ExercisesSlidesv2

Fundamentals of Epidemiology andOutbreak Investigations:Group Exercises : 

Fundamentals of Epidemiology and Outbreak Investigations: Group Exercises Version 2 February 2006

Exercise 1: 

Exercise 1

Scenario 1: 

Scenario 1 Your local health department has received a series of reports of illness from the recent Cleveland-McKay wedding. Your health department has collected information on five suspected cases. Your director of health hands you the case report forms and asks you to draw up a line listing.

Creating a Line Listing: 

Creating a Line Listing The choice of information to include in a line listing is somewhat arbitrary. The following is a list of commonly included categories of information Identifying information Descriptive information (person, time, place) Clinical information Risk factor information

Example of a Line Listing: 

Example of a Line Listing

Exercise 1: 

Exercise 1 Create a line listing for the Cleveland-McKay outbreak

One Possible Answer: 

One Possible Answer Here is one way that a line listing might be drawn up from the five case report forms on the Cleveland- McKay wedding outbreak:  

Exercise 2: 

Exercise 2

Scenario 2: 

Scenario 2 The manager of a grocery store has reported to your health department a rash illness among the store’s workers. The director of health has assigned a team to go to the store and investigate. The team has conducted interviews of the workers.

Grocery Store Rash Table : 

Grocery Store Rash Table

Exercise Two: 

Exercise Two What type of epidemiological study should be used to determine the source of the outbreak? Why? What is the appropriate measure of association? After reviewing the table showing the data on exposure to celery for these workers Calculate the measure of association Interpret the results for your director of health.

Exercise 2: Answers: 

Exercise 2: Answers Question 1 - You would use a cohort study because the outbreak is small and confined. Question 2 - The appropriate measure of association for a cohort study is relative risk.

Measures of Association: 

Measures of Association Attack Rate - exposed group: Number of people who ate item and became ill / Total number of people who ate that item. Attack Rate - not exposed group: Number of people who did not eat item and became ill / Total number of people who did not eat that item. Relative risk: Attack rate in exposed group / Attack rate in the not exposed group

Grocery Store Rash Table – with attack rates and relative risk: 

Grocery Store Rash Table – with attack rates and relative risk

Exercise 2: Answers: 

Exercise 2: Answers Question 3a The attack rate for exposed workers = 25 / 56, or 44.6%. Attack rate for workers who were not exposed = 5 / 70, or 7.1%. Thus, the relative risk for exposure to celery = 44.6 / 7.1, or 6.3.

Exercise 2: Answers: 

Exercise 2: Answers Question 3b Workers who were exposed to celery were 6.3 times more likely to develop the rash illness than those who were not Therefore the celery may have been the source of the outbreak.

Exercise 2: Answers: 

Exercise 2: Answers Question 3b continued To examine the role of chance, you should calculate a test of statistical significance (i.e. chi-square) and look up the corresponding p-value in a table. If the p-value is below 0.05, your findings would be considered statistically significant