Outbreak (Kt)[1]

8/8/2019 Outbreak (Kt)[1]

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OutbreakInvestigation

Dr. Kyaw ThuDr. Kyaw Thu

Community MedicineCommunity Medicine


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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


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Epidemic Curves and Types ofOutbreaks

Three types of outbreaks:(1) Common-source

Results from exposure of a susceptible

group of people to a common agent ofdisease

Further classifications:(a) Point source outbreak

(b) Continuing source outbreak(c) Intermittent source outbreak

(2) Propagated

(3) Mixed


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Point Source Outbreak

Duration of exposure to the common agent isrelatively brief and essentially simultaneous amongthose exposed

Epidemic curveExplosive nature

rises and fall rapidly without secondary waves

Short-lived

All cases develop disease within one incubationperiod of disease


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NUM

BE

ROF

NEW

CASES

INDEX CASE OR

COMMON EXPOSURE

MEDIAN INCUBATION PERIOD

TIME

EPIDEMIC CURVE POINT SOURCE INFECTION


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Continuing Source Outbreak

Exposure to the common agent of disease is

prolonged beyond a brief period

Exposure is not always due to exposure of infectious

agent (e.g. contamination or pollution) Epidemic curve

Rapid rise in # of cases

Reach a plateau

Followed by gradual decline

Last longer than time range of incubation period


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Intermittent Source Outbreak

Exposure to the common source of

disease is irregular

Epidemic curve

Small clusters or individual cases spread over

a relatively protracted time period

Can see gaps


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(2) Propagated Outbreaks

Progressive outbreak that usually is due to

direct person-to-person transmission of

disease

Via touching, sneezing, coughing, sexual relations

Or by indirect transmission through a vector

capable of transmitting an agent of disease to

a susceptible host

Animal source fly, mosquito, or rodent


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Propagated Outbreaks

Epidemic curve Person-to-person

Relatively gradual rise in case #

Tail off over a much longer period of time

May be more than 1 peak Separated by distances approximately = in length to

the average incubation period

Additional peaks represent secondary and tertiary

spread of disease

Tend to show longer duration than those forcommon-source outbreaks

Depends on the herd immunity of population


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NUMBE

ROF

NEW

CASES

INDEX CASE OR

COMMON EXPOSURE

MEDIAN INCUBATION PERIOD

TIME

EPIDEMIC CURVE PROPAGATED EPIDEMIC


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(3) Mixed Outbreaks

Combination of common source and

propagated outbreaks

Often begin with common source exposure

that is followed by person-to-person spread

Epidemic curve

Single large peak

Subsequent smaller peaks


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Determinants of Disease

Outbreaks

Amount of disease in a population

depends on:

# of people in population that are susceptible

(at risk)

# of people immune (not at risk)

all immune (Herd immunity)no epidemic


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OBJECTIVES OF OUTBREAKINVESTIGATIONS

To control continuing outbreaks

To prevent future outbreaks

To provide statutorily mandatedservices

To strengthen surveillance at locallevel

To advance knowledge about a

disease


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SPECIFIC DEMANDS WHENINVESTIGATING OUTBREAKS

Unexpected event

Need to act quickly

Need for rapid controlWork carried out in the

field

Systematicapproach


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STEPS OF AN OUTBREAKINVESTIGATION

1.Confirm outbreak and diagnosis

2.Case definition and identification

3.Descriptive data collection andanalysis

4.Develop hypothesis

5.Analytical studies to testhypothesis

6.Special studies

7.Implementation of controlmeasures


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Routinesurveillance

Clinical/Laboratory

General publicmedia

Detection

Is this an outbreak?

Diagnosis verified?

Clinical & laboratory link betweencases?

Expected numbers?


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Sequence of events in outbreak detection and confirmation(I

0

10

20

30

40

50

60

70

80

90

Days

Case

s

1st wk 2nd wk 3rd wk 4th wk 5th wk

Primary

Case1st case

at HC

Report

to DHO

Samples

taken

Lab:

result

Response

begins

Opportunities

for control


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Sequence of events in outbreak detection and

comfirmation (II)

0

20

40

60

80

100

120

Da s

Cases

1st wk 2nd wk 3rd wk 4th wk 5th wk

Primary

Case

1st case

at HCReport

to DHOLab:

result

Responsebegins

Potential

casesprevented

Samples

taken


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Outbreakconfirmed

Immediate control

measures?

