Principles of Outbreak invEstigation

1. Principles of Outbreak invEstigation KaroonChanachai Bureau of Disease Control and Veterinary Service Department of Livestock Development, Thailand

2. An event (1) • On 28 May 2009, you were still at your work, when an email from your counterpart at the National Institute of Animal Health (NIAH) popped up. In an attachment, you found an official laboratory report from the Upper Northern Regional Veterinary Research and Diagnostic Center. It was a laboratory confirmed case of classical swine fever (CSF) in Mae Salong, Chiangrai province

3. An event (2) • Early September 2007, Khon Kean Provincial livestock office notified to Department of Livestock Development (DLD) that there was suspected porcine disease occurred in pig farms in Silasubdistrict, Muang district. Symptoms of infected pigs were fever, cough, blue ears, and petechial hemorrhage.

4. Do we think this is an outbreak?, why? Will we do anything after receiving this report ?

5. Definition of outbreak • Occurrence of more cases of disease than expected in a given area among a specific group of people over a particular period of time or • Two or more linked cases of the same illness or • New diseases What is the level of expected ?

6. Excess of Expected Level More than • Median number of cases in previous 5 years or • Average number of cases + 2sd of previous 5 yr

7. Judged to be an outbreak A single case of disease that has never been occurred before. 1997: A 3-year old boy, case of Avian Flu (H5N1) in Hong Kong alerted the public health people around the world to start a full scale investigation.

8. Who? When? Where? What? Descriptive epidemiology Why? Analytical epidemiology How to react? Epidemiology for action

9. Specific demands when investigating outbreaks • Unexpected event • Need to act quickly • Need for rapid control • Work carried out in the field Systematic approach

10. Unexpected event !!!

11. Steps of an outbreak investigation • Prepare for field work • Establish the existence of an outbreak • Verify the diagnosis • Construct a working case definition • Find case systematically and record information • Perform descriptive epidemiology • Develop hypothesis • Analytical studies to test hypotheses • Special studies (e.g. environmental study) • Implementation of control measures • Communication, including outbreak report

12. Diagnosis verified ? clinical + laboratory Link between cases? Expected numbers? Routine surveillance Clinical / Laboratory General public Media Detection Is this an outbreak?

13. Sequence of events in outbreak detection and confirmation (I) 1st cases notified by Local officer Primary Case Report Samples taken Lab result Response begins CASES Opportunity for control DAY

14. Sequence of events in outbreak detection and confirmation (II) Response begins Prim Noti Rep Samp Lab Potential cases prevented CASES DAY

15. Outbreak confirmed Immediate control measures? Further investigation?

16. Assistance ? Outbreak confirmed Immediate control measures? Further investigation? Unknown aetiology (pathogen/source/transmission) Cases serious Cases still occurring Public pressure Training opportunity Scientific interest Prophylaxis Quarantine / isolation Public warning Hygienic measures Surveillance

17. Epidemiologist Microbiologist Environmental specialist Ministry / Government Press officer Others FIELD Outbreak Investigation Team?

18. 

19. Preparing for field works • Team members and roles • Necessary Knowledge and equipments; specimen collection & transport method, etc. • Lines of communication

20. An event (2) • Early September 2007, Khon Kean Provincial livestock office notified to Department of Livestock Development (DLD) that there was suspected porcine disease occurred in pig farms in Silasubdistrict, Muang district. Symptoms of infected pigs were fever, cough, blue ears, and petechial hemorrhage.

21. Review of Pig Diseases • There are many disease that cause a lot of death with fever, cough, blue ears, and skin petechial hemorrhage in pig. • The diseases can cause by PRRS, Swine fever, African swine fever, Mycoplasma and other bacterial infection. • ………………. • ……………… • ………………

22. Descriptive epidemiology Epidemiologist Microbiologist, Pathologist Environmental specialist Ministry / Government Press officer Others Outbreak Investigation Team? Assess situation Examine available information Preliminary hypothesis ? Case definition Case finding

23. Reported cases (Passive cases) • Cases in community (active cases) • Mild or no symptom • Treated by owner • Self recovering • Death • These cases can be potential spreader (Active cases)

24. Case definition • Standard set of criteria for deciding if an individual animal/flock should be classified as suffering from the disease under investigation. • Clinical criteria, restrictions of time, place, person • Unit of interest • Simple, practical, objective • Sensitivity

25. Case definition: • Suspect farm was defined as pig farm in village Moo.13 and surrounding villages, Salasubdistrict, Khon Kean province that have • more than 30% of pigs having cough, petechial hemorrhage or reproductive or respiratory tract problems or • mortality rate more than 10% • during the period 1 August – 30 November 2007

26. Case definition: categorisation • Suspect • Farm that met suspect case definition • Confirmed • The confirmed farm was defined having at least one of pig positive to ………

27. Methodology: Case finding • Active case finding was conducted by doing a census among all pig farms in the village 13 and nearby villages. • Interviewed the owners of farms location, number of pig, onset date, clinical signs, farm management, movement, etc..

