Outbreak investigation 2008

Outbreak Investigation Dr.Kedar Karki What is an outbreak ? Occurrence of more cases of disease than expected – in a given area – over a particular period of time – among a specific group of people Why investigate outbreaks? • • • • • • Stop the outbreak Understand what happened and why Prevent future outbreaks Improve our knowledge Improve surveillance and outbreak detection Training Objectives for this session • Describe – the principles of outbreak investigation – the steps in outbreak investigation • Using practical examples – Outbreak of Hepatitis A in Ibiza, Spain September 2000 - January 2001 • Tomorrow – some operational and logistical aspects of outbreak investigation Investigation Surveillance Dead Sick Prediction Exposed Epidemiology Vector Reservoir Clinicians Co-ordination Food safety Supply channels Trace back Laboratory Clinical Investigation Specimen transfer Diagnostic Media Authorities Decisions Infrastructure Regulations Vaccinations etc Specific demands when investigating outbreaks • Unexpected event • Act quickly • Rapid control • Interdisciplinary coordination • Work carried out in the field Systematic approach Outbreak of Hepatitis A in Ibiza (Spain) 2000/2001 • Ibiza is a major tourist destination (2 million visitors in 2000) • 23-27 October 2000: 5 cases of Hepatitis A notified to local health authorities in Ibiza • 3 cases of Hepatitis A among German tourists returning from Ibiza 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 Detection Routine surveillance Clinical / Laboratory General public Media Notified cases of S. Bovismorbificans, Germany 2002-2005 no. cases 120 100 80 60 40 20 0 2002 (n=184) 2003 (n=150) 2004 (n=153) 2005 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) Outbreak of Hepatitis A in Ibiza, Spain • Hepatitis A notifiable disease in Spain • notifications in Ibiza during previous years: – 1997: 6 cases – 1998: 0 cases – 1999: 4 cases 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 Outbreak confirmed  Immediate control measures? - prophylaxis - exclusion / isolation - public warning - hygienic measures - others Further investigation? - aetiological agent - mode of transmission - vehicle of transmission - source of contamination - population at risk - exposure causing illness Outbreak confirmed, further investigations warranted Form Outbreak Control Team Epidemiologist Microbiologist Clinician Environmentalist Engineers Veterinarians Others Team coordinates field investigation Descriptive epidemiology - Who are the cases? (person) - Where do they live? (place) - When did they become ill? (time) 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 Case definition • Simple, practical, objective • Sensitive? • Specific? • Multiple case definitions – confirmed – probable – possible Case definition Outbreak of Hepatitis A in Ibiza 2000/2001 Any person • with IgM antibodies to Hepatitis A Virus August 2000 - January 2001 • on the island of Ibiza for at least one day during a 15-50 day period before onset of illness or seroconversion Identify & count cases notifications hospitals, GPs laboratories schools workplace, etc Case-finding Outbreak of Hepatitis A in Ibiza 2000/2001 • Contacting clinicians and laboratories on the island • Note in German Epidemiological Bulletin • Enquiries through European network Identify & count cases Obtain information Identifying information Demographic information Clinical details Exposures and known risk factors Obtaining information Outbreak of Hepatitis A in Ibiza 2000/2001 • Trawling questionnaire • Place and time of stay on Ibiza • Food histories: – What eaten – Where bought? – Visit to restaurants Organize information: Line list • • • • • • • Names Date of birth Addresse Onset of symptoms Treating physician Hospital stay Laboratory results Line List Case No. Name XY AB CD … … … Date Addresse of birth Date of onset Lab results 1 2 3 4 5 6 Identify & count cases Obtain information Describe in - time - place - person Analysis of descriptive data Time: Epi Curve • Histogram • Distribution of cases by time of onset of symptoms, diagnosis or identification – time interval depends on incubation period Cases 10 9 8 7 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 10 11 12 Days Epi curve • Describe – start, end, duration – peak – importance Cases 10 9 8 7 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 10 11 12 – atypical cases – – – – – incubation period etiological agent type of source type of transmission time of exposure • Helps