Transcript Outbreak investigation

PRINCIPLES OF OUTBREAK
INVISTIGATION
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
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
Two or more linked cases of the same illness
or
New diseases
Excess of Expected Level
More than
• Median number of cases in previous 5 years or
• Average number of cases + 2sd of previous 5 yr
Number of Disease A cases by month, Province X
70
60
# cases
50
40
30
20
10
0
Jan
Feb
Mar
Apr
2003
May
Jun
Jul
Aug
Sep
Oct
Median 1998 - 2002
Nov
Dec
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.
What? Who?
When?
Where?
Descriptive epidemiology
Why?
Analytical epidemiology
How to react?
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
Steps of an outbreak investigation
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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
Detection
Routine surveillance
Clinical / Laboratory
General public
Media
Is this an outbreak?
Diagnosis verified ?
clinical + laboratory
Link between cases?
Expected numbers?
Sequence of events in outbreak detection and
confirmation (I)
1st cases
notified
Primary by Local
Case
officer
Report Samples Lab Response
taken result begins
90
80
70
60
50
40
Opportunity
for control
30
20
DAY
39
37
35
33
31
29
27
25
23
21
19
17
15
13
11
9
7
5
3
10
0
1
CASES
Sequence of events in outbreak detection and
confirmation (II)
Prim Noti Rep Samp Lab
Response
begins
90
80
70
Potential
cases prevented
60
CASES 50
40
30
20
10
DAY
39
37
35
33
31
29
27
25
23
21
19
17
15
13
11
9
7
5
3
1
0
Outbreak confirmed
Immediate control
measures?
Further
investigation?
Outbreak confirmed
Immediate control
measures?
Prophylaxis
Quarantine / isolation
Public warning
Hygienic measures
Surveillance
Further
investigation?
Unknown aetiology
(pathogen/source/transmission)
Cases serious
Cases still occurring
Public pressure
Training opportunity
Scientific interest
Assistance ?
Epidemiologist
Microbiologist
Environmental specialist
Ministry / Government
Press officer
Others
Outbreak
Investigation
Team?
FIELD
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.
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……………….
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………………
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………………
Epidemiologist
Microbiologist, Pathologist
Environmental specialist
Ministry / Government
Press officer
Others
Outbreak
Investigation
Team?
Assess situation
Examine available information
Preliminary hypothesis ?
Case definition
Case finding
Descriptive epidemiology
Reported
cases
(Passive cases)
Cases in community
(Active(active
cases)
cases)
• Mild or no symptom
• Treated by owner
• Self recovering
• Death
These cases can be potential
spreader
Case definition
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Standard set of criteria for deciding if an individual
animal/flock should be classified as suffering from
the disease under investigation.
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Clinical criteria, restrictions of time, place, person
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Unit of interest
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Simple, practical, objective
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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
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Suspect
 Farm
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that met suspect case definition
Confirmed
 The
confirmed farm was defined having at least
one of pig positive to ………
Methodology:
Case finding
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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..
Methodology:
Laboratory study
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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
Identify &
count cases
Obtain information
Perform descriptive
epidemiology
Clearly identifiable groups
surveillance
Laboratories
Identify &
count cases
Identifying information
Obtain
information
• Demographic
information
• Clinical details
• Risk factors
Perform descriptive
epidemiology
Identify &
count cases
Obtain
information
Perform descriptive
epidemiology
Orient cases in
- time
- place
- person (animal)
Cases
Time
Animal
1200
Place
1000
800
25
20
15
600
10
400
200
5
0
0
0-4
'5-14 '1544
'4564
'64+
1
2
3
4
5
6
7
8
Age Group
Evaluate information
Pathogen?
Source?
Transmission?
9
10
Examples of epidemic curves:
COMMON SOURCE
10
9
8
7
6
5
4
Common
source
Point source
Continuing common source
20
3
2
1
0
15
10
5
19
16
13
10
7
4
0
1
Example: food contamination
Example: Insecticide contamination
Examples of epidemic curves:
PROPAGATED SOURCE
30
25
20
15
10
5
0
Example: Brucellosis outbreak among goat farms
Estimation of “exposure period”
by using Epidemic curve
Point source outbreak
Number of cases
10
9
8
7
6
5
4
3
2
1
0
Median IP
Disease A:
Incubation period 7-10 days
(from literature review)
Min. IP
Exposure period
Date of onset
RESULTS
Descriptive results
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An outbreak of PRRS in Sila subdistrict, and Bungneam
subdistrict, Muang
Sila sub-district:
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There were 28 small scale farms in village Moo. 13 and 14.
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The infected farms were located too close to each other in 2 km.
along the railway.
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23 farms had met suspect case definition (attack rate 82%)
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607 pigs died and 65 severe illness have been culling from 1,142
pigs population (mortality rate 57%)
Descriptive results
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Bungneam sub-district:
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10 km. far from the Sila
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Only one from 20 farms had met suspect case definition
and confirmed PRRS.
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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
respiratory distress
diarrhea
cyanosis at ears
petechial hemorrhage
seizure
abortion
0
10
20
30
40
percentage
50
60
70
80
90
100
Number of PRRS infected farms by date of onset, Muang
district, Khon Kean province,
August – November 2007
No. of farms
Sila
subdistrict
Bungneam subdistrict
6
5
4
3
2
1
25
18
-2
4
ju
-3 l
1
ju
1
-7 l
au
8
-1 g
4
15
au
-2 g
1
22
au
-2 g
29
8
au
au
g
g
-4
se
5
-1 p
12 1 s
e
-1 p
8
19
se
-2 p
26
5
se
se
p
p
-2
oc
t
3
-9
10
oc
-1 t
6
17
oc
-1 t
3
24
oc
-3 t
31
0
oc
oc
t
t7
no 6 n
o
v
-1 v
3
no
v
0
Onset date
Laboratory results
Places
Results
(positive/specimens)
PRRSV
CSFV
AFSV
PCV2
10/30
0/16
0/11
1/18
Bungnean subdistrict
1/3
0/1
-
0/1
Chumpae district
0/5
0/1
-
1/1
Sila subdistrict
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
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Bacterial culture
Corynebacterium spp.
 Salmonella spp.
 Mycoplasma hyopneumoniae
 Mycoplasma hyorhinis
 Pasteurella multocida
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1/1
1/1
10/23
1/6
1/1
Porcine Reproductive and Respiratory
Syndrome (PRRS)
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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)
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Differential diagnosis

Swine fever
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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
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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
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Develop hypotheses
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•
•
•
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
Test specific hypotheses
Analytical epidemiological studies
Cohort
Case-control
Limitations
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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
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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
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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!!
Control the source of the pathogen
Interrupt transmission
Modify host response
Prevent recurrence
Control the source of pathogen
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Remove source of contamination
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Remove animal from exposure
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Inactivate/ neutralise the pathogen
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Isolate and/or treat or cull infected animal
Interrupt transmission
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Interrupt
environmental sources
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Control vector
transmission
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Improve sanitation
Modify host response
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Immunise susceptible animal
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Use prophylactic chemotherapy
At the end
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Prepare written report
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Communicate
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Convince policy
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Evaluate performance
Steps of an outbreak investigation
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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
Thank you