Transcript IDSP Module 8

Outbreak investigation,
response and control
IDSP training module for state and
district surveillance officers
Module 8
Learning objectives (1/3)
• Define an outbreak/epidemic
• List the various ways of detecting an
outbreak/ epidemic
• List the modes of transmission of causative
agents of outbreaks
• Describe warning signs of an impending
outbreak
Learning objectives (2/3)
• Specify the operational threshold levels of diseases
under surveillance for outbreak investigations
• List the members of rapid response team in your
district
• Enumerate the situations when DEIT would be
initiated
• Describe the steps of epidemic investigation to
establish an outbreak and determine its etiology
Learning objectives (3/3)
• Outline the appropriate control measures to
be taken when the nature of the outbreak is
established:
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Water borne diseases
Vector borne diseases
Vaccine preventable disease outbreaks
Outbreaks of unknown etiology
Definition of an outbreak
• Occurrence in a community of cases of an
illness clearly in excess of expected numbers
• The occurrence of two or more
epidemiologically linked cases of a disease
of outbreak potential constitutes an
outbreak
 (e.g., Measles, Cholera, Dengue, Japanese
encephalitis, or plague)
Outbreak and epidemic:
A question of scale
• Outbreaks
 Outbreaks are usually limited to a small area
 Outbreaks are usually within one district or few blocks
• Epidemics
 An epidemic covers larger geographic areas
 Epidemics usually linked to control measures on a
district/state wide basis
• Use a word or the other according to whether you
want to generate or deflect attention
Endemic versus epidemic
• Endemicity
 Disease occurring in a population regularly at a
usual level
• Tuberculosis, Malaria
• Epidemics
 Unusual occurrence of the disease clearly in
excess of its normal expectation
• In a geographical location
• At a given point of time
Sources of information
to detect outbreaks
• Rumour register
 To be kept in standardized format in each institution
 Rumours need to be investigated
• Community informants
 Private and public sector
• Media
 Important source of information, not to neglect
• Review of routine data
 Triggers
Early warning signals for an outbreak
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Clustering of cases or deaths
Increases in cases or deaths
Single case of disease of epidemic potential
Acute febrile illness of an unknown etiology
Two or more linked cases of meningitis, measles
Unusual isolate
Shifting in age distribution of cases
High vector density
Natural disasters
Objectives of an outbreak investigation
Host
1. Verify
2. Recognize the
magnitude
3. Diagnose the agent
4. Identify the source
and mode of
Environment
Agent
transmission
An outbreak comes from a change
5. Formulate prevention in the way the host, the environment
and control measures
and the agent interact:
This interaction needs to be understood
to propose recommendations
Outbreak preparedness:
A summary of preparatory action
Formation of rapid response team
Training of the rapid response team
Regular review of the data
Identification of ‘outbreak seasons’
Identification of‘outbreak regions’
Provision of necessary drugs and materials
Identification and strengthening appropriate
laboratories
• Designation of vehicles for outbreak investigation
• Establishment of communication channels in
working conditions (e.g., Telephone)
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Basic responses to triggers
• There are triggers for each condition under
surveillance
• Various trigger levels may lead to local or
broader response
• Tables in the operation manual propose
standardized actions to take following
various triggers
• Investigations are needed in addition to
standardized actions
Levels of response to different triggers
Trigger
Significance
Levels of response
1
Suspected /limited outbreak
• Local response by health
worker and medical officer
2
Outbreak
• Local and district response
by district surveillance
officer and rapid response
team
3
Confirmed outbreak
• Local, district and state
4
Wide spread epidemic
• State level response
5
Disaster response
• Local, district, state and
centre
Importance of timely action: The first
information report (Form C)
• Filled by the reporting unit
• Submitted to the District Surveillance Officer
as soon as the suspected outbreak is verified
• Sent by the fastest route of information
available
 Telephone
 Fax
 E-mail
The rapid response team
• Composition
 Epidemiologist, clinician and microbiologist
 Gathered on ad hoc basis when needed
• Role
 Confirm and investigate outbreaks
• Responsibility
 Assist in the investigation and response
 Primary responsibility rests with local health staff
The balance between investigation and
control while responding to an outbreak
Source / transmission
Etiology Known
Unknown
Known
Unknown
Control +++
Control +
Investigate +
Investigate +++
Control +++
Investigate +++
Control +
Investigate +++
Steps in outbreak response
1.
