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 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 Outline Descriptive data collection and analysis well covered so far Focus on some learning points Some examples from my “epi scrap book”
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 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 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 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 Epicurves hours cases Week weeks Common point sourceCommon persistent source Propagated source
9 Onset of illness among cases of E. coli O157:H7 Infection, Massachusetts, December, Calculating Incubation Period
10 William Keenes Foodborne Resourcess Shotgun, or trawling, Or trolling questionnaire 100+ foods
11 May need modification for Viet Nam?
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 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 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
16 Epidemiology and Infection 2000 V124 p418 Airborne transmission of norovirus
17 Cases by delivery time
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 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 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.