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Problem facing the Disease Detectives:
From October 1997 through October 1998, 16 outbreaks of acute gastrointestinal illness (illness involving portions of the gastrointestinal tract, including the stomach, and small and large intestines) occurred in seven states, Florida, Georgia, Illinois, Indiana, Kansas, North Dakota, and Pennsylvania. All but one outbreak occurred in schools, and most of the approximately 1,700 people affected were children. The Disease Detectives investigating this problem included epidemiologists, physicians, food safety experts, laboratory specialists, and other scientists.
Before attempting to answer questions faced by the Disease Detectives, please examine the newspaper article and the memorandum below for additional background information and details critical to solving the problem. The newspaper article was published in a North Dakota paper and describes the occurrence of this problem in a middle school in one community in that state. The memorandum is adapted from a summary of a health department investigation of a related outbreak in an elementary school in Georgia:
Home Sick: Officials still looking into illnesses*
State health department officials will try to determine what caused several Belcourt students and school staff members to get sick last week.
Last Wednesday, around 160 students and about a dozen school employees got sick at school. Most of the affected students were from the Turtle Mountain Middle School.
Dr. Richard Larson, medical director of the Quentin N. Burdick Memorial Health Care Facility, said they believe it was food poisoning but still were not completely sure.
The menu last Wednesday at Turtle Mountain schools was a breakfast of hot cereal and fresh fruit. The lunch menu consisted of burritos, Mexican rice, carrot sticks, peaches and taco sauce.
Students and staff who became ill were asked to fill out a questionnaire, Larson said. Questions on the document include what time they ate and when their symptoms started. Larson said the health department will analyze the data in Bismarck to try [to] determine a cause for the illnesses.
The 160 students from kindergarten through high school and staff began complaining of headaches, abdominal cramps and nausea early Wednesday afternoon. Forty-one of the students were taken to the hospital for treatment but not admitted, Larson said.
Most of the students who were sick on Wednesday returned to school on Thursday.
(Adapted from the original)
MEMORANDUM
TO:
Dr. Stancil
Director,
Health District 2-0
FROM:
Dr. Blake
Chief,
Epidemiology Section
Georgia
Department of Human Resources
SUBJECT: Outbreak of Nausea and Vomiting at Putz Elementary School, March 23, 1998
On Monday, March 23, 1998, teachers at Putz Elementary School in Hall County, Georgia, noted that many pupils became ill with nausea and vomiting during and shortly after lunch. The school administrators suspected food poisoning, and at about 1:30, the school dietician, Mr. Wholesome, called the Hall County health department and spoke with the local Disease Detective, Mr. Sleuth, who is an environmental health specialist. Mr. Sleuth arrived at the school at about 2:00 p.m. and immediately began an investigation. Putz Elementary School is in a rural area, serves primarily a lower socioeconomic population, and has approximately 600 pupils in 28 classes, kindergarten through fifth grade.
Mr Sleuth interviewed the school principal and four students and discovered that for these students, illness occurred less than an hour after eating. Based on this preliminary information, Mr. Sleuth developed a questionnaire and on March 24 administered this to all fifth graders. The questionnaire asked for identifying data, symptoms, time of onset of illness, and foods eaten for lunch on March 23. Further data collection included interviews of all students to determine illness.
On March 23, Mr. Sleuth collected vomitus samples from five students and samples of food from the trash for laboratory analysis. He interviewed kitchen staff members about food handling procedures and the sources of food served that day. The kitchen was inspected as well. Mr. Smith sent the food and vomitus samples to Ms. Beaker at the Georgia Public Health Laboratory. Ms. Beaker tested these materials for several different organisms that commonly cause food poisoning.
Of all students interviewed, 452 provided information considered reliable about both illness and foods eaten. Of these, 155 (34%) had become ill following the lunch on March 23. Symptoms reported by fifth graders were nausea (89%), headache (65%), abdominal pain (53%), vomiting (29%), and diarrhea (17%). The duration of illness for fifth graders ranged from 10 minutes to 8 hours with a median of 4.5 hours.
The children had a choice of eight food and beverage items at lunch. Information on fifth graders who ate the food and beverage items and on those who did not is summarized in the table below.
Table. Foods eaten and beverage consumed at lunch by fifth grade classes Putz Elementary School, Gainesville, Georgia, March 23, 1998
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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.
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?
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 consumed item(s) are most likely to have been associated with risk of illness?
B) (9 points) Explain how you reached your conclusion.
C) (1 point) Name the type of study design you used.
D) (1 point) Name the risk estimate you calculated.
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?
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.
Table of agents causing acute gastroenteritis
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A) (1 point) Give the term Disease Detectives use to refer to the time from exposure to onset of symptoms.
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.
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*
Smoked cigarettes on >=1 of the 30 days preceding the survey.
+ Smoked cigars on >=1 of the 30 days preceding the survey.
& Used smokeless tobacco on >=1 of the 30 days preceding
the survey.
@ Confidence interval.
1.
A) (3 points) Do the survey results represent tobacco use practices among all young people of middle and/or high school age in Florida? Why or why not?
B) (3 points) Do the survey results represent tobacco use practices among all young people of middle and/or high school age in the United States? Why or why not?
C) (4 points) Are there any types of students or schools to which data from this survey cannot be generalized? Explain your answer.
2. This survey examined the prevalence of cigarette, cigar, and smokeless tobacco use by students. Using data from the table, answer parts A), B), and C).
A) (1 point) In this context, what is "prevalence"?
B) (2 points) For what tobacco product(s) is the gender difference greatest?
C) (2 points) For what tobacco product(s) is the race/ethnicity difference greatest?
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).