2.
3.
4.
5.
Verifying the outbreak
Sending the rapid response team
Monitoring the situation
Declaring the outbreak over
Reviewing the final report
Step 1: Verifying the outbreak
• Identify validity of source of information to
avoid false alarm/a data entry error
• Check with the concerned medical officer:
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Abnormal increase in the number of cases
Clustering of cases
Epidemiological link between cases
Occurrence of some triggering event
Occurrence of deaths
Step 2: Sending the rapid response team
• Review if the source and mode of transmission are
known
• If not, constitute team with:
 Medical officer
 Epidemiologist
 Laboratory specialist
• Formulation of hypothesis on basis of the
description by time, place and person
? Does the hypothesis fits the fact
 YES: Propose control measures
 NO: Conduct special studies
Investigating an outbreak
Unusual event:
Is this an outbreak?
Yes
-> Are the source and
modes of transmission
known?
Yes
-> Control measures
No
No
-> Clinical, microbiological
and epidemiological investigation
Time, place person description
Formulation of hypothesis
Hypothesis fit the facts:
-> Control measures
Hypothesis does not fit the facts:
-> Further studies
Time
90
80
Outlying casepatient might have
been a source
70
60
50
40
May
June
July
Week of onset
August
1st week
4th week
3rd week
2nd week
1st week
4th week
3rd week
2nd week
1st week
4th week
2nd week
1st week
4th week
3rd week
2nd week
10
0
3rd week
30
20
1st week
Number of cases
Acute hepatitis by week of onset in 3
villages, Bhimtal block, Uttaranchal, India,
July 2005
September
Place
Incidence of acute hepatitis
by source of water supply, Bhimtal block,
Uttaranchal, India, July 2005
Dov
Mehragaon
main
village
Suspected
spring
Mehragaon
Hydle colony
Mehragaon
Chauriagaon
Water supply
Spring
Reservoir
Pipeline
Attack rate
< 5%
5-9%
10% +
Person
Incidence of acute hepatitis by age and sex in
3 villages, Bhimtal block, Uttaranchal, India,
July 2005
Population
Cases
Attack rate
Age
0-4
105
2
2%
(Years)
5-9
110
4
4%
10-14
134
23
17%
15-44
729
139
19%
45+
261
37
14%
Male
724
115
16%
Female
514
90
17%
1238
205
16%
Sex
Total
When to ask for assistance
from the state level?
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Unusual outbreak
High case fatality ratio
Unknown etiology
Trigger level three and above
Steps of a full outbreak investigation
using analytical epidemiology to identify
the source of infection
1.
2.
3.
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6.
7.
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9.
10.
Determine the existence of an outbreak
Confirm the diagnosis
Define a case
Search for cases
Generate hypotheses using descriptive findings
Test hypotheses based upon an analytical study
Draw conclusions
Compare the hypothesis with established facts
Communicate findings
Execute prevention measures
Requires assistance from qualified field epidemiologist (FETP)
Cohort to estimate the risk of hepatitis
by water supply, Mehragaon village,
Uttaranchal, India, July 2005
Cases
Use of
water from
suspected
spring to
drink
Total
Incidence
Relative risk
(95% C. I.)
No
12
143
9.2%
Reference
Partially
13
94
13.8%
1.6 (0.8-3.4)
152
529
28.7%
3.4 (2.0-6.0)
Exclusively
Analytical epidemiology compares cases and non cases or exposed
versus unexposed to test the hypothesis generated on the basis of
the time, place and person description
C.I.: Confidence interval
3. Monitoring the situation
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Trends in cases and deaths
Implementation of containment measures
Stocks of vaccines and drugs
Logistics
 Communication
 Vehicles
• Community involvement
• Media response
4. Declaring the outbreak over
• Role of the district surveillance officer /
Medical health officer
• Criteria
 No new case during two incubation periods since
onset of last case
• Implies careful case search to make sure no
case are missed
5. Review of the final report
• Sent by medical