1. Our vision: Healthier communities, Excellence in healthcare Our values: Teamwork, Honesty, Respect, Ethical, Excellence, Caring, Commitment, Courage Descriptive data collection and analysis Prepared by Dr Craig DaltonPublic Health Physician Hunter New England Population Health Advanced Foodborne Disease Outbreak Workshop Viet Nam

2. 2 The steps of descriptive epidemiology include: WHO Outbreak Guidelines:  establishing a case definition;  identifying cases and obtaining information from them;  analysing the data by time, place and person characteristics;  determining who is at risk of becoming ill;  developing hypotheses about the exposure/vehicle that caused the disease;  comparing the hypotheses with the established facts;  deciding whether analytical studies are needed to test the hypotheses.

3. 3 Outline  Descriptive data collection and analysis well covered so far  Focus on some learning points  Some examples from my “epi scrap book”

4. 4 Case definition for Irish BBQ outbreak TimePlacePerson SuspectOnset after July 18th in people who attended the fundraiser BBQ who had diarrhoea and/or vomiting. Probable as above as above + had Salmonella isolated from stool. Confirmed as above as above + had Salmonella Enteritidis isolated from stool.

5. 5 Most sensitive but could be any cause of diarrhoea – less specific Most specific, but may miss many cases that are not tested – less sensitive

6. 6 Epi Curve  Histogram  Distribution of cases by time of onset of symptoms, diagnosis or identification –time interval depends on incubation period1/4 - 1/6 Cases Days

7. 7 Epi curve  Describe –start, end, duration –peak –importance –atypical cases  Helps to develop hypotheses –incubation period –etiological agent –type of source –type of transmission –time of exposure Cases Days

8. 8 Epicurves hours cases Week weeks Common point sourceCommon persistent source Propagated source

9. 9 Onset of illness among cases of E. coli O157:H7 Infection, Massachusetts, December, 1998. Calculating Incubation Period

10. 10 William Keenes Foodborne Resourcess http://www.oregon.gov/DHS/ph/acd/keene.shtml Shotgun, or trawling, Or trolling questionnaire 100+ foods

11. 11 May need modification for Viet Nam?

12. 12 Collecting risk factor information  From page 19 WHO Manual.. “In protracted outbreaks, when investigating illnesses with incubation periods longer than 72 hours (e.g. hepatitis A, typhoid fever, listeriosis) or when a person does not remember specific foods eaten, questions should be asked about food preferences, i.e. foods usually eaten or routine dietary habits.”

13. 13 Food preference  We missed the slow increase of an unusual strain - Salmonella Mbandaka – laboratory serotyping was months behind.  Began the case interviews 3 months after the start of the outbreak.  In mid June we asked cases about illness back to mid March.  Would they remember??

14. 14 So we asked….  In a typical week in the months of April through May, would you say you ate the following food: –Always (ate daily) –Sometimes (at least once per week) –Never (do not eat this food)  For 105 foods - we asked very specific questions about brands of food, where they purchased it from, and how they cooked the food.  By asking about “typical” food preferences it was easy to ask many questions without “stressing” the cases, did not force them to try to remember 2 month food history exactly

15. 15

16. 16 Epidemiology and Infection 2000 V124 p418 Airborne transmission of norovirus

17. 17 Cases by delivery time

18. 18 E. coli O157:H7 Cases by Age and Gender CDC Case Study Alfalfa Sprouts and other “fancy” salads in 20 to 60 yo females.

19. 19 Take home messages..  Play with your data  Don’t rush to analytical epidemiology  Read outbreak investigations in good journals to inspire your creativity and get ideas for interesting descriptive analysis  Keep a “scrapbook” of great examples

20. 20 Thank you  With grateful acknowledgements of all the foodborne disease epidemiologists in OzFoodnet and Hunter New England Population Health Hunter New England Population Health is a unit of the Hunter New England Area Health Service. Supported by funding from NSW Health through the Hunter Medical Research Institute. Developed in partnership with the University of Newcastle.