Infectious disease outbreaks in Denmark Infectious Disease Epidemiology Course University of Copenhagen October 29, 2013 Luise Müller,
[email protected] Department of Infectious Disease Epidemiology, Statens Serum Institut
TODAY
What is an outbreak? Why investigate outbreaks? Who is doing what in the investigation of foodborne outbreaks in Denmark? Methodological steps in an outbreak investigation - Descriptive epidemiology - Analytical epidemiology Exercise: Playing the role of the epidemiologist…
WHAT IS AN OUTBREAK? Occurrence of more cases of a disease than expected - In a specific area - In a specific population - Within a specific time period
WHAT IS AN OUTBREAK? Occurrence of more cases of a disease than expected
- In a specific area - In a specific population - Within a specific time period Outbreak=epidemic Pandemic: an epidemic occurring worldwide, or over a very wide area, crossing international boundaries and usually affecting a large number of people*
*Last J. A dictionary of epidemiology (4th Edition) Oxford University Press 2001
WHY INVESTIGATE OUTBREAKS?
Stop the outbreak Understand what happened and why Prevent future outbreaks Improve our knowledge Improve surveillance and outbreak detection Training It is fun!
WHAT CAUSES FOODBORNE OUTBREAKS IN DENMARK?
2012
INVESTIGATION OF FOODBORNE OUTBREAKS IN DENMARK
Local outbreaks - E.g. restaurant, private party, drinking water
National outbreaks - Cases in two regions or more - International aspect
Responsible institutions - Regional food offices - Medical officer - Local laboratories
Responsible institutions - Statens Serum Institut • Reference laboratory • Department of infectious disease epidemiology - Veterinary and food administration - Food Institute at DTU
INVESTIGATION OF FOODBORNE OUTBREAKS IN DENMARK
Local outbreaks - E.g. restaurant, private party, drinking water
National outbreaks - Cases in two regions or more - International aspect
Responsible institutions - Regional food offices - Medical officer - Local laboratories
Responsible institutions - Statens Serum Institut • Reference laboratory • Department of infectious diseases - Veterinary and food administration - Food Institute at DTU
The Central Outbreak Management Group
TWO WAYS TO LOOK AT OUTBREAKS
The pathogen
Prove connection between human isolates and the source
The patients
Prove a statistical association between illness and exposure
STEPS IN AN OUTBREAK INVESTIGATION
1. 2. 3. 4. 5. 6.
7. 8. 9.
Confirm outbreak Confirm diagnosis Make a case definition Identify cases and obtain information Describe data: time, place, person Develop hypothesis Test hypothesis: Analytical studies Implement control measures Communicate results
NATIONAL OUTBREAK OF SALMONELLA STRATHCONA 2011
OUTBREAK SIGNAL SEPTEMBER 23, 2011
SSI laboratory reported 3 cases of Salmonella Strathcona First cases ever found in Denmark Literature search and international inquiry: no outbreaks ever reported No findings in food or animals BUT recent cases in Germany and Austria
STEPS IN AN OUTBREAK INVESTIGATION
1. 2. 3. 4. 5. 6.
7. 8. 9.
Confirm outbreak Confirm diagnosis Make a case definition Identify cases and obtain information Describe data: time, place, person Develop hypothesis Test hypothesis: Analytical studies Implement control measures Communicate results
CASE DEFINITION S. STRATHCONA OUTBREAK
A person with laboratory confirmed Salmonella Strathcona in Denmark from September-October 2011
- Who? - Where? - When?
STEPS IN AN OUTBREAK INVESTIGATION
1. 2. 3. 4. 5. 6.
7. 8. 9.
Confirm outbreak Confirm diagnosis Make a case definition Identify cases and obtain information Describe data: time, place, person Develop hypothesis Test hypothesis: Analytical studies Implement control measures Communicate results
STEPS IN AN OUTBREAK INVESTIGATION
1. 2. 3. 4. 5. 6.
7. 8. 9.
Confirm outbreak Confirm diagnosis Make a case definition Identify cases and obtain information Describe data: time, place, person Develop hypothesis Test hypothesis: Analytical studies Implement control measures Communicate results
EPICURVE Salmonella Strathcona, Oct 13, 2011 Denmark n=16, Germany n=10, Austria=1
Number of cases 5 4 3 2 1
8 28
7 4
JUNE
JULY
1* 8* 3* 26 27 28 29 30 31 1 2
4* 5 1 1* 3 4 5 6
AUGUST 2011 *Obs date of diagnosis
7
10 14 (1) (3) (3) 12 13 10 2 2 9 3 4 5 8 6 7 15 9 11 (9) 18 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1 2 SEPTEMBER 2011 DK: Lab Conf cases DK: Possible family cases DE: Lab conf cases DE: Family cases A: Lab conf cases
3
OCTOBER 2011
PLACE S. Strathcona, DK cases, October 13, 2011, n=24
PERSON
S. Strathcona Køn og alder n=27 (pr 13/9-2011) 7 6
Antal tilfælde
5 4
Mænd Kvinder
3 2 1 0 1-5
6-10
11-20
21-30
31-40
41-50
Aldersgrupper år
51-60
61-70
71-80
81-85
STEPS IN AN OUTBREAK INVESTIGATION
1. 2. 3. 4. 5. 6.
