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East Carolina University *
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3011
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Health Science
Date
Feb 20, 2024
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Practice test for HLTH 4011 Introduction to Epidemiology
Measures of association
In a cohort of college freshmen, 190 of the 6,500 freshmen developed a sexually transmitted disease (STD). Use the below data to calculate the incidence rate of STDs for males and females. Express your answer per 10,000 person-months and round to the tenth decimal place. number of cases
person time
males
70
205,700
females
120
180,000
1.
What is the incidence rate of STDs among males? Express the answer per 10,000 person-
months and round to the tenth decimal place. 70 / 205,700 = 0.003403 * 10,000 = 3.4 cases per 10,000 person-months
2.
What is the incidence rate of STDs among females? Express the answer per 10,000 person-months and round to the tenth decimal place. 120 / 180,000 = 0.0006667 * 10,000 = 6.7 cases per 10,000 person months
3.
What is the incidence rate ratio comparing the incidence rate of males to females? Express the answer as a number and round to the tenth decimal place. 3.4 / 6.7 = 0.5104 = 0.5
4.
Interpret the incidence rate ratio.
The incidence rate of STDs among males was 0.5 times the rate among females. Males had lower risk of STDs than females.
5.
A case control study was conducted to examine if the use of hair dye was associated with breast cancer. Use the below data to calculate the odds ratios examining hair dye use with breast cancer. Express your answer as a number and round to the tenth decimal place. breast cancer
no breast cancer
hair dye
75
150
no hair dye
37
200
(75*200) / (150*37) = 2.7
6.
Interpret the odds ratio
Women who used hair dye had 2.7 the odds of breast cancer compared to women who did not use hair dye. Women who used hair dye had a higher odds of breast cancer compared to women who did not use hair dye. Epidemiologic Study Design
7.
A random sample of adults from Winston-Salem, NC were enrolled in a study. At baseline they answered questions about health behaviors and were followed for 20 years to see if they developed cardiovascular disease. What type of study design is this?
This is a cohort study.
8.
Researchers were interested in investigating pesticide use and kidney cancer in Wilson, NC. They identified agricultural workers who had kidney cancer. For each person with cancer, they identified a healthy neighbor of the same age and sex as the person with cancer. They interviewed both groups, those with cancer and those without cancer, about pesticide use over the past 20 years. What type of study design is this?
This is a case control study.
Surveillance
A new diagnostic test was developed to detect a new strain of flu that was circulating at ECU in November-December of 2022. The Pitt County Health Department estimated the sensitivity and
specificity of the test. Use the below table to calculate the sensitivity and specificity. Detected by diagnostic test
has the flu
does not have the flu
Has flu
120
26
Does not have flu
28
147
Total
148
173
9.
Calculate the sensitivity
. Multiply your answer by 100 to express it as a percentage and round to the tenth decimal place. Sensitivity is a/a+c
120/148 = 0.8108 * 100 = 81.1%
10. Calculate the specificity
. Multiply your answer by 100 to express it as a percentage and round to the tenth decimal place. Specificity is d/b+d
147/173 = 0.8497 * 100 = 85.0%
11. Would you recommend that the Health Department use this new diagnostic test?
a)
Yes
b)
No
The answer is a
12. Please explain your decision
Both sensitivity and specificity are above 80%. Our rule of thumb is that the tests are of high quality if both sensitivity and specificity are above 80%. 13. Sexually transmitted diseases are notifiable diseases.
a)
True
b)
False
The answer is a. Notifiable diseases are diseases that require reporting by law.
14. In this type of surveillance, health agencies contact health providers to get reports of specific diseases. Which type of surveillance method is this?
a)
Sentinel
b)
Active
c)
Passive
d)
Syndromic
The answer is b.
Outbreak investigation
15. This type of epidemic curve occurs when people are exposed over a long period of time from the same source.
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Continuous common source
North Carolina tracks the number of new HIV cases. In December 2022, the Health Department was alerted by a doctor that there may be an increase in new HIV cases, as he had seen more cases recently than usual. The Health Department decided to examine the prevalence of HIV in December 2022 and compare it to December 2021 and 2020. Number of cases
Population
December 2022
35,632 1,060,000 December 2021
44,876 1,050,000 December 2020
40,235 1,040,000 16. What is the prevalence in December 2022. Express the answer as a percent per 1,000 people.
35,632/1,060,000 = 0.03361 * 1000 = 33.6% per 1,000 people
17. What is the prevalence in December 2021. Express the answer as a percent per 1,000 people.
44,876/1,050,000 = 0.04273 * 1000 = 42.7% per 1,000 people
18. What is the prevalence in December 2020. Express the answer as a percent per 1,000 people.
40,235/1,040,000 = 0.03867 * 1000 = 38.7% per 1,000 people
19. Do you think there is an outbreak occurring in December 2022?
No, the prevalence looks similar across all the years. In fact, the prevalence is lowest for the year
2022. The doctor may have seen more cases than usual but across the state of NC the prevalence was not higher in 2022 compared to the previous years. During finals week, 25 students visited ECU Campus health with symptoms that suggested food poisoning. The Pitt County health department questioned the students about the foods they had eaten and decided students who had eaten food from the Harris Teeter were the ones experiencing the outbreak. They wanted to narrow down which foods were the cause of the outbreak. Use the below data to calculate the attack rates of eating certain foods. Ate/drank food item
Did not eat/drink food item
Risk
ratio
num of ill
people
total num
of people
attack
rate
num of
ill
people
total
num of
people
attack
rate
Pizza
10
30
12
30
Hummus
5
14
8
24
Sushi
24
30
3
30
Multiply the attack rate by 100 to express it as a percentage and round your answer to the tenth
decimal place. 20. What is the attack rate for eating pizza?
10/30 = 33.3%
21. What is the attack rate for not eating pizza?
12/30 = 40.0%
22. What is the risk ratio for eating pizza?
33.3/40 = 0.83 = 0.8
23. What is the attack rate for eating hummus?
5/14 = 35.7%
24. What is the attack rate for not eating hummus?
8/24 = 33.3%
25. What is the risk ratio for eating hummus?
35.7/33.3 = 1.07 = 1.1
26. What is the attack rate for eating sushi?
24/30 = 80%
27. What is the attack rate for not eating sushi?
3/30 = 10.0%
28. What is the risk ratio for eating sushi?
80/10= 8.0
29. What was the likely source of the outbreak?
The largest risk ratio was for sushi at 8 (the risk ratios for the other foods were much lower), therefore we think the source of the outbreak was due to contaminated sushi.
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