1. ( 1 point) What is the term used by Disease Detectives to refer to this type of bar graph?
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.
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
3. (2 points) Give two explanations for the decline in reported cases by week, beginning in late March.
Depletion of susceptible people
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?
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?
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.
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.
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)
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.
Collection of the wrong specimens
Inappropriate collection, transport, or testing
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.)
Time: date of onset, date of diagnosis, date of report to health authority, date of hypothesized exposure.
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)
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 AnswerSuggests 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)
Closed contact with pigs
B. Explain how you reached your conclusion. (1 point for each correct calculation; 4 points for the correct explanation)
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)
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)
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.
The respondent could not recall the exposures;
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)
Strength of the association: yes
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.
This page last reviewed August 27, 2004
United States Department of Health Human Services