Outbreak (Kt)[1]
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Transcript of 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