Karoon Chanachai Bureau of Disease Control and Veterinary Service Department of Livestock Development Thailand 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 fo ID: 935631
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Slide1
Principles of Outbreak invEstigation
Karoon ChanachaiBureau of Disease Control and Veterinary ServiceDepartment of Livestock Development, Thailand
Slide2An 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
Slide3An 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.
Slide4Do we think this is an outbreak?, why?
Will we do anything after receiving this report ?
Slide5Definition of outbreakOccurrence 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 ?
Slide6Excess of Expected LevelMore than
Median number of cases in previous 5 years orAverage number of cases + 2sd of previous 5 yr
Slide7A 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.
Judged to be an outbreak
Slide8What?
Who?When?Where?
Why?
How
to react
?
Descriptive epidemiology
Analytical epidemiology
Epidemiology for action
Slide9Specific demands when investigating outbreaks
Unexpected event Need to act quickly Need for rapid control
Work carried out in the field
Systematic approach
Slide10Unexpected event
!!!
Slide11Steps of an outbreak investigation
Prepare for field workEstablish the existence of an outbreak Verify the diagnosisConstruct a working case definitionFind case systematically and record information
Perform descriptive epidemiologyDevelop hypothesis
Analytical studies to test hypotheses
Special studies (e.g. environmental study)
Implementation of control measures
Communication, including outbreak report
Slide12Is this an outbreak?
Diagnosis verified ?
clinical + laboratory
Link between cases?
Expected numbers?
Detection
Routine surveillance
Clinical / Laboratory
General public
Media
Slide13Sequence of events in outbreak detection and confirmation (I)
Primary
Case
1st
cases
notified
by Local
officer
Report
Lab
result
Samples
taken
Response
begins
DAY
CASES
Opportunity
for control
Slide14Sequence of events in outbreak detection and confirmation (II)
Prim
Noti
Rep
Lab
Samp
Response
begins
DAY
CASES
Potential
cases prevented
Slide15Outbreak confirmed
Further
investigation?
Immediate control
measures?
Slide16Unknown aetiology
(pathogen/source/transmission)
Cases seriousCases still occurring
Public pressure
Training opportunity
Scientific interest
Outbreak confirmed
Further
investigation?
Prophylaxis
Quarantine
/ isolation
Public warning
Hygienic
measures
Surveillance
Assistance ?
Immediate control
measures?
Slide17Epidemiologist
MicrobiologistEnvironmental specialistMinistry / GovernmentPress officerOthers
FIELD
Outbreak Investigation Team?
Slide18
Slide19Preparing for field works
Team members and rolesNecessary Knowledge and equipments; specimen collection & transport method, etc.Lines of communication
Slide20An 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.
Slide21Review 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.
……………….
………………
………………
Slide22Outbreak Investigation Team?
Epidemiologist
Microbiologist, Pathologist
Environmental specialist
Ministry / Government
Press officer
Others
Descriptive epidemiology
Assess situation
Examine available information
Preliminary hypothesis ?
Case definition
Case finding
Slide23(Passive cases)
(Active cases)
Reported cases
Cases in community (active cases)
Mild or no symptom
Treated by owner
Self recovering
Death
These cases can be potential spreader
Slide24Case definitionStandard 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, personUnit of interest
Simple, practical, objectiveSensitivity
Slide25Case 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
Slide26Case definition: categorisationSuspect
Farm that met suspect case definitionConfirmed
The confirmed farm was defined having at least one of pig positive to ………
Slide27Methodology: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..
Slide28Laboratory study Collected serum, nasal swab and dead pigs specimens from every farm in infected areaSent to Northeastern Veterinary Research and Development Center (
Khon Kean province) and National Institute of Animal Health (Bangkok)Sample will be tested by PCR technique forPRRSClassical Swine Fever VirusPorcine Circovirus
Type 2African Swine Fever Bacterial culture
Methodology
:
Slide29Identify & count cases
Obtain information
Perform descriptive epidemiology
Clearly identifiable groups
surveillance
Laboratories
Slide30Identify & count cases
Obtain information
Perform descriptive epidemiology
Identifying information
Demographic information
Clinical details
Risk factors
Slide31Identify & count cases
Obtain information
Perform descriptive epidemiology
Orient cases in
- time
- place
-
person (animal)
Slide32Animal
Place
Time
Cases
Evaluate information
Pathogen?
Source?
Transmission?
Slide33Point source
Continuing common source
Example:
food contamination
Example:
Insecticide contamination
Examples of epidemic curves:
COMMON SOURCE
Common source
Slide34Example: Brucellosis
outbreak among
goat
farms
Examples of epidemic curves:
PROPAGATED SOURCE
Slide35Disease A: Incubation period 7-10 days
(from literature review)Estimation of “exposure period”
by using Epidemic curve
Number of cases
Date of onset
Point source outbreak
Min. IP
Median IP
0
1
2
3
4
5
6
7
8
9
10
Exposure period
Slide36Results
Slide37Descriptive 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%)
Slide38Descriptive 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.
Percentage of symptoms of PRRS cases in Muang district,
Khon Kean province, August - November 2007
symptoms
percentage
Slide40Number of PRRS infected farms by date of onset, Muang district,
Khon Kean province, August – November 2007
Onset date
No. of farms
Sila
subdistrict
Bungneam subdistrict
Slide41Laboratory results
Places
Results
(
positive
/
specimens
)
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
Slide42AutopsyLung congestion, mucous
exudate Brain congestion, edemapetechial hemorrhage at stomachbutton 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
Laboratory results
Slide43Porcine 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.
Slide44Porcine Reproductive and Respiratory Syndrome (PRRS)
Differential diagnosisSwine feverPorcine 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)
Slide45Slide46Slide47Farm management Very low bio-security in Sala
subdistrictAlmost of the farm connect to each other70% of the farms in Sala subdistrict used swill feeding from the market or restaurant
74% of the farms bought weaning pig from unspecified sources65% of them breed their pig by using natural breeding services from other farms outside the community
Slide48Risk factors possible
Sila districtBought weaning pigs from unspecified sources Swill feeding Natural breeding
Farm to farm contamination
Slide49Develop hypotheses
Compare hypotheses with facts
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?
Slide50Case-control
Cohort
Analytical epidemiological studies
Test specific hypotheses
Slide51Limitations
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.
Slide52Conclusions 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
piglet’s carcass
1 month after outbreak
and all
pigs were
looked healthy
.
Slide53Recommendation
Treated mild cases and culling severe illness pigs to minimize lossQuarantine pigs in infected area for 4 monthsProhibit 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
Slide54Slide55Implement control measures
May occur at any time during the outbreak!!Prevent recurrence
Control the source of the pathogen
Interrupt transmission
Modify host response
Slide56Control the source of pathogenRemove source of contamination
Remove animal from exposureInactivate/ neutralise the pathogenIsolate and/or treat or cull infected animal
Slide57Interrupt transmissionInterrupt environmental sources
Control vector transmissionImprove sanitation
Slide58Modify host responseImmunise susceptible animal
Use prophylactic chemotherapy
Slide59At the endPrepare written report
Communicate Convince policyEvaluate performance
Slide60Steps of an outbreak investigation
Prepare for field workEstablish the existence of an outbreak Verify the diagnosisConstruct a working case definitionFind case systematically and record informationPerform descriptive epidemiology
Develop hypothesisAnalytical studies to test hypothesesSpecial studies (e.g. environmental study)
Implementation of control measures
Communication, including outbreak report
Implement control measures
Slide61Thank you