Question 1
Which of the following is a condition which may occur during the incubation period?
Transmission of infection
Isolation of disease carrier through quarantine
That's correct!
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.
Question 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, and fluid-filled blisters. One month after the boy
returned to school, none of his classmates had been infected by VZV. The main reason was:
Herd immunity
That's correct!
The disease is spread by contact with an infected individual who can transmit the agent
(VZV) to immunologically naive persons during the incubation period and 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.
, Question 3
The ability of a single person to remain free of clinical illness following exposure to an
infectious agent is known as:
Herd immunity
That's correct!
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?
There is an exponential increase in secondary cases following initial exposures
That's correct!
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?
,
That's correct!
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?
That's correct!
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).
Question 7
Which of the food items (or combination of items) is most likely to be the infective item(s)?
, Pizza only
Ice cream only
That's correct!
Among persons eating ice cream, over 70% developed diarrhea regardless of their pizza
consumption (39/52 and 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 and 9/30).
Question 8
Which of the following reasons can explain why a person who did not consume the
infective food item got sick?
That's correct!
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.
Which of the following is a condition which may occur during the incubation period?
Transmission of infection
Isolation of disease carrier through quarantine
That's correct!
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.
Question 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, and fluid-filled blisters. One month after the boy
returned to school, none of his classmates had been infected by VZV. The main reason was:
Herd immunity
That's correct!
The disease is spread by contact with an infected individual who can transmit the agent
(VZV) to immunologically naive persons during the incubation period and 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.
, Question 3
The ability of a single person to remain free of clinical illness following exposure to an
infectious agent is known as:
Herd immunity
That's correct!
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?
There is an exponential increase in secondary cases following initial exposures
That's correct!
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?
,
That's correct!
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?
That's correct!
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).
Question 7
Which of the food items (or combination of items) is most likely to be the infective item(s)?
, Pizza only
Ice cream only
That's correct!
Among persons eating ice cream, over 70% developed diarrhea regardless of their pizza
consumption (39/52 and 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 and 9/30).
Question 8
Which of the following reasons can explain why a person who did not consume the
infective food item got sick?
That's correct!
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.