Further

investigations?

Prophylaxis

Exclusion/isolationPublic warning

Hygienic measures

Unknown aetiology

(pathogen/source/transmission)

Cases serious

Cases still occurring

Public pressure

Training opportunity

Scientific interest

Assistance?


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Assistance?Epidemiologist

MicrobiologistEnvironmental

specialist

Ministry/Government

Press officer

Others

OutbreakInvestigation

Team?

FIELD


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Epidemiology

Clinicians

Education Laboratory

Coordination

Investigation

Surveillance

Prediction

Vector/reservoir

Dead Sick

Exposed

Health

personnel

Special

groups

General

population

Specimen

transfer

Clinical

Diagnostic

Media

Authorities

Decisions

Infrastructure

Regulations

Vaccination,

etc.


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Assistance?

Epidemiologist

Microbiologist

Environmentalspecialist

Ministry/Government

Press officer

Others

Outbreak

Investigation

Team?

Assess situation

Examine availableinformation

Preliminary hypothesis?

Case definition

Case finding

Descriptiveepidemiology


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CASE DEFINITION

Standard set of criteria for decidingif a

person should be classified assuffering

from the disease underinvestigation.

Clinical criteria, restrictions of time,

place, person.


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CASE DEFINITION:EXAMPLE

Patient older than 5 yearswith

severe dehydration or dyingof

acute watery diarrhoea intown

" "


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CASEDEFINITION:CATEGORISATION Possible

Patient with severe diarrhoea

Probable

Patient older than 5 years withsevere dehydration or dying of acutewatery diarrhoea in town "X" between

1st

and 10th June 2008 Confirmed

Isolation ofVibriocholerae from

stool of patient


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Identify &

count cases

Obtain

information

Perform

descriptive

epidemiology

Clearly identifiablegroups

Hospitals

Laboratories

Schools

Work place, etc.


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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


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Cases

Time

Place

Person

Evaluate

Information

Pathogen? Source? Transmissio

n?


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Develop hypothesis

Compare hypothesis withfacts

Who is at risk of becoming ill?

What is the disease causing the

outbreak? What is the source and the vehicle?

What is the mode of transmission?


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Test specific

hypothesis

Analytical epidemiological

studies

Cohort Case-control


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Implement controlmeasures

Control the source of the pathogen

Interrupt transmission

Modify host response

Prevent recurrence

May occur at any time during the

outbreak


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CONTROL THE SOURCE OF

PATHOGEN

Remove source of contaminationRemove persons from exposure

Inactive/neutralize the pathogenIsolate and/or treat infected

person


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INTERRUPT TRANSMISSION

Interrupt environmentalsources

Control vector transmission

Improve personal sanitation


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MODIFY HOST RESPONSE

Immunize susceptibles

Use prophylactic

chemotherapy


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Source/transmission

Investigation

+Control +++

Investigation

+++Control +

Investigation+++

Control +++

Investigation+++

Control +

Known Unknown

Kno

wn

Un

kn

ow

n

Ae

tio

logy


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AT THE END

Prepare written report

Communicate public healthmessages

Influence public health policy

Evaluate performance


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COMMUNICABLE DISEASE CONTROLIN MALAYSIA

1971 Epidemiology unit in MOH

Fully operational in 1996

Prevention and control of Infectiousdisease act 1988 for notification ofcommunicable diseases

25 notifiable diseases (9 by phone)and kept under surveillance


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Notification by phone(within 24 hours)

1. Dengue Fever

2. Yellow Fever

3. Diphtheria

4. Ebola

5. Food Poisoning

6. Cholera

7. Plague

8. Poliomyelitis

9. Rabies

Written Notification (within a


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Written Notification (within aweek)

1. Whooping Cough 11. Typhoid and

Paratyphoid2. Measles 12.Typhus and other

ricketsioses

3. Dysentery 13.Tuberculosis

4. Gonococcal Infection 14.Viral Encephalitis

5. Leprosy 15.Viral Hepatitis

6. Malaria 16.HIV

7. Myocarditis 17.Other Life threateninginfections

8. Relapsing Fever

9. Syphilis


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Summary

What is Outbreak?

Types of outbreaks?

Why outbreaks need to beinvestigated?

Detail steps in investigation of

outbreak? Notifiable diseases and diseases kept

under surveillance in Malaysia


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THANK YOU

Documents

Outbreak (Kt)[1]