 = The answer is found by dividing the total number of cases (57) by the
total number of students (846). This equals 6.7%.
10. Calculate the attack rates for boys & girls separately.
a. For boys, the attack rate includes all cases (40 + 3) divided by the total number of students who are
boys (380 + 46). The attack rate is 10.1%.
b. For girls, the attack rate includes all cases (12 + 2) divided by the total number of students who are
girls (343 + 77). The attack rate is 3.3%.
11. What is the proportion of total cases occurring in boys?
Answer: The proportion of cases occurring in boys is equal to the number of cases in boys divided by the
total number of cases (43/57). This equals 75.4%.
12. What is the proportion of total cases occurring in students who live in dormitories?
Answer: The proportion of cases occurring in dormitory residents is equal to the number of cases in
residents divided by the total number of cases (52/57). This equals 91.2%.
13. Which proportion is more informative for the purpose of the outbreak investigation?
