1
, c. Signs & symptoms of disease
d. Transmission of infection
e. Isolation of disease carrier through quarantine
Rationale: The incubation period is defined as the interval from receipt of infection to the time
of onset of clinical illness. Accordingly, individuals may transmit infectious agents during the
incubation period as they show no signs of disease that would enable the isolation of sick
individuals by quarantine.
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.
, c. Signs & symptoms of disease
d. Transmission of infection
e. Isolation of disease carrier through quarantine
Rationale: The incubation period is defined as the interval from receipt of infection to the time
of onset of clinical illness. Accordingly, individuals may transmit infectious agents during the
incubation period as they show no signs of disease that would enable the isolation of sick
individuals by quarantine.
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.
