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Outbreak investigations Biagio Pedalino & Domenico Martinelli 24 th October 2012.

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Presentation on theme: "Outbreak investigations Biagio Pedalino & Domenico Martinelli 24 th October 2012."— Presentation transcript:

1 Outbreak investigations Biagio Pedalino & Domenico Martinelli 24 th October 2012

2 Objectives for this session Describe –the principles of outbreak investigation –the steps in outbreak investigation Using practical example –Foodborne outbreak during a birthday party in a pub

3 What do you normally do on Sunday afternooon?

4 Roberto, 41 Pub owner Something funny. We had lunch at sibillas. We were 13 and now 7 are vomiting… Excellent. Do you need me to be there for the plasil? Have you eaten something with cream?

5 What is it? Friendly call Need of medical assistance? Coincidence? What else?... Outbreak?

6

7 What is an outbreak ? The occurrence in a community or region of cases of an illness (or an outbreak) with a frequency clearly in excess of normal expectancy [Heymann DL, CDC Manual – 19 th Ed]

8 Outbreak investigation: tasks Confirm outbreak and diagnosis Form Outbreak Control Team Define a case (case definition) Identify cases and obtain information Describe data by time, place, person Develop hypothesis Test hypothesis: analytical studies Additional studies Communicate results: –outbreak report, publication Implement control measures Control measures Communication

9 Confirm outbreak Is this an outbreak? More cases than expected? Surveillance data Surveys: hospitals, labs, physicians Caution! Seasonal variations Notification artefacts Diagnostic bias (new technique) Diagnostic errors (pseudo-outbreaks)

10 Confirm diagnosis Laboratory confirmation –serology –isolates, typing of isolates –toxic agents Meet attending physicians Examine some cases Contact (visit) the laboratories Not always necessary to confirm all the cases but confirm a proportion throughout the outbreak

11 Outbreak confirmed Immediate control measures? - prophylaxis - exclusion / isolation - public warning - hygienic measures - others

12 Alert !!! Informal alert from the pub – 16:43: Alert 7 participants were sick with vomit Formal intervention: a simple phone call !

13 Phone call 4:45 pm Talk to the pub owner –How many people (list with contact details) –Food items –Symptoms/treatment Impose preventive closure of the pub

14 Outbreak confirmed Immediate control measures? Further investigation? - prophylaxis - exclusion / isolation - public warning - hygienic measures - others - etiological agent - mode of transmission - vehicle of transmission - source of contamination - population at risk - exposure causing illness

15 Steps of an outbreak investigation Confirm outbreak and diagnosis Form Outbreak Control Team Define a case Identify cases and obtain information Describe data by time, place, person Develop hypothesis Test hypothesis: analytical studies Additional studies Communicate results: –outbreak report, publication Implement control measures Control measures

16 My outbreak control team Ale, Preventive medicine school student - II yr Fra, PHD student - I yr

17 Case definition A person presenting with vomit or nausea or diarrhoea, within 24 hours after participating at the meal in the pub (Sunday January 22nd; 2pm)

18 Case definition Standard set of criteria for deciding if a person should be classified as suffering from the disease under investigation Criteria –clinical and/or biological criteria –time –place –person

19 Case definition Simple, practical, objective Sensitive? Specific? Multiple case definitions –confirmed –probable –possible CD can be adjusted, if new information becomes available

20 Steps of an outbreak investigation Confirm outbreak and diagnosis Form Outbreak Control Team Define a case Identify cases and obtain information Describe data by time, place, person Develop hypothesis Test hypothesis: analytical studies Additional studies Communicate results: –outbreak report, publication Implement control measures Control measures

21 Descriptive epidemiology - When did they become ill? (time) - Where do they live? (place) - Who are the cases? (person)

22 Identify & count cases Obtain information Identifying information Demographic information Clinical details Exposures and known risk factors notifications hospitals, GPs laboratories schools workplace, etc

23 Monday 8 am Contact the participants: –Symptoms –Food consumption –Stool specimen collection (n=5) In the pub Food samples collection Info on food preparation

24 Information collected: symptoms 14:00: lunch (13 participants: birthday party) –12 were sick Vomit (n= 10) Nausea (n=9) Diarrohea (n=5) Abdominal pain (n=6) Fever (<38°C; n=2)

25 Information collected: food consumption (n=13) Basmati rice: 92% (12) Ragu : 77% (10) Red rice: 69% (9) Apple cake: 61% (8)

26 Possible cause of the outbreak? Virus ? Bacteria ? Toxins ? Parasite ?

27

28 Organize information: Line list Names Date of birth Addresse Onset of symptoms Treating physician Hospital stay Laboratory results

