NR 503 Epidemiology midterm questions and answers

NR503 Epidemiology midterm questions:

1. Prevalence Rate Calculation:
   • Question: The population of a city on February 15, 2005, was 36,600. During the period between January 1 and April 1, 2005, 2,200 new cases of influenza occurred in the city. Of these cases, 775 persons were ill with influenza according to surveillance reports on April 1, 2005. The prevalence rate of active influenza as of April 1, 2005, was:
   • Answer: 20 per 1,000 population
   • Explanation: The prevalence rate is calculated by dividing the number of active cases (775) by the total population (36,600) and then multiplying by 1,000. Thus, (775 / 36,600) * 1,000 = 21.2 per 1,000, rounded to 20 per 1,000.
2. Monthly Incidence Rate Calculation:
   • Question: The population of a city on February 15, 2005, was 36,600. During the period between January 1 and April 1, 2005, 2,200 new cases of influenza occurred in the city. The monthly incidence rate of active cases of influenza for the 3-month period was:
   • Answer: 20 per 1,000 population
   • Explanation: The monthly incidence rate is calculated by dividing the number of new cases (2,200) by the population (36,600) and then dividing by 3 months, followed by multiplying by 1,000. Thus, (2,200 / 36,600) / 3 * 1,000 = 20 per 1,000.
3. Effect of Excluding Women with Hysterectomies:
   • Question: 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?
   • Answer: Rates would increase in women older than 50 years of age but may decrease in younger women as they get older.
   • Explanation: Excluding women with hysterectomies (who are mostly older) from the denominator will increase the incidence rates in the older age group because the denominator is reduced, and this will likely decrease rates in younger women who remain in the denominator.
4. Immunity Definition:
   • Question: The ability of a single person to remain free of clinical illness following exposure to an infectious agent is known as:
   • Answer: Immunity
   • Explanation: Immunity refers to the body’s ability to resist or avoid illness after exposure to a pathogen.
5. Reasons for Illness Despite Non-consumption:
   • Question: Which of the following reasons can explain why a person who did not consume the infective food item got sick?
   • Answer: All of the above
   • Explanation: Various reasons such as cross-contamination, secondary transmission, or other exposures can explain why someone who did not consume the infective item may still get sick.
6. Most Likely Infective Item:
   • Question: Which of the food items (or combination of items) is most likely to be the infective item(s)?
   • Answer: Ice cream only
   • Explanation: Ice cream may be identified as the source based on contamination patterns or epidemiological investigations.
7. Case-Fatality Rate in Communities:
   • Question: The case-fatality rate associated with plague is lowest in which community?
   • Answer: Community C
   • Explanation: Case-fatality rates are typically assessed by comparing the number of deaths to the number of cases in different communities.
8. Duration of Disease Interpretation:
   • Question: The incidence and prevalence rates of a chronic childhood illness for a specific community are given below. The duration of disease is becoming longer.
   • Answer: The duration of disease is becoming longer.
   • Explanation: If prevalence rates increase relative to incidence rates, it suggests that the duration of the illness is extending.
9. Mortality Rates from Measles:
   • Question: The following table gives the mean annual age-specific mortality rates from measles during the first 25 years of life in successive 5-year periods. Children ages 5 to 9 had the highest rate of death in all periods.
   • Answer: Children ages 5 to 9 had the highest rate of death in all periods.
   • Explanation: The highest mortality rates are observed in the 5-9 age group across all periods.
10. Statements About TB Mortality:
    • Question: In a country with a population of 16 million people, 175,000 deaths occurred during the year ending December 31, 2005. These included 45,000 deaths from tuberculosis (TB) in 135,000 persons who were sick with TB. Assume that the population remained constant throughout the year. Not all 135,000 cases of TB were contracted during 2005. Which of the following statements is true?
    • Answer: None of the above
    • Explanation: The specific statements related to TB mortality are not true given the available data.
11. Motor Vehicle Accident Law Impact:
    • Question: 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. Based on the information, the increased risk of death due to MVAs after the law was passed is:
    • Answer: Correct, because both the total and the age-adjusted mortality rates are higher in 2005 than in 2000.
    • Explanation: The higher mortality rates post-law indicate an overall increased risk despite safety measures.
12. Advantage of Active Surveillance:
    • Question: Which of the following is an advantage of active surveillance?
    • Answer: More accurate due to reduced reporting burden for health care providers
    • Explanation: Active surveillance involves proactive data collection, which can lead to more accurate data and reduced burden on providers.
13. Disease Detection and Duration:
    • Question: A disease has an incidence of 10 per 1,000 persons per year, and 80% of those affected will die within 1 year. A lab test in 2000 identified 90% of cases an average of 6 months prior to symptom onset. Which statement is true concerning the duration of the disease after the development of the lab test?
    • Answer: Mean duration of a case of the disease is longer in 2000
    • Explanation: The earlier detection extends the duration of the disease in the population, even if prognosis remains unchanged.
14. Overall Attack Rate Calculation:
    • Question: What is the overall attack rate in persons who did not eat ice cream?
    • Answer: 33%
    • Explanation: The attack rate is calculated by the number of affected individuals who did not eat the item divided by the total number who did not eat the item, expressed as a percentage.
15. Case-Fatality Rate in Communities:
    • Question: The table describes the number of illnesses and deaths caused by plague in four communities. The case-fatality rate associated with plague is lowest in which community?
    • Answer: Community D
    • Explanation: Case-fatality rates are assessed by comparing the number of deaths to the number of cases in each community.
16. Single-Exposure Outbreak Characteristic:
    • Question: Which of the following is characteristic of a single-exposure, common-vehicle outbreak?
    • Answer: The epidemic curve has a normal distribution when plotted against the logarithm of time.
    • Explanation: Single-exposure outbreaks often show a normal distribution curve on a logarithmic scale due to the nature of the exposure.
17. Mortality Rates from Measles:
    • Question: The following table gives the mean annual age-specific mortality rates from measles during the first 25 years of life. Based on the information, the rates are:
    • Answer: 2.4 3.3 2.0 0.6 0.1
    • Explanation: These values represent the mortality rates by age group.
18. Epidemiology of Disease Before and After 2000:
    • Question: A disease has an incidence of 10 per 1,000 persons per year, and 80% of those affected will die within 1 year. In the year 2000, a lab test was developed that identified 90% of cases 6 months prior to symptom onset. Comparing the epidemiology of the disease prior to 2000 with the epidemiology in 2000, which statement is true?
    • Answer: Incidence is higher and prevalence is higher than in 1999.
    • Explanation: Earlier detection increases prevalence without changing incidence rates.
19. Prevalence of Hypertension Interpretation:
    • Question: A survey found that adults older than age 50 had a higher prevalence of hypertension. The researchers' interpretation that there was a doubling of risk is:
    • Answer: Incorrect because prevalence rates are estimated.
    • Explanation: The higher prevalence may reflect longer duration rather than an increased risk.
20. Condition During Incubation Period:
    • Question: Which of the following is a condition which may occur during the incubation period?
    • Answer: An individual may be contagious.
    • Explanation: Some diseases are contagious during the incubation period even though symptoms may not yet be evident.
21. Epidemic Curve Interpretation:
    • Question: An epidemic curve showing cases of a disease is plotted against the logarithm of time. If the curve is rectangular in shape, it indicates:
    • Answer: A common source outbreak.
    • Explanation: A rectangular curve on a logarithmic scale typically indicates a common source outbreak.
22. Food Item Linked to Hepatitis:
    • Question: If the case definition is “hepatitis A,” which food item is most likely to be linked to the outbreak?
    • Answer: Ice cream
    • Explanation: Hepatitis A outbreaks are often linked to food items like ice cream that have been contaminated.
23. Mortality Rate and Case-Fatality Rate:
    • Question: In a given year, a state had a population of 1,000,000 with 100,000 deaths including 1,000 from a particular disease. The mortality rate and case-fatality rate for the disease were:
    • Answer: Mortality rate: 0.1%; Case-fatality rate: 1.0%
    • Explanation: Mortality rate is the number of deaths from the disease divided by the total population, while case-fatality rate is the number of deaths from the disease divided by the number of cases.
24. Incidence Rate Calculation:
    • Question: If there are 500 new cases of a disease in a population of 10,000, the annual incidence rate is:
    • Answer: 5 per 100
    • Explanation: The incidence rate is calculated by dividing the number of new cases by the population and then multiplying by 100.
25. Risk of Death from Disease:
    • Question: A disease causes 10 deaths in a population of 1,000. If 100 individuals are diagnosed with the disease, the case-fatality rate is:
    • Answer: 10%
    • Explanation: The case-fatality rate is the number of deaths divided by the number of cases, expressed as a percentage.
26. Active Surveillance Advantage:
    • Question: An advantage of active surveillance is:
    • Answer: More accurate due to reduced reporting burden for health care providers
    • Explanation: Active surveillance involves proactive data collection, which can improve accuracy and ease the burden on providers.
27. Effective Interventions in Disease Prevention:
    • Question: Which type of intervention is most effective in preventing the spread of infectious diseases?
    • Answer: Vaccination programs
    • Explanation: Vaccination programs are highly effective in preventing the spread of infectious diseases.
28. Understanding Epidemic Curves:
    • Question: An epidemic curve that rises and falls rapidly indicates:
    • Answer: A common-source outbreak
    • Explanation: Rapid rise and fall in an epidemic curve are indicative of a common-source outbreak.
29. Endemic Disease Characteristics:
    • Question: An endemic disease is characterized by:
    • Answer: Consistent and predictable occurrence within a specific geographic area
    • Explanation: Endemic diseases consistently occur at expected levels in specific areas.
30. Long-Term Disease Outcome Measurement:
    • Question: Measuring long-term disease outcomes is most accurately done using:
    • Answer: Cohort studies
    • Explanation: Cohort studies are effective for tracking long-term disease outcomes.