Final Study Guide

Chapters 2-4

Which of the following is a condition which may occur during the incubation period?

Transmission of infection

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:

Contact was after infectious period

The ability of a single person to remain free of clinical illness following exposure to an infectious agent

is known as:

Immunity

Which of the following is characteristic of a single-exposure, common-vehicle outbreak?

The epidemic curve has a normal distribution when plotted against the logarithm of

time

What is the diarrhea attack rate in persons who ate both ice cream and pizza?

39/52

What is the overall attack rate in persons who did not eat ice cream?

33%

 1 / 4

Which of the food items (or combination of items) is most likely to be the infective item(s)?

Ice cream only

Which of the following reasons can explain why a person who did not consume the infective food item

got sick?

 They were directly exposed to persons who did eat the infective food item

 Diarrhea is a general symptom consistent with a number of illnesses

 There may have been an inaccurate recall of which foods were eaten (all of the

above)

An outbreak of gastroenteritis occurred at a boarding school with a student enrollment of 846. Fiftyseven students reported symptoms including vomiting, diarrhea, nausea, and low-grade fever

between 10 p.m. on September 24 and 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 and the number reporting illnesses consistent with the described symptoms and

onset time. Calculate the attack rate among all students at the boarding school.

The answer is found by dividing the total number of cases (57) by the total number of students (846).

This equals 6.7%.

An outbreak of gastroenteritis occurred at a boarding school with a student enrollment of 846. Fiftyseven students reported symptoms including vomiting, diarrhea, nausea, and low-grade fever

between 10 p.m. on September 24 and 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 and the number reporting illnesses consistent with the described symptoms and

onset time. Calculate the attack rates for boys and girls separately.

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%.

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%.

An outbreak of gastroenteritis occurred at a boarding school with a student enrollment of 846. Fiftyseven students reported symptoms including vomiting, diarrhea, nausea, and low-grade fever

between 10 p.m. on September 24 and 8 p.m. on September 25. The ill students lived in dormitories

 2 / 4

that housed 723 of the students. The table below provides information on the number of students per

type of residence and the number reporting illnesses consistent with the described symptoms and

onset time. What is the proportion of total cases occurring in boys?

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%.

An outbreak of gastroenteritis occurred at a boarding school with a student enrollment of 846. Fiftyseven students reported symptoms including vomiting, diarrhea, nausea, and low-grade fever

between 10 p.m. on September 24 and 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 and the number reporting illnesses consistent with the described symptoms and

onset time. What is the proportion of total cases occurring in students who live in dormitories?

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%.

An outbreak of gastroenteritis occurred at a boarding school with a student enrollment of 846. Fiftyseven students reported symptoms including vomiting, diarrhea, nausea, and low-grade fever

between 10 p.m. on September 24 and 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 and the number reporting illnesses consistent with the described symptoms and

onset time. Which proportion is more informative for the purpose of the outbreak investigation?

Both proportions are useful. Dormitory residents account for over 90% of the cases indicating an

outbreak of an infectious agent that was transmitted at the school. Furthermore, over 75% of the cases

were boys indicating that the responsible agent was more likely to have been transmitted in the boys’

dormitory.

A group of researchers are interested in conducting a clinical trial to determine whether a new

cholesterol-lowering agent was useful in preventing coronary heart disease (CHD). They identified

12,327 potential participants for the trial. At the initial clinical exam, 309 were discovered to have

CHD. The remaining subjects entered the trial and were divided equally into the treatment and

placebo groups. Of those in the treatment group, 505 developed CHD after 5 years of follow-up while

477 developed CHD during the same period in the placebo group. What was the prevalence of CHD at

the initial exam?

The prevalence of CHD at the initial exam was 309 cases of CHD divided by 12,327 participants. This

equals a prevalence of 25.1 cases of CHD per 1,000 persons.

A group of researchers are interested in conducting a clinical trial to determine whether a new

cholesterol-lowering agent was useful in preventing coronary heart disease (CHD). They identified

12,327 potential participants for the trial. At the initial clinical exam, 309 were discovered to have

CHD. The remaining subjects entered the trial and were divided equally into the treatment and

placebo groups. Of those in the treatment group, 505 developed CHD after 5 years of follow-up while

477 developed CHD during the same period in the placebo group. What was the incidence of CHD

during the 5-year study?

 3 / 4

The incidence rate reflects the number of new cases developing in the population at risk. Since prevalent

CHD cases were excluded from the study, the population at risk was 12,018 (12,327 persons less 309

cases of CHD). During the 5-year study period, 982 incident cases of CHD developed. This equals an

incidence rate of 81.7 cases of CHD per 1,000 persons.

Which of the following are examples of a population prevalence rate?

The number of persons with hypertension per 100,000 population

What would be the effect on age-specific incidence rates of uterine cancer if women with

hysterectomies were excluded from the denominator of incidence calculations assuming that most

women who have had hysterectomies are older than 50 years of age.

Rates would increase in women older than 50 years of age but may decrease in younger

women as they get older.

A survey was conducted among 1,000 randomly sampled adult males in the United States in 2005. The

results from this survey are shown below.

The researchers stated that there was a doubling of risk of hypertension in each age group younger

than 60 years of age. You conclude that the researchers’ interpretation:

Is incorrect because prevalence rates are estimated

Powered by qwivy(www.qwivy.org)

 4 / 4