to develop hypotheses Days Examples of Epicurves Common point source cases 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 cases 10 9 8 7 6 5 4 3 2 1 0 1 2 Common persistent source 3 4 5 6 7 8 9 10 11 12 hours cases 12 10 8 6 4 2 0 1 2 3 4 5 6 7 8 9 10 11 12 13 days cases 10 9 8 7 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Propagated source Common intermittent source weeks days Cases of Hepatitis A in Ibiza by week of onset, 2000/2001 cases 10 9 8 7 6 5 4 3 2 1 0 tourists residents 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 1 week number August September October November December January Estimation of time or period of exposure cases 6 5 4 3 2 1 0 1 2 3 max incubation min 4 5 6 7 8 exposure Outbreak of typhoid fever, Germany 2004 Longest incubation period: 60 days suspected case probable case confirmed case N° cases Shortest incubation period: 5 6 15 April 25 May 26 27 28 29 30 31 1 J une 2 3 4 5 6 7 8 9 10 11 3 12 2 1 13 4 14 15 Probable time period of infection Place • Place of residence • Place of possible exposure – work – meals – travel routes, – day-care – leisure activities • Maps – identify an area at risk Cases of Hepatitis A in Ibiza by place of residence, 2000/2001 Portinatx Ibiza-City 10 km Person • Distribution of cases – age – sex – occupation, etc • Distribution of these variables in population • Attack rates Outbreak of S. Agona, Germany 2003 2002 - S. Agona notifications 2002 2003 - Meldungen S. Agona 2003 30 25 20 30 25 20 15 10 5 0 No. cases 15 10 5 0 No. Cases 10-14 15-19 20-24 25-29 30-39 40-49 50-59 10-14 15-19 20-24 25-29 30-39 40-49 50-59 60-69 age (years) age (years) 60-69 70+ 70+ 1 2 3 <1 4 5-9 5-9 1 2 3 <1 4 Cases of Hepatitis A in Ibiza by age group, 2000/2001 percentage 25 20 15 10 5 0 0-4 5-9 10-14 15-19 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 age (years) 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? exploratory interviews among cases of Hepatitis A, Ibiza 2000/01 • 3 potential risk factors: – visited a restaurant in the harbour of Ibiza town – bought food at a supermarket in the centre of the town – stayed at Hotel in Portinatx (German tourists) Compare hypotheses with facts Test specific hypotheses Analytical studies - cohort studies - case-control studies Testing hypothesis • Cohort - attack rate exposed group - attack rate unexposed group • Case control - proportion of cases exposed - proportion of controls exposed Case-control study Outbreak of Hepatitis A in Ibiza 2000/2001 • among residents of the island • one control per case • selected from the data-base of the health registration card • matching for age and neighbourhood • no history of hepatitis A disease or vaccination. Cases of Hepatitis A and controls by exposure to restaurant and shop, Ibiza 2000/2001 Exposure Cases (n=38) 22 (57.9%) 13 (34.2%) Controls (n=38) 5 (13.2%) 6 (15.8%) matched OR 9.0 4.5 95% CI Restaurant Shop 2.1-38.8 0.97-20.8 Cases of Hepatitis A and controls by exposure to food items, Ibiza 2000/2001 Restaurant Salad Cases n = 22 18 Controls n=5 0 Matched OR undef. 95% CI Shop Sausages Meat Vegetables Fish Bread n = 13 11 10 11 9 8 n=6 3 4 4 4 4 5.5 1.67 1.67 1.13 0.8 0.4-87.3 0.1-21.1 0.1-21.1 0.1-12.6 0.1-8.6 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 Viral genome sequencing Outbreak of Hepatitis A in Ibiza 2000/2001 • Alignment of aminoterminal region of VP3 • 38 serum samples • Positive in 11 cases: – belonging to the three different groups – 100% homology Food trace-back NL Schleswig-Holstein Mecklenburg-Vorpommern Hamburg Bremen Niedersachsen Berlin Brandenburg Sachsen-Anhalt Nordrhein-Westfalen Sachsen Thüringen Hessen Outbreak of S. Bovismorbificans, Germany 2004 Rheinland-Pfalz Saarland Bayern Baden-Württemberg Implement control measures May (must) occur at any time during the outbreak!! At first, general measures According to findings, more specific measures 1) Control the source of pathogen 2) Interrupt transmission 3) Modify host response Recommendations Outbreak of Hepatitis A in Ibiza 2000/2001 • Emphasise hygiene amongst food handlers • Strengthen surveillance for foodborne diseases • Enhance international co-operation 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 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 The reality…. time Confirmation Site visit Recommendations Report Publication Case definition Organize Data Confirm Diagnosis Info: Outbreak suspected Form Outbreak Control Team Descripitve Epidemiology Line list Analytic Epidemiology Control measures