Questions and Topics We Can Help You To Answer:
Paper Instructions:

CASE STUDY QUESTIONS    

Question 1A: What could account for the increase in cases reported to MDCH? 

Question 1B: What information might help determine which of these explanations is the most likely cause of the increased numbers? 

Question 2: Compare the DNA fingerprints in Figure 2 from seven of the Michigan E. coli O157:H7 cases. Each isolate has its own vertical lane (i.e., column). Controls appear in lanes #1, 5, and 10. 
Which Michigan isolates appear similar? 

Question 3: What are the advantages and disadvantages of this case definition? How might you change it? 

Question 4: Compare the age and gender distribution of E. coli O157:H7 cases from the Michigan outbreak and those reported from U.S. FoodNet sites in 1997. (see Appendix 1) 

Question 5: What kinds of questions would you ask in the hypothesis-generating interviews? Be sure to consider all possible modes of transmission of E. coli O157:H7. 


Question 7: Given your knowledge about E. coli O157:H7, the descriptive epidemiology of the initial cases, and the results of hypothesis-generating interviews, outline the information available at this point on the source of the outbreak and mode of transmission and state your leading hypothesis. 
Question 8A: How would you define controls for this study? 

Question 8B: Do you agree with the investigators’ decision to match on age group and gender? Why or why not? 

Question 9: What methods might be used to identify controls? What are the advantages and disadvantages of each method? 

Question 10: Over what time period would you examine exposures to possible risk factors for cases? For controls? 

Question 11: What are possible explanations for the association between illness and sprouts? 

Question 12: How might you explain the 12 ill persons in the study who did not report eating alfalfa sprouts in the 7 days before they became ill? 

Question 13: What control measures might you consider at this point? What further studies might you suggest? (See Appendix 3 for a description of alfalfa sprouts and the typical sprouting procedure.) 

Question 14: What criteria should be considered before deciding to undertake a traceback procedure? Would you consider doing a trace back in the Michigan outbreak? 

Question 15: What information on the implicated food item might facilitate the traceback process? 

Question 16: Given the results of the Michigan and Virginia traceback investigations, where is the most likely point of contamination in the production of the sprouts? 

Question 17: In inspecting the alfalfa fields and harvesting process, what possible points of contamination should you consider? 

Question 18: What interventions/control measures would you suggest at this point? 

Question 19: What type of intervention is likely to be most effective against the problem of sprout contamination: education of producers, education of consumers, or changes in methods of product processing? Why? 




Question GUIDE (What I am looking for in each question)

PLEASE USE THIS GUIDE WHILE ANSWERING QUESTIONS.

1A) You may want to characterize reasons for the increase as artificial (e.g. increase in culturing, new testing procedures, data entry errors, lab errors, etc) versus real (e.g. changes in population and/or infection rate).

1B) Discuss procedures with lab and surveillance staff to identify potential issues.

2) Look for similar banding patterns. Those with up to one band difference are similar.

3) A case definition is a standard set of criteria used to determine whether individuals are classified as having the disease in question (cases) or not (controls). This includes clinical criteria (signs, symptoms, lab results) and time, place, and person.

4) A graph may facilitate comparisons.

5) This is done to identify all potential sources of infection. Commonalities among cases will ultimately provide a hypothesis on the source of the outbreak. Questions should include: demographics, date of onset, duration, severity, hospital/doctor visits, 7 day food and water history, exposure to other ill adults, children, farm animals, travel.

6) You may skip question #6.

7) Summarize what you have learned thus far.

8A) Controls are individuals without the disease in question but are representative of the community. Controls should be at risk, have potential for exposure but be independent of their exposure status.

8B) Matching refers to selecting controls with characteristics similar to cases such as age, sex, and geographic area. This minimizes the risk of confounding.

9) Possible methods include random digit dialing, neighborhoods, referrals from patients, and referrals from physicians. Choose one of these and list some advantages and disadvantages of your decision.

10) Traditionally, information on cases is selected approximately one week prior to the onset of disease. Controls are generally matched to cases.

11) Chance, selection bias (persons with exposure more likely to be cultured), information bias (cases more likely to accurately remember diet than controls), confounding (sprouts may have been associated with some other food that is the true cause), true association.

12) May have forgotten, cross-contamination, longer incubation period, controls infected by cases, some other cause.

13) Decide whether you have enough information to implicate a specific source. If not, suggest further studies such as culturing suspected source, traceback along chain of production, further examine cases not associated with suspected source for other possible routes of infection.

14) Evidence, environmental and/or production contamination, scope of outbreak, precedence for this type of infection, microbiological evidence. Justify your decision.

15) All steps between harvest and consumption should be considered. Product ID, lot #’s, sell-by & expiration dates, manufactures, wholesalers, distributors, shipping procedures.

16) Use the information you have gathered to establish a hypothesis. 17) If contamination occurred what are potential sites?

18) Consider short and long-term measures.

19) Changes in product processing