Principles of Outbreak invEstigation - PowerPoint Presentation

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Principles of Outbreak invEstigation

Karoon ChanachaiBureau of Disease Control and Veterinary ServiceDepartment 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 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 ?

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Excess of Expected LevelMore than

Median number of cases in previous 5 years orAverage number of cases + 2sd of previous 5 yr

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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

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What?

Who?When?Where?

Why?

How

to react

?

Descriptive epidemiology

Analytical epidemiology

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 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

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Is this an outbreak?

Diagnosis verified ?

clinical + laboratory

Link between cases?

Expected numbers?

Detection

Routine surveillance

Clinical / Laboratory

General public

Media

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Sequence 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

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Sequence of events in outbreak detection and confirmation (II)

Prim

Noti

Rep

Lab

Samp

Response

begins

DAY

CASES

Potential

cases prevented

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Outbreak confirmed

Further

investigation?

Immediate control

measures?

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Unknown 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?

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Epidemiologist

MicrobiologistEnvironmental specialistMinistry / GovernmentPress officerOthers

FIELD

Outbreak Investigation Team?

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

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Preparing for field works

Team members and rolesNecessary 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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Outbreak 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

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(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

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Case 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

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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: categorisationSuspect

Farm that met suspect case definitionConfirmed

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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Laboratory 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

:

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Identify & count cases

Obtain information

Perform descriptive epidemiology

Clearly identifiable groups

surveillance

Laboratories

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Identify & count cases

Obtain information

Perform descriptive epidemiology

Identifying information

Demographic information

Clinical details

Risk factors

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Identify & count cases

Obtain information

Perform descriptive epidemiology

Orient cases in

- time

- place

-

person (animal)

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Animal

Place

Time

Cases

Evaluate information

Pathogen?

Source?

Transmission?

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Point source

Continuing common source

Example:

food contamination

Example:

Insecticide contamination

Examples of epidemic curves:

COMMON SOURCE

Common source

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Example: Brucellosis

outbreak among

goat

farms

Examples of epidemic curves:

PROPAGATED SOURCE

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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

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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

Onset date

No. of farms

Sila

subdistrict

Bungneam subdistrict

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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

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AutopsyLung 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

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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 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)

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Farm 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

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Risk factors possible

Sila districtBought weaning pigs from unspecified sources Swill feeding Natural breeding

Farm to farm contamination

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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?

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Case-control

Cohort

Analytical epidemiological studies

Test specific hypotheses

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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

piglet’s 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 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

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Implement control measures

May occur at any time during the outbreak!!Prevent recurrence

Control the source of the pathogen

Interrupt transmission

Modify host response

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Control the source of pathogenRemove source of contamination

Remove animal from exposureInactivate/ neutralise the pathogenIsolate and/or treat or cull infected animal

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Interrupt transmissionInterrupt environmental sources

Control vector transmissionImprove sanitation

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Modify host responseImmunise susceptible animal

Use prophylactic chemotherapy

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At the endPrepare written report

Communicate Convince policyEvaluate performance

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Steps 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

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Thank you