29 Line List Case No. Name Date of birth Addresse Date of onset Lab results 123456123456 XY AB CD …

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31 Identify & count cases Obtain information Descriptive study Describe in - time - place - person

32 Time: Epidemic Curve Histogram Distribution of cases by time of onset of symptoms, diagnosis or identification –time interval depends on incubation period Cases Days

33 Epidemic 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

34 Examples of Epidemic curves hours cases days weeks Common point source Common persistent source Propagated source cases days Common intermittent source

35 Hepatitis A by date of onset Ogemaw county, Michigan, April - May 1968 281420262814202617 Days 0 5 10 15 Number of cases one case 30 days 15 days 50 days Exposure

36 Hypothesis on the moment of infection unknown pathogen and point source 0 5 15 1357911131517192123252729 Time 1 median 50% 50% 3 Possible moment of infection 2 ~ median incubation period (= duration of the epidemic)

37 Epi curve Incubation period: Median = 2 hrs Range = 1-5 hrs Incubation period: Median = 2 hrs Range = 1-5 hrs

38 Place Place of residence Place of possible exposure –work –meals –travel routes, –day-care –leisure activities Maps –identify an area at risk

39

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41 Person Distribution of cases –age –sex –occupation, etc Distribution of these variables in population Attack rates

42 Roberto 41 yrs old Roberto 41 yrs old Yasemin 35 yrs old Yasemin 35 yrs old Marygiò 42 yrs old Marygiò 42 yrs old Massimo 40 yrs old Massimo 40 yrs old Barbara 34 yrs old Barbara 34 yrs old The grandmother, 70 yrs old

43 Steps of an outbreak investigation Confirm outbreak and diagnosis Form Outbreak Control Team Define a case Identify cases and obtain information Describe data by time, place, person Develop hypothesis Test hypothesis: analytical studies Additional studies Communicate results: –outbreak report, publication Implement control measures Control measures

44 Develop hypotheses - Who is at risk of becoming ill? - What is the disease? - What is the source and the vehicle? - What is the mode of transmission?

45 Hyp in the pub: summary Close community 12 out of 13 were sick Mainly vomit Basmati rice mostly consumed food Basmati rice left out of the fridge for > 24hrs

46 Compare hypotheses with facts Test specific hypotheses Analytical studies - cohort studies - case-control studies

47 Testing hypothesis Cohort -attack rate exposed group -attack rate unexposed group Case control -proportion of cases exposed -proportion of controls exposed

48 Cohort study Among participants Telephone interviews

49 Description of the cohort 13 persons –54% F –Median age: 42 (15 – 70) Overall Attack Rate (AR): 92% Food specific AR: –Basmati rice: 100% –Apple cake: 100% –Ragu: 91% –Red rice: 90%

50 Steps of an outbreak investigation Confirm outbreak and diagnosis Form Outbreak Control Team Define a case Identify cases and obtain information Describe data by time, place, person Develop hypothesis Test hypothesis: analytical studies Additional studies Communicate results: –outbreak report, publication Implement control measures Control measures

51 Verify hypothesis Additional investigations Microbiological investigation of food samples Environmental investigation Veterinarian investigation Molecular Typing Trace back investigations (origin of foods) Meteorological data Entomological investigations

52 Tuesday 10 am: laboratory results

53 2/5 faecal specimens

54 Steps of an outbreak investigation Confirm outbreak and diagnosis Form Outbreak Control Team Define a case Identify cases and obtain information Describe data by time, place, person Develop hypothesis Test hypothesis: analytical studies Additional studies Communicate results: –outbreak report, publication Implement control measures Control measures

55 Outbreak report Regular updates during the investigation Detailed report at the end –communicate public health messages –influence public health policy –evaluate performance –training tool –legal proceedings

56 Actions & Recommendations Pub closed for one day Appropriate food preparation (cold chain, storage, etc) Timely alert for prompt intervention … To follow grandmothers wisedom… « no thanks, no rice for me… »

57 The reality…. Outbreak suspected time Confirmation Form Outbreak Control Team Confirm Diagnosis Site visit Case definition Line list Organize Data Descripitve Epidemiology Control measures Analytical Epidemiology Recommendations Report Publication Communication

58 Why investigate outbreaks? Stop the outbreak Understand what happened and why Prevent future outbreaks Improve our knowledge Improve surveillance and outbreak detection Training

59 Acknowledgements Pub owner Participants of the party (special thanks to the grandmother)

60 Questions ???


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