NR 503 EPIDEMIOLOGY WEEK 8 FINAL EXAM /
NR503 EPIDEMIOLOGY WEEK 8 FINAL EXAM
1. Which of the following is a condition which may occur during the
incubation period?
a. Onset of clinical illness
b. Receipt of infection
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.
2. Chicken pox is a highly communicable disease. It may be transmitted by
direct contact with a person infected with the varicella-zoster virus (VZV).
The typical incubation time is between 10 to 20 days. A boy started school 2
weeks after showing symptoms of chicken pox including mild fever, skin
rash, & fluid-filled blisters. One month after the boy returned to school, none
of his classmates had been infected by VZV. The main reason was:
a. Herd immunity
b. All had been immunized prior to the school year
c. Contact was after infectious period
d. Subclinical infections were not yet detected
e. Disease was endemic in the class
Rationale: The disease is spread by contact with an infected individual who can
transmit the agent (VZV) to immunologically naive persons during the incubation
period & for several days after onset of clinical illness. Since the boy started school
14 days after showing signs consistent with chicken pox, it is most likely that he
was no longer infectious.
3. Which of the following is characteristic of a single-exposure, common-
vehicle outbreak?
a. Long latency period before many illnesses develop
, b. There is an exponential increase in secondary cases following initial
exposures
c. Cases include only those who have been exposed to sick persons
d. The epidemic curve has a normal distribution when plotted
against the logarithm of time
e. Wide range in incubation times for sick individuals
Rationale: Single-exposure, common-vehicle outbreaks involve a sudden, rapid
increase in cases of disease that are limited to persons who share a common
exposure. Additionally, few secondary cases develop among persons exposed to
primary cases. A histogram of the outbreak can plot the number of cases by time of
disease onset. In single-exposure, common-vehicle outbreaks, a log transformation
of the time of disease onset will often take on the characteristic shape of a normal
distribution (i.e., a bell curve) with the median incubation time found at the peak of
the curve.
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.
NR503 EPIDEMIOLOGY WEEK 8 FINAL EXAM
1. Which of the following is a condition which may occur during the
incubation period?
a. Onset of clinical illness
b. Receipt of infection
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.
2. Chicken pox is a highly communicable disease. It may be transmitted by
direct contact with a person infected with the varicella-zoster virus (VZV).
The typical incubation time is between 10 to 20 days. A boy started school 2
weeks after showing symptoms of chicken pox including mild fever, skin
rash, & fluid-filled blisters. One month after the boy returned to school, none
of his classmates had been infected by VZV. The main reason was:
a. Herd immunity
b. All had been immunized prior to the school year
c. Contact was after infectious period
d. Subclinical infections were not yet detected
e. Disease was endemic in the class
Rationale: The disease is spread by contact with an infected individual who can
transmit the agent (VZV) to immunologically naive persons during the incubation
period & for several days after onset of clinical illness. Since the boy started school
14 days after showing signs consistent with chicken pox, it is most likely that he
was no longer infectious.
3. Which of the following is characteristic of a single-exposure, common-
vehicle outbreak?
a. Long latency period before many illnesses develop
, b. There is an exponential increase in secondary cases following initial
exposures
c. Cases include only those who have been exposed to sick persons
d. The epidemic curve has a normal distribution when plotted
against the logarithm of time
e. Wide range in incubation times for sick individuals
Rationale: Single-exposure, common-vehicle outbreaks involve a sudden, rapid
increase in cases of disease that are limited to persons who share a common
exposure. Additionally, few secondary cases develop among persons exposed to
primary cases. A histogram of the outbreak can plot the number of cases by time of
disease onset. In single-exposure, common-vehicle outbreaks, a log transformation
of the time of disease onset will often take on the characteristic shape of a normal
distribution (i.e., a bell curve) with the median incubation time found at the peak of
the curve.
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.
