Principles of Outbreak invEstigation

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Principles of Outbreak invEstigation

• Karoon Chanachai
• Bureau of Disease Control and Veterinary Service
• Department of Livestock Development, Thailand

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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

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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 Sila subdistrict, Muang district. Symptoms of
  infected pigs were fever, cough, blue ears, and
  petechial hemorrhage.

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Do we think this is an outbreak?, why?

• Will we do anything after receiving this report ?

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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 ?
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Excess of Expected Level

• More than
• Median number of cases in previous 5 years or
• Average number of cases 2sd of previous 5 yr

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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.
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Who? When? Where?
What?
Descriptive epidemiology
Why?
Analytical epidemiology
How to react?
Epidemiology for action
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Specific demands when investigating outbreaks

• Unexpected event
• Need to act quickly
• Need for rapid control
• Work carried out in the field

Systematic approach
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Unexpected event !!!
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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

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Routine surveillance Clinical /
Laboratory General public Media
Detection
Is this an outbreak?
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Sequence of events in outbreak detection and
confirmation (I)
1st cases notified by Local officer
Primary Case
Report
Lab result
Samples taken
Response begins
CASES
Opportunity for control
DAY
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Sequence of events in outbreak detection and
confirmation (II)
Response begins
Prim
Noti
Rep
Lab
Samp
Potential cases prevented
CASES
DAY
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Outbreak confirmed
Further investigation?
Immediate control measures?
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Outbreak confirmed
Further investigation?
Immediate control measures?
Unknown aetiology (pathogen/source/transmission) C
ases serious Cases still occurring Public
pressure Training opportunity Scientific interest
Prophylaxis Quarantine / isolation Public
warning Hygienic measures Surveillance
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Outbreak Investigation Team?
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?
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Preparing for field works

• Team members and roles
• Necessary Knowledge and equipments specimen
  collection transport method, etc.
• Lines of communication

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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 Sila subdistrict, Muang district. Symptoms of
  infected pigs were fever, cough, blue ears, and
  petechial hemorrhage.

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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.
• .

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Epidemiologist Microbiologist, Pathologist Environ
mental specialist Ministry / Government Press
officer Others
Outbreak Investigation Team?
Assess situation Examine available
information Preliminary hypothesis ? Case
definition Case finding
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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)
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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

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Case definition

• Suspect farm was defined as pig farm in village
  Moo.13 and surrounding villages, Sala
  subdistrict, 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

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Case definition categorisation

• Suspect
• Farm that met suspect case definition
• Confirmed
• The confirmed farm was defined having at least
  one of pig positive to

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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..

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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

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Clearly identifiable groups surveillance Laborator
ies
Identify count cases
Obtain information
Perform descriptive epidemiology
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Identify count cases

• Identifying information
• Demographic information
• Clinical details
• Risk factors

Obtain information
Perform descriptive epidemiology
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Identify count cases
Obtain information
Orient cases in - time - place - person
(animal)
Perform descriptive epidemiology
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Cases
Time
Animal
Place
Evaluate information
Pathogen?
Transmission?
Source?
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Examples of epidemic curvesCOMMON SOURCE
Common source
Point source
Example food contamination
Example Insecticide contamination
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Examples of epidemic curvesPROPAGATED SOURCE
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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

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Results
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Descriptive results

• An outbreak of PRRS in Sila subdistrict, and
  Bungneam subdistrict, Muang
• Sila sub-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)

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Descriptive results

• Bungneam sub-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.

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Percentage of symptoms of PRRS cases in Muang
district, Khon Kean province, August - November
2007
symptoms
percentage
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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
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Laboratory results
Places Results (positive/specimens) Results (positive/specimens) Results (positive/specimens) Results (positive/specimens)
Places PRRSV CSFV AFSV PCV2
Sila subdistrict 10/30 0/16 0/11 1/18
Bungnean subdistrict 1/3 0/1 - 0/1
Chumpae district 0/5 0/1 - 1/1
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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
• Salmonella spp. 1/1
• Mycoplasma hyopneumoniae 10/23
• Mycoplasma hyorhinis 1/6
• Pasteurella multocida 1/1

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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.

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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)

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Farm management

• Very low bio-security in Sala subdistrict
• Almost of the farm connect to each other
• 70 of the farms in Sala subdistrict 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

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Risk factors possible

• Sila district
• Bought weaning pigs from unspecified sources
• Swill feeding
• Natural breeding
• Farm to farm contamination

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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
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Test specific hypotheses
Analytical epidemiological studies
Case-control
Cohort
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Limitations

• Even though, control measures were fully
  implemented by local officer. Some owners had
  sold out their pigs to other areas after detected
  the abnormal signs without notification to the
  government officer.
• All of infected farms are located along the
  railway which posses to the State Railway of
  Thailand, so the owners did not want to change
  their life or improve their farms because it will
  cost expenses and other important point is they
  will be expel from this area anytime.

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Conclusions and Discussions

• PRRS outbreak occurred in small scale pig farms
  in Sila and Bungneam subdistrict, Muang district,
  Khon Kean Province.
• There will be co-infection of PRRSV, PCV type2
  and bacteria in this outbreak
• The virus can easily spread because we still
  found PRRSV in piglets carcass 1 month after
  outbreak and all pigs were looked healthy.

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Recommendation

• Treated mild cases and culling severe illness
  pigs to minimize loss
• Quarantine pigs in infected area for 4 months
• Prohibit to bring new piglets
• Pigs were allowed only movement to slaughterhouse
• Education to farm holders by group activities,
  recommended for farm holders to improve the farm
  sanitation to prevent outbreak in future

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Implement control measures
May occur at any time during the outbreak!!
Control the source of the pathogen
Interrupt transmission
Modify host response
Prevent recurrence
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Control the source of pathogen

• Remove source of contamination
• Remove animal from exposure
• Inactivate/ neutralise the pathogen
• Isolate and/or treat or cull infected animal

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Interrupt transmission

• Interrupt environmental sources
• Control vector transmission
• Improve sanitation

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Modify host response

• Immunise susceptible animal
• Use prophylactic chemotherapy

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At the end

• Prepare written report
• Communicate
• Convince policy
• Evaluate performance

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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

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Thank you