28. Methodology: Laboratory study • Collected serum, nasal swab and dead pigs specimens from every farm in infected area • Sent to Northeastern Veterinary Research and Development Center (Khon Kean province) and National Institute of Animal Health (Bangkok) • Sample will be tested by PCR technique for • PRRS • Classical Swine Fever Virus • Porcine Circovirus Type 2 • African Swine Fever • Bacterial culture

29. Clearly identifiable groups surveillance Laboratories Identify & count cases Obtain information Perform descriptive epidemiology

30. Identify & count cases • Identifying information • Demographic information • Clinical details • Risk factors Obtain information Perform descriptive epidemiology

31. Identify & count cases Obtain information Orient cases in - time - place - person (animal) Perform descriptive epidemiology

32. Cases Time Animal Place Evaluate information Pathogen? Transmission? Source?

33. Continuing common source Examples of epidemic curves:COMMON SOURCE Common source Point source Example: food contamination Example: Insecticide contamination

34. Example: Brucellosis outbreak among goat farms Examples of epidemic curves:PROPAGATED SOURCE

35. 10 9 8 7 6 5 4 3 2 1 0 Exposure period Estimation of “exposure period” by using Epidemic curve Point source outbreak Number of cases Disease A: Incubation period 7-10 days (from literature review) Median IP Min. IP Date of onset

36. Results

37. Descriptive results • An outbreak of PRRS in Silasubdistrict, and Bungneamsubdistrict, Muang • Silasub-district: • There were 28 small scale farms in village Moo. 13 and 14. • The infected farms were located too close to each other in 2 km. along the railway. • 23 farms had met suspect case definition (attack rate 82%) • 607 pigs died and 65 severe illness have been culling from 1,142 pigs population (mortality rate 57%)

38. Descriptive results • Bungneamsub-district: • 10 km. far from the Sila • Only one from 20 farms had met suspect case definition and confirmed PRRS. • The owner was brought his boars to Sila for natural breeding and bought growing pigs back to slaughter and sell in community.

39. Percentage of symptoms of PRRS cases in Muang district, Khon Kean province, August - November 2007 symptoms percentage

40. Number of PRRS infected farms by date of onset, Muang district, Khon Kean province, August – November 2007 No. of farms Bungneam subdistrict Sila subdistrict Onset date

41. Laboratory results

42. Laboratory results Autopsy • Lung congestion, mucous exudate • Brain congestion, edema • petechial hemorrhage at stomach • button ulcer at ileum • Lymph node congestion • pericarditis • petechial hemorrhage at kidneys Bacterial culture • Corynebacterium spp. 1/1 • Salmonellaspp. 1/1 • Mycoplasmahyopneumoniae 10/23 • Mycoplasmahyorhinis 1/6 • Pasteurellamultocida 1/1

43. Porcine Reproductive and Respiratory Syndrome (PRRS) • Infectious viral disease of swine, characterized by reproductive failure in sows and respiratory distress in piglets and growing pigs. • Easily transmitted through direct contact to susceptible pigs and vertically to fetuses. • Also know as Blue Ear Disease, Porcine Endemic Abortion and Respiratory Syndrome (PEARS) and Swine Infertility Respiratory Syndrome (SIRS). • Incubation period 5 – 20 days.

44. Porcine Reproductive and Respiratory Syndrome (PRRS) • Differential diagnosis • Swine fever • Porcine circovirus • Two 2 strains found in Thailand: US-strain (33.6%) & EU-strain (66.4%) (Thanawongnuwech et a, 2004) • The disease can be found in pig farms and hardly to eliminate because the virus can survive from 42 – 157 days after infected in different organs (Thanawongnuwech, 2005)

47. Farm management • Very low bio-security in Salasubdistrict • Almost of the farm connect to each other • 70% of the farms in Salasubdistrict used swill feeding from the market or restaurant • 74% of the farms bought weaning pig from unspecified sources • 65% of them breed their pig by using natural breeding services from other farms outside the community

48. Risk factors possible Sila district • Bought weaning pigs from unspecified sources • Swill feeding • Natural breeding • Farm to farm contamination

49. Develop hypotheses • What is the risk factor of this outbreak? • What is the disease causing the outbreak? • What is the source and the vehicle? • What is the mode of transmission? Compare hypotheses with facts

50. Test specific hypotheses Analytical epidemiological studies Case-control Cohort