1
,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.
, Question 3
The ability of a single person to remain free of clinical illness following exposure to an
infectious agent is known as:
Hygiene
Vaccination
Herd immunity
Immunity
Latency
Explanation
Immunity is the capacity of a single individual to avoid disease susceptibility when exposed to
an infectious agent. Herd immunity is a population characteristic. For certain diseases, individual
immunity can be acquired by vaccination, but this is not true for all infectious diseases.
Question 4
Which of the following is characteristic of a single-exposure, common-vehicle outbreak?
Long latency period before many illnesses develop
There is an exponential increase in secondary cases following initial exposures
Cases include only those who have been exposed to sick persons
The epidemic curve has a normal distribution when plotted against the logarithm of time
Wide range in incubation times for sick individuals
Explanation
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.
, Question 5
What is the diarrhea attack rate in persons who ate both ice cream and pizza?
39/52
21/70
39/67
51/67
none of the above
Explanation
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 and pizza. Of these 52 persons, 39 developed diarrhea.
Question 6
What is the overall attack rate in persons who did not eat ice cream?
30%
33%
35%
44%
58%
Explanation
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).
,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.
, Question 3
The ability of a single person to remain free of clinical illness following exposure to an
infectious agent is known as:
Hygiene
Vaccination
Herd immunity
Immunity
Latency
Explanation
Immunity is the capacity of a single individual to avoid disease susceptibility when exposed to
an infectious agent. Herd immunity is a population characteristic. For certain diseases, individual
immunity can be acquired by vaccination, but this is not true for all infectious diseases.
Question 4
Which of the following is characteristic of a single-exposure, common-vehicle outbreak?
Long latency period before many illnesses develop
There is an exponential increase in secondary cases following initial exposures
Cases include only those who have been exposed to sick persons
The epidemic curve has a normal distribution when plotted against the logarithm of time
Wide range in incubation times for sick individuals
Explanation
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.
, Question 5
What is the diarrhea attack rate in persons who ate both ice cream and pizza?
39/52
21/70
39/67
51/67
none of the above
Explanation
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 and pizza. Of these 52 persons, 39 developed diarrhea.
Question 6
What is the overall attack rate in persons who did not eat ice cream?
30%
33%
35%
44%
58%
Explanation
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).
