A local health department epidemiologist investigated an outbreak of gastrointestinal illness thought to be associated with a college cafeteria. There were many complaints about the quality of the cafeteria’s offerings, and it appeared that the student’s worst expectations were confirmed when several students visited the college’s infirmary during the middle of the night and the following day complaining of nausea, diarrhea, fever, vomiting, and cramps. The health department’s investigation revealed that 24 students had eaten in the cafeteria and the development of active symptoms ranged from 24-36 hours. A list of foods eaten, the number of persons eating the foods, and the tabulations of illness are presented. Fill in the attack rates where indicated. On the basis of your calculations, answer the following questions:
- What food or foods would you suspect caused the problem?
The foods that may have caused the problem include Rolls and Butter, Beef (rare), and Tuna Salad. These are the foods that had the highest percentage of ill student for those who ate at the cafeteria compared to those who did not eat.
- Based on the description of the clinical symptoms, what agent(s) do you think was (were) responsible? (Your best guess, no points will deducted for wrong answers to this question)
Based on the descriptions that were given on clinical symptoms, some of the infectious agents that may have resulted to the condition include Staphylococcus aureus or Staphylococcal food poisoning, which is associated with gastrointestinal syndrome and vomiting (Doménech, 2006). The other infectious agents that may have been involved are Campylobacter enteritis or Campylobacter jejuni, which are associated with diarrhea, malaise, abdominal pain, and fever (Chamberlain, 2013).
- Calculate the rate of illness in those who ate the food and those who did not eat the food.
The rate of illness was calculated using the formula below
Rate of illness=Number of those IllTotal number of those who ate the food
The calculated rates of illness for each of the food item served were as shown in Table 1 below.
- Calculate the rate differences. The rate difference is the rate of disease in the exposed or ill population minus the rate of disease in the unexposed or well population.
The rate of difference was calculated using the formula
Rate of difference=Rate of Disease in the exposed-rate of disease in the unexposed
The calculated rates of difference for each of the food item served were as shown in Table 1 below.
Staff then decided to perform a case control study to determine the risk associated with eating at the cafeteria. In addition to the 24 individuals who had eaten in the cafeteria and who presented ill in the college’s infirmary, staff identified an additional 6 individuals who were also seen in the infirmary with similar symptoms but who had not eaten in the cafeteria. Staff began interviewing additional students that were the same gender, and within ± 5 years of the age of the cases. Staff identified 76 individuals who were not sick and who also had eaten in the cafeteria on the day in question and 94 students who also were not ill and who had not eaten in the cafeteria on the day in question. What is the risk of becoming ill from eating in the cafeteria?
- Calculate the odds ratio, which is the risk of becoming ill from eating in the cafeteria
Odd Ratio=odds that an exposed person develops diseaseodds that a nonexposed person develops a disease
The calculated odd ratio is greater than 1 and, therefore, the risk of becoming ill after eating from the cafeteria is higher than the risk of not eating from the cafeteria. This shows that there is a positive association between eating in the cafeteria and becoming ill.
Chamberlain, N. (2013). Infections and Intoxications of the Intestines. Retrieved October 26, 2013, from http://www.atsu.edu/faculty/chamberlain/website/lectures/lecture/gi4.htm
Doménech, A. (2006). Gastrointestinal Tract Infections. Retrieved October 26, 2013, from http://www.uib.es/depart/dba/microbiologia/ADSenfcomI/material_archivos/infeccion%20gastrointestinal.pdf