PRINCIPLES OF OUTBREAK INVESTIGATION Karoon Chanachai Bureau of Disease Control and Veterinary...
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Transcript of PRINCIPLES OF OUTBREAK INVESTIGATION Karoon Chanachai Bureau of Disease Control and Veterinary...
PRINCIPLES OF OUTBREAK INVESTIGATION
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 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
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.
DO WE THINK THIS IS AN OUTBREAK?,
WHY?
Will we do anything after receiving this report ?
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 th
e
level of e
xpected ?
Excess of Expected Level
More than • Median number of cases in previous 5
years or• Average number of cases + 2sd of
previous 5 yrN u m b e r o f D is e a s e A c a s e s b y m o n t h , P r o v in c e X
0
1 0
2 0
3 0
4 0
5 0
6 0
7 0
J a n F e b M a r A p r M a y J u n J u l A u g S e p O c t N o v D e c
# c
as
es
2 0 0 3 M e d ia n 1 9 9 8 - 2 0 0 2
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.
Judged to be an outbreak
What? Who?When?Where?
Why?
How to react?
Descriptive epidemiology
Analytical epidemiology
Epidemiology for action
Specific demands when investigating outbreaks
• Unexpected event• Need to act quickly• Need for rapid control• Work carried out in the field
Systematic approach
Unexpected event !!!
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
Is this an outbreak?
Diagnosis verified ? clinical + laboratory
Link between cases?Expected numbers?
DetectionRoutine surveillanceClinical / LaboratoryGeneral publicMedia
Sequence of events in outbreak detection and confirmation (I)
0
10
20
30
40
50
60
70
80
90
PrimaryCase
1st casesnotified by Local
officerReport Lab
resultSamples
takenResponse
begins
DAY
CASES Opportunity for control
0
10
20
30
40
50
60
70
80
90
Sequence of events in outbreak detection and confirmation (II)
Prim Noti Rep LabSampResponse
begins
DAY
CASES
Potential cases prevented
Outbreak confirmed
Further investigation?
Immediate control measures?
Unknown aetiology(pathogen/source/transmission)Cases seriousCases still occurringPublic pressureTraining opportunity Scientific interest
Outbreak confirmed
Further investigation?
ProphylaxisQuarantine / isolationPublic warningHygienic measuresSurveillance
Assistance ?
Immediate control measures?
EpidemiologistMicrobiologistEnvironmental specialistMinistry / GovernmentPress officerOthers
FIELD
Outbreak Investigation
Team?
Preparing for field works
• Team members and roles
• Necessary Knowledge and equipments;
specimen collection & transport method,
etc.
• Lines of communication
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.
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.
……………….
………………
………………
Outbreak Investigation
Team?
EpidemiologistMicrobiologist, PathologistEnvironmental specialistMinistry / GovernmentPress officerOthers
Descriptive epidemiology
Assess situationExamine available information
Preliminary hypothesis ?Case definition
Case finding
(Passive cases)
(Active cases)
Reported cases
Cases in community (active cases) • Mild or no symptom
• Treated by owner
• Self recovering • DeathThese cases can be potential spreader
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
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
Case definition: categorisation
Suspect Farm that met suspect case definition
Confirmed The confirmed farm was defined having at least
one of pig positive to ………
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..
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
Methodology:
Identify & count cases
Obtain information
Perform descriptive epidemiology
Clearly identifiable groups
surveillance
Laboratories
Identify & count cases
Obtain information
Perform descriptive epidemiology
Identifying information
• Demographic
information
• Clinical details• Risk factors
Identify & count cases
Obtain information
Perform descriptive epidemiology
Orient cases in
- time
- place
- person (animal)
Animal
Place
Time
Cases
0
5
10
15
20
25
1 2 3 4 5 6 7 8 9 10
0
200
400
600
800
1000
1200
0-4 '5-14 '15-44
'45-64
'64+
Age Group
Evaluate information
Pathogen? Source? Transmission?
Point source
0
5
10
15
20
Continuing common source
Example: food contaminationExample: Insecticide contamination
Examples of epidemic curves:
COMMON SOURCE
0
1
2
3
4
5
6
7
8
9
10
Common sourc
e
Example: Brucellosis outbreak among goat farms
0
5
10
15
20
25
30
Examples of epidemic curves:
PROPAGATED SOURCE
Disease 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
RESULTS
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%)
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.
Percentage of symptoms of PRRS cases in Muang district, Khon Kean province, August - November 2007
0 10 20 30 40 50 60 70 80 90 100
abortion
seizure
petechial hemorrhage
cyanosis at ears
diarrhea
respiratory distress
symptoms
percentage
Number of PRRS infected farms by date of onset, Muang district, Khon Kean province, August – November 2007
0
1
2
3
4
5
6
18 -
24 ju
l
25 -
31 ju
l
1 - 7
aug
8 - 1
4 aug
15 -
21 a
ug
22 -
28 a
ug
29 a
ug - 4
sep
5 - 1
1 sep
12 -
18 s
ep
19 -
25 s
ep
26 s
ep -
2 oc
t
3 - 9
oct
10 -
16 o
ct
17 -
13 o
ct
24 -
30 o
ct
31 o
ct - 6
nov
7 no
v - 1
3 nov
Onset date
No. of farms
Sila subdistrict
Bungneam subdistrict
Laboratory 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
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
Laboratory results
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.
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)
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
Risk factors possible
Sila district Bought weaning pigs from unspecified
sources Swill feeding Natural breeding Farm to farm contamination
Develop 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?
Case-controlCohort
Analytical epidemiological studies
Test specific hypotheses
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.
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 piglet’s carcass 1 month after outbreak and all pigs were looked healthy.
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
Implement control measures
May occur at any time during the outbreak!!
Prevent recurrence
Control the source of the pathogen
Interrupt transmission
Modify host response
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
Interrupt transmission
Interrupt
environmental
sources
Control vector
transmission
Improve
sanitation
Modify host response
Immunise susceptible animal
Use prophylactic chemotherapy
At the end
Prepare written report
Communicate
Convince policy
Evaluate performance
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
Imp
lemen
t con
tr ol m
easures
Thank you