7. 8. 9.
Confirm outbreak Confirm diagnosis Make a case definition Identify cases and obtain information Describe data: time, place, person Develop hypothesis Test hypothesis: Analytical studies Implement control measures Communicate results
HYPOTHESIS-GENERATING INTERVIEWS 25 long interviews No travel No common events No specific food item Two supermarkets No connection to German/Austrian cases
Dead end…
COMPARATIVE ANALYSES OF PATIENTS’ SHOPPING LISTS
New way of thinking Information from 10 cases - supermarket address - date of shopping - credit card number Collaboration with supermarkets about getting data from their database Very time consuming!
COMPARATIVE ANALYSES OF PATIENTS’ SHOPPING LISTS
Comparison of patients shopping showed that 8/10 had bought the same small elongated tomatoes ”Datterino” By chance?
STEPS IN AN OUTBREAK INVESTIGATION
1. 2. 3. 4. 5. 6.
7. 8. 9.
Confirm outbreak Confirm diagnosis Make a case definition Identify cases and obtain information Describe data: time, place, person Develop hypothesis Test hypothesis: Analytical studies Implement control measures Communicate results
CASE CONTROL INVESTIGATION
25 cases and 56 population register controls Matched on age, gender, municipality
CASE CONTROL INVESTIGATION
Results - Supermarket A OR=16,9 [2,2-130] - Small elongated tomatoes OR=28, 95% CI [2,6-300]
TRACE BACK INVESTIGATION
Time of sale in Supermarket A corresponded to the date of onset for cases Traced back to Italian producer Tomatoes also sold in Germany and Austria Test of tomatoes -> negative - Germany later batches - Italy at the producer
STEPS IN AN OUTBREAK INVESTIGATION
1. 2. 3. 4. 5. 6.
7. 8. 9.
Confirm outbreak Confirm diagnosis Make a case definition Identify cases and obtain information Describe data: time, place, person Develop hypothesis Test hypothesis: Analytical studies Implement control measures Communicate results
CONTROL MEASURES
Tomatoes no longer in the supermarket! Communication
COMMUNICATION Outbreak report International communication SSI.dk Scientific article
LESSONS LEARNED IN THIS OUTBREAK Why investigate outbreaks? Stop the outbreak Understand what happened and why Prevent future outbreaks Improve our knowledge Improve surveillance and outbreak detection Training It is fun!
Not possible Tomatoes a new source in DK Communication New salmonella serotype Credit card investigation Our EPIET students took part in the investigation It was a lot of hard work –but definitely fun
S. STRATHCONA CASES SEP-OCT 2011, N=40 43 Denmark (epicurve) 5 Germany 2 Italy 1 Austria
Number of cases 5 4 3 2 1
33
1 3 4 5
6
7
8
29 12 22 2 3 4 5 8 6 7 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
SEPTEMBER 2011
14 24 13 10 30 15 9 11 16 20 24 25 26 27 28 29
41 25 17 30
38 35 18 1 2
19 31 26 34 37 21 32 27 3 4 5 6
28 7 8
39 36 42 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 OCTOBER 2011
S. STRATHCONA CASES SEP-OCT 2011, N=42
S. STRATHCONA CASES AGE AND SEX 2011, N=43
CHALLENGES IN OUTBREAK INVESTIGATION Work against time Political/media pressure Don´t have full information when you start (react on small signals) Interviews can be difficult - Food history hard to remember - Selective memory - Very ill/dead people In-depth epidemiological analyses often not possible (quick and dirty) Difficult to find pathogen in the food Hidden ingredients Unequal distribution in the food and difference in susceptibility Multiple sources We don’t always find the source
TAKE HOME MESSAGE Outbreak investigation is an important part of the prevention of infectious diseases Outbreak investigation demands a close cooperation between different institutions Interviews and statistical tools are important components of epidemiological methods It is fun, informative and never predictable
IF YOU WANT TO KNOW MORE… Control of Communicable Diseases Manual. Heyman 2008 Annual report on Zoonoses in Denmark 2012
Vejledning i opklaring af fødevare- og vandbårne udbrud (under revision) Statens Serum Institut www.ssi.dk - Epi-Nyt/Epi-News (weekly bulletin) - Sygdomsleksikon - Overvågning i tal og grafer - Opklaring af fødevarebårne udbrud i DK European Centre for Disease Prevention and Control www.ecdc.europe.eu
- Communicable disease threats report (weekly) - EPIET training - Eurosurvelliance (Rapid communications) World Health Organization www.who.int - Disease outbreak news
SELECTED OUTBREAKS 2011
Botulisme i tofu
Norovirusudbrud Køge sygehus
Salmonella Typhimurium i røget mørbrad
Januar
Februar
Marts
Leptospirose efter skybrud i København
VTECO104 Tyskland
April
Maj
Juni
Juli
August
September
Salmonella Strathcona i tomater
Oktober
November December
