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Science Olympiad » Disease Detectives Event » National Event Exercises
Problem: Febrile and Respiratory Illness


Problem I: An Outbreak of Febrile and Respiratory Illness Among Residents of Singapore and Malaysia 
(Recommended time: 35 minutes)


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Answer Key

From In early 1999, public health officials in Malaysia and Singapore were notified of people with fever and neurological illnesses (problems affecting the nervous system). In this Science Olympiad Event, you will be given information used by the Disease Detectives in those two countries and other experts to investigate this problem and address it. Begin by reading the coverage of this outbreak in CDC’s publication the Morbidity and Mortality Weekly Report (MMWR) and the letter of invitation to assist in the investigation from the Singapore Ministry of Health, on the next page. To understand this report, you need to know that encephalitis is a severe syndrome resulting from inflammation of the brain and is often characterized by fever, headache, other serious brain-related problems (e.g., seizures and coma), and muscle aches. Many different infectious agents and some non-infectious agents cause this syndrome. The infectious agents include viruses, bacteria, and fungi; non-infectious agents include toxins. One well-recognized cause of encephalitis in that region of the world is Japanese encephalitis (JE), a mosquito-borne viral infection.

Outbreak of Hendra-Like Virus Malaysia and Singapore, 1998-1999
Morbidity and Mortality Weekly Report. April 09, 1999. 48(13):265-269.

Letter of Invitation to Assist with Investigation:

MH 34:27/1 Vol 2

31 March 1999

His Excellency Steven J. Green
Ambassador Extraordinary & Plenipotentiary
Embassy of the United States of America

Your Excellency

1    Singapore is currently having an outbreat of viral infection due to the virus among abattoir workers.

2    The Ministry of Health, Singapore has been collaborating with the US Centers for Disease Control & Prevention (CDC), Atlanta, which has helped us in arriving at the diagnosis of the affected patients. We would like to invite the experts from CDC to help us carry out epidemiological investigation on this outbreak. Dr Brian Mahy, Director, Division of Viral & Rickettsial Diseases, CDC, Atlanta, has informed us that the CDC would be able to send two epidemiologists to work with the Ministry.

3     Your assistance to facilitate the visit of the epidemiologists from the CDC would be much appreciated.

4     Thank you.

Yours Sincerely

 

Dr CHEN AI JU
DIRECTOR OF MEDICAL SERVICES
MINISTRY OF HEALTH

The following graph (Figure 1) shows the number of new encephalitis cases reported by week of onset in multiple states in Malaysia from October 1998 through early April 1999.

Figure 1. Number of cases of Hendra-like virus infection, by week of illness onset Perak, Negri Sembilan, and Selangor states, Malaysia 19981999

Figure, number of cases of Hendra-like virus infection, by week of illness onset.  Perak, Negri Sembilan, and Selangor states, Malaysia 1998-1999.  Up to 50 cases in 1999 for Negri Sembilan.

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 possible explanations for this increase.

1)  

 

2) 

 

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

1) 

 

2) 

 

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?

 

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

 

Based on this information, the preliminary assessment was that this was an outbreak of JE.


5. (3 points) Give three examples of interventions that could be used to control JE.

1) 

 

2)

 

3)

 

6. (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.
 

1)

 

2)

 

3)

 

4)

 

The Disease Detectives used measures designed 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 possible explanations for these findings.

1)

 

2)

 

Electron microscopy and other laboratory tests revealed that these cases were caused, not by JE, but by a newly recognized virus (i.e., a novel paramyxovirus) not related to JE. As part of the process of differentiating between different disease agents, disease detectives use the method of descriptive epidemiology.

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)

 

2)

 

3)

 

Characteristic

Met case definition

Did not meet case definition

Sex    
Male 36 55
Female 12 52
Lived on a farm?    
Yes 39 86
No 9 21
Occupation?    
Pig farm owner/worker 40 71
Other 8 36
Close contact with pigs?*    
Yes 37 38
No 6 38

*This category includes cleaning pens, washing or feeding pigs, injecting or medicating pigs, assisting in breeding or birthing of pigs, handling dead pigs. Numbers in this category may differ because it included only those people who worked on a pig farm.

11. (11 points) Use the information/data above from the study to determine which characteristic(s) was(were) most important in helping to explain this outbreak. Then answer the following questions in the space provided.

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

 

B. Explain how you reached your conclusion. (8 points total [1 point for each correct calculation; 4 points for the correct explanation])

 

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. (2 points) Consider again the data from the study. 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 that characteristic. Speculate on different reasons for this finding.

 

13. (8 points) In investigations such as this, disease detectives draw conclusions about cause-and-effect relationships based on several criteria. List four of these criteria. For each criterion that you list, indicate whether and how the criterion was addressed by the information presented in this Science Olympiad problem.

 

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.

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Problem II: Physical Inactivity and Perceived Neighborhood Safety
(recommended time: 15 minutes)

Most public health surveillance systems monitor the occurrence of illness among defined groups of people. The Behavioral Risk Factor Surveillance System (BRFSS) monitors behaviors or activities such as smoking or exercise frequency, which place people at risk for illness rather than monitoring illness itself. A sampling scheme is used to select participants representative of defined populations (e.g., Washington State). These individuals are contacted by telephone and asked questions concerning behaviors that may put them at risk for various chronic illnesses, injuries, and infectious diseases. Several states have included questions on physical activity and perceived safety of neighborhoods on their surveys.

1. (5 points)

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

 

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

1)  

 

2)   

 

3)  

 

Table 1 below includes information on physical inactivity levels and perceived neighborhood safety from 12,767 people in Maryland, Montana, Ohio, Pennsylvania, and Virginia. Respondents were considered to be physically inactive if they reported no physical activity or exercise in the previous month. They were also asked "How safe from crime do you consider your neighborhood to be?" - possible responses included "extremely safe," "quite safe," "slightly safe," or "not at all safe."

2. (1 point) Define prevalence as used in Table I.

 

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?

 

4. (2 points) 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?

 

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

1) 

 

2)

 

TABLE 1. Prevalence of physical inactivity among people aged >18 years, by selected characteristics and perceived neighborhood safety -- Maryland, Montana, Ohio, Pennsylvania, and Virginia, Behavioral Risk Factor Surveillance System, 1996

Characteristic Total* Extremely
safe (%)
Quite safe (%) Slightly
safe (%)
Not at all safe (%)
Age (yrs)          
18-64 2898 30.5 29.1 35.1  39.3
>65  1069 38.6 40.9 45.0 63.1
Sex          
Men 1496 30.7 28.3 34.2 36.7
Women 2471 33.8 33.8 38.5 47.2
Race/Ethnicity          
White 3188 32.4 30.3 33.1 40.8
Other 779 29.9 36.8 45.1 44.6
Education level          
<12 years 2451 41.7 40.3 44.8 51.3
>12 years 1516 23.0 22.4 25.4 24.5
Annual income          
<$20,000 938 43.8 42.9 42.5 44.0
>$20,000 2269 30.7 28.6 34.4 39.8

*n=3967; numbers may not add to total because of missing data.

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This page last reviewed August 27, 2004

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