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Answer Key: Febrile and Respiratory Illness

Problem I: An Outbreak of Febrile and Respiratory Illness Among Residents of Singapore and Malaysia

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1. ( 1 point) What is the term used by Disease Detectives to refer to this type of bar graph?

Suggested Answers
Epidemic curve
Epi curve
Incidence curve

2. ( 2 points) This bar graph (Figure 1) shows an increase in reported cases per week in Negri Sembilan beginning in February 1999. Give two explanations for this apparent increase.

Suggested Answers
Improved reporting
Increased awareness or publicity
Greater number of susceptible people
New systems in place to detect cases (increased ascertainment)
Incorrect diagnoses from health care providers
Laboratory error (pseudo outbreaks)
False positive test results
Real outbreak

3. (2 points) Give two explanations for the decline in reported cases by week, beginning in late March.

Suggested Answers
Depletion of susceptible people
Effective interventions
Decreased/delayed reporting
Natural history (disappearance of agents; vectors gone)

4. (2 points) One of the first steps used by disease detectives in an investigation like this is to confirm the existence of an outbreak.

A. What is an outbreak?

Suggested Answers
The occurrence of more cases of a particular disease than expected in a given area, or among a specific group of people, over a particular period of time.

B. What is the purpose of confirming the occurrence of an outbreak early in an investigation like this one?

Suggested Answers
To be sure you are dealing with a real problem.
To make the most efficient use of resources.
To respond to public concerns.
Based on this information, the preliminary assessment was that this was an outbreak of JE.

5. (4 points) In addition to the methods used to counter the mosquito-borne problem of JE, considering all different kinds of public health problems, list 4 specific additional strategies or methods for prevention and control of diseases and injury and specify the public health problem(s) that these methods address.

Suggested Answers
clean food
clean water
chemoprophylaxis
quarantine and isolation
legislation (e.g., seat belts)
environmental modification (give examples: install
  soft floors in nursing homes)

6. (3 points) Give three examples of interventions that could be used to control JE.

Suggested Answers
Environmental measures (e.g., pesticide spraying, larvicide application to standing water, reservoir elimination)
Education programs (e.g., avoid outside activity at dusk)
Provision and use of personal protective measures (e.g., bed nets, insect repellent)
Vaccination

The Disease Detectives used measures appropriate to control JE. However, when results of blood tests on 13 cases came back from the laboratory, 12 were negative for JE.

7. (2 points) Give two explanations for these findings.

Suggested Answers
Lab error
Collection of the wrong specimens
Inappropriate collection, transport, or testing
False negative
JE was not the agent in this outbreak
This is an outbreak of JE, but these cases are not part of the outbreak

8. (6 points) What are the three basic categories of information regarding cases that disease detectives use when applying principles of descriptive epidemiology? Name the three categories and give specific examples of these categories for an outbreak investigation. (1 point for each principle, 1 point for each set of specific examples.)

Suggested Answers
Time: date of onset, date of diagnosis, date of   report to health authority, date of hypothesized exposure.
Place: place of residence, place of work, place of   social activity, room in a building, travel.
Person: age, race, sex, occupation, behavior.

9. (3 points) A. On the basis of your analysis of these data, indicate which of the two outbreaks (A or B) was more likely to have resulted from mosquito-borne transmission? (1 point)

B. Explain your answer. (2 points)

Suggested Answers
Outbreak A: Because cases are distributed more evenly across all age groups.

Outbreak B: Because young people are more likely to be protected (infants not outside, maternally-acquired passive immunity); older people are more likely to be immune or more likely to use protective measures or avoid contact.

10. (2 points) A. What possible conclusion does this information suggest? (1 point)

B. Why would the disease detectives be reluctant to reach this conclusion at this point in the investigation. (1 point)

Suggested Answer
Suggests residence or employment on farms may be a risk factor for illness (1 point). But they don't know how many well people (controls) also live/work on pig farms.

11. (11 points) Use the information/data above from the survey to determine which characteristic(s) were most important in helping to explain this outbreak. Show your work beside the table on page 8. Then answer the following questions in the space provided.

A. Which characteristic(s) was/were most important? (1 point)

Suggested Answer
Closed contact with pigs

B. Explain how you reached your conclusion. (1 point for each correct calculation; 4 points for the correct explanation)

Suggested Answer
Calculate the odds that each characteristics is associated with developing disease (odds ratio).  The exposure with the highest odds ratio is the one most likely to be related to becoming ill.

C. Name the type of study design the disease detectives used. (1 point)

Suggested Answer
Case-Control Study

D. What is the term that disease detectives use for the risk estimate you calculated, and what is it's largest value for this study? (1 point)

Suggested Answer
Odds Ratio; 6.20

12. (1 points) Consider again the data from the survey. For the characteristic you determined to be most important as a possible cause of the outbreak (question11), note that some ill people reported not having the characteristic. Speculate on different reasons for this finding.

Suggested Answers
The respondent could not recall the exposures;
Proxy for respondent could not provide accurate   exposure information;
The respondent deliberately concealed information on exposure to pigs (e.g., religious prohibitions)
There are unidentified risk exposures;
These are cases of something else.

13. (8 points) In investigations such as this, disease detectives draw conclusions about cause-and-effect relationships based on several factors. List four of these factors. Which of these was addressed by your analysis. (1 point for each tenet and 1 point for each explanation)

Suggested Answers
Strength of the association: yes
Temporality: depends on how the question was   asked, probably yes
Dose-response: no
Consistency/coherence: no
Biologic plausibility: no
1-1 relationship: no

14. (4 points) The outbreak in Malaysia was caused by what has been termed an "emerging infectious disease." An emerging infectious disease is one of infectious origin for which incidence in people has increased in the past 20 years or threatens to increase in the near future. Factors that influence emerging infectious diseases are dynamic. Name four of these factors.

Suggested Answers
Human demographics
Human behavior
Technology and industry
Economic development and land use
International travel and commerce
Microbial adaptation and change (e.g., drug   resistance)
Breakdown of public health measures

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Problem II: Physical Inactivity and Perceived Neighborhood Safety

1. (5 points) A. Why would public health officials be interested in this information? (2 points)

Suggested Answers
Physical activity is a good thing. Public health officials need to know what promotes or prohibits/deters physical activity.

• Give three general characteristics of people that might influence their perceptions of neighborhood safety? (1 point for each)

Suggested Answers
Age
Ethnicity
Sex
Income
Marital status

2. (1 point) According to the data in Table I, what is prevalence?

Suggested Answer
The percentage of people who are physically inactive, among all people reporting a given perception of neighborhood safety. Need a numerator/denominator.

3. (1 point) Using the data in Table I, what overall conclusion can you draw about the relationship between physical inactivity and perceived neighborhood safety?

Suggested Answer
In general, levels of physical inactivity are greater in less safe neighborhoods.

4. (1 point) Examine the results for the category of educational level. What hypotheses may help to explain differences in the prevalence of inactivity as reported by people who are highly educated and by those less educated?

Suggested Answer
As the neighborhood gets less safe, highly educated people show no variation in prevalence of inactivity. These people may be more committed to exercising and may not be concerned about risk. May deny danger. Similarly, for people with less education, neighborhood safety has more relationship to physical inactivity-more concern with risk. For a given level of perceived neighborhood safety, prevalence of inactivity is almost 2-fold greater among people with less education-correlation between commitment to physical activity and education level.

5. (2 points) Suppose you are in high school at Spokane Central and have been asked by your science teacher to critique this study. List at least two limitations to this report.

Suggested Answers:

Self-reported data
Cross-sectional study
Geographical differences
Relatively small sample size
Lack of information on subgroups (e.g., "other" race)
Confounding factors.

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