HOMEWORK 1
Section 1- Open-ended questions
1. Write down the formulae for food-specific attack rate. [2 marks]
2. Which of the food items (or combination of items) is most likely to be the
infective item(s)? Explain your answer showing calculations where necessary.
[2 marks]
3. Give some reasons that can explain why a person who did not consume the
infective food item got sick? Keep in mind that the disease being considered is
diarrhea. [2 marks]
4. An outbreak of gastroenteritis occurred at a boarding school with a student
enrollment of 846. Fifty-seven 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.
[2 marks]
5. An outbreak of gastroenteritis occurred at a boarding school with a student
enrollment of 846. Fifty-seven 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
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symptoms and onset time. What is the proportion of total cases occurring in boys?
[2 marks]
6. An outbreak of gastroenteritis occurred at a boarding school with a student
enrollment of 846. Fifty-seven 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? [2 marks]
7. 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? [2 marks]
8. In a coastal area of a country in which a tsunami struck, there were 100,000
deaths in a population of 2.4 million for the year ending December 31, 2005.
What was the all-cause crude mortality rate per 1,000 persons during 2005?
[2 marks]
9. In an industrialized nation, there were 192 deaths due to lung diseases in miners
ages 20 to 64 years. The expected number of deaths in this occupational group,
based on age-specific death rates for lung diseases in all males ages 20 to 64
years, was 238 during 1990. What was the standardized mortality ratio (SMR) for
lung diseases in miners? [2 marks]
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10. In 2001, a state enacted a law that required the use of safety seats for all children
under 7 years of age and mandatory seatbelt use for all persons. The table below
lists the number of deaths due to motor vehicle accidents (MVAs) and the total
population by age in 2000 (before the law) and in 2005 (4 years after the law was
enacted).
What is the age-specific mortality rate due to MVAs for children ages 0 to 18
years in 2000? [2 marks]
11. Is it true to say that a mortality rate is an example of an incidence rate? Explain
your answer. [2 marks]
12. Is it valid to say for a disease such as liver cancer, which is highly fatal and of
short duration, incidence rates will be equal to mortality rates? Explain your
answer. [2 marks]
13. Fill in the blanks for the following incidence density question:
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Incidence Density – Example
1
2
3
4
5
6
7
8
9
10
Jan 1 Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
0 1
2
3
4
5
6
7
8
9 10 1 1 12
Numerator = ………………
Total number of persons at risk in the beginning of the study period = ………………
Cumulative Incidence = ………………
Person-months = ………………
Incidence Density = ………………
Per year = ………………
[6 marks]
Section1 - [30 marks]
Section 2- Case study
CASE STUDY – Paralytic illness in Ababo
PART I
It is the early 1990s. The World Health Organization is planning a program for the global
eradication of polio by the year 2000. Likura, a fictitious nation in south-central Africa,
may become one of the countries selected to test the effectiveness of WHO's polio
eradication strategies. Unfortunately, little is known about polio in Likura. The Minister
of Health therefore assigned the task of assessing the polio situation to a Ministry worker
who has recently returned from an epidemiology course in Atlanta, and who is about to
become the District Health Officer in the Ababo District. The Ababo District is a
relatively poor, rural district with a single hospital and several health centers. The
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Ababo District has attempted to conduct surveillance on polio cases and deaths over the
past five years. The hospital, health centers, and all health workers are supposed to report
such cases to the District Health Officer.
Question 1: What is incidence? [2 marks]
One measure of the polio situation in a community is the prevalence of lameness in
children, since lameness is a common sequel of polio.
Question 2: What is prevalence? [2 marks]
Question 3a: What data might you use (or collect) to determine the incidence of polio in
the population? [2 marks]
Question 3b: What data might you use (or collect) to determine the prevalence of the
sequelae of polio (lameness) in the population? [2 marks]
Question 4: What are the key elements included in the definition of public health
surveillance? [2 marks]
Question 5: What is the difference between active and passive surveillance systems? Is
the Ababo surveillance system for polio passive or active? [2 marks]
PART 2
To characterize the incidence of polio over time, the new District Health Officer
tabulated the routinely collected surveillance records for the past five years. In Ababo,
the operational surveillance case definition for polio is acute onset of flaccid paralysis
plus fever. The data are shown in Table 1. The most recent census was conducted in
1986, when the population of the Ababo District was determined to be 360,000 persons.
The population in Ababo is assumed to be growing at a constant rate of 3.8% per year.
Table 1. Polio Morbidity and Mortality, Ababo District, 1986-1990
Year
Number
Number
Midyear
Incidence Mortality
of new
of deaths population rate per
rate per
cases
100,000
100, 000
1986
54
5
360,000
1987
56
7
1988
50
6
1989
68
8
1990
74
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Case –
fatality
rate (%)
Question 6a: What is a case-fatality rate? What does it measure? [2 marks]
Question 6b: Complete Table 1 by calculating the annual midyear population estimates,
polio incidence rates, disease-specific mortality rates, and case-fatality rates for each of
the past five years. [6 marks]
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Case study adopted from:
Centers for Disease Control and Prevention
Epidemiology Program Office
Case Studies in Applied Epidemiology
No. 891-903
Section 2 – [20 marks]
Total homework – [50 marks]
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