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Science Olympiad » Disease Detectives Event » National Event Exercises
Answer Key: Gastrointestinal Illness Among Students

Problem 1: An Outbreak of Gastrointestinal Illness Among Students

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On the basis of the information in the newspaper article and the memorandum, answer the following questions:

1. (3 points)In the space provided, give at least three reasons why the problem of illness among students at Putz Elementary School should be investigated?

Possible points include

  • Significant morbidity among young students
  • Possibility of further illness, and need to determine source of illness
  • Recommendations for future control and prevention
  • Legal liability

2. (3 points) In the space provided, indicate whether this problem is consistent with the definition of an outbreak. If so, why? If not, why not?

The student should demonstrate an understanding of the concept of an outbreak, which is the occurrence of more cases of disease or other health problem than would normally be expected for a given time or place.

Winning team's answer: "Yes, because an outbreak is a larger number of cases than expected in a given area. Though the expected number of cases is unknown, if these cases of illness attracted the attention of the local newspaper it is probably an unusually large number in this area."

3. Use the information and data in the memorandum describing the investigation to determine which consumed item(s) are most likely to have been associated with risk of illness. Show your work on the table above. Then answer the following questions in the space provided.

A) (1 point) Which food/beverage item(s) are most likely to have been associated with risk of illness?


B) (9 points) Explain how you reached your conclusion.

By comparing food-specific attack rates.

Winning team's answer: "Large numbers of students ate the burritos. Of these, a majority became ill, while only a small number of those who did not eat the burritos became ill. The relative risk is 4.5, considerably larger than any other relative risk. Some other attack rates were higher, but few ate those foods and thus they are not likely to be the source of infection."

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


D) (1 point) Name the risk estimate you calculated.

Relative risk

4. (2 points) Why did the investigators interview fifth graders instead of first or second graders? What might the effect have been if they had interviewed second graders?

To increase the chance of having more accurate information. For the really informed competitor: to minimize recall bias.

5. The figure below is an "epi curve" based on information from students in a middle school in North Dakota believed to have been affected by the same problem. Following the figure is a table listing the usual times from exposure to onset of symptoms for selected agents that cause acute gastroenteritis. Use the information in the figure and the table to answer parts A) and B) below.

A) (1 point) Give the term Disease Detectives use to refer to the time from exposure to onset of symptoms.

Incubation period

B) (3 points) Which of the agents in the table above most likely caused the illness in the North Dakota students? Explain how you selected this cause.

Scombroid toxin. Student should indicate analysis of data provided on incubation periods for the agents in the table along with data on onset of symptoms during the outbreak.

Winning team's answer: "Scombroid toxin. According to data, students experienced symptoms .5 hours after exposure. The scombroid toxin causes onset of symptoms to occur in less than one hour. A larger number of people (according to epi curve) experienced symptoms in 1 hour or less after lunch."

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Problem II: Tobacco Use by Middle School and High School Students

1.  A) (3 points) Do the results from this survey represent tobacco use practices among all young people of middle and/or high school age in Florida? Why or why not?

No. Points that students could discuss include response rate, validity of self-reported data, school attendance, generalizability.

Winning team's answer: "No, because some students chose not to respond and may have done so because they did not want anyone to know that they did smoke. Thus, prevalence may be higher amongst the nonrespondents. In addition, only the high school table is provided; rates are likely different at the middle schools level. Other school districts may also have had different rates but were not surveyed. The same is true for classrooms."

B)(3 points) Do the results from this survey represent tobacco use practices among all young people of middle and/or high school age in the United States? Why or why not?

No. The student should discuss the problem of generalizing data from one small section of one state to the entire country.

Winning team's answer: "No, only part of Florida is represented. Different regions of the country may have different rates, depending on socioeconomic status, racial composition, and outside factors."

C)(4 points) Are there any types of students or schools to which data from this survey cannot be generalized? Explain your answer.

Yes. Points include differences between types of schools (e.g., public vs. private), differences in socioeconomic and racial composition between schools, and differences based on age and grade level.

2.This survey examined the prevalence of cigarette, cigar, and smokeless tobacco use by students. Using the data in the table, answer parts A), B), and C) below.

A)(1 point) In this context, what is "prevalence"?

The frequency of tobacco use by these students at a single point time.

B)(2 points) For what tobacco product(s) is the gender difference greatest?

Smokeless tobacco

C) (2 points) For what tobacco product(s) is the race/ethnicity difference greatest?

Cigarettes and smokeless tobacco.

Winning team's answer: " Between non-Hispanic whites and non-Hispanic blacks, as well as between non-Hispanic blacks and Hispanics, cigarettes have the greatest ethnicity difference. Between non-Hispanic whites and Hispanics, smokeless tobacco has the greatest ethnic difference."

3. (3 points) List at least three possible risk factors for tobacco use and/or hypotheses that may explain the differences among racial/ethnic groups that you selected in question 2 (C).

Answers could include 1) having a family member who uses tobacco; 2) living in neighborhood where tobacco ads are featured prominently on billboards; 3) frequently attending sports events where products promoting tobacco use are given away; 4) being a member of a sports team where healthy behaviors are encouraged.

Winning team's answer:
"Risk factors:  1) Socioeconomic status  2) Exposure at home  3) Availability
Hypotheses:  1) Certain races have a socioeconomic background that predisposes them to smoking.  2) Certain races are exposed to parents or other family members who smoke more often than other races.  3) Certain races can more easily acquire tobacco products than others."

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This page last reviewed August 27, 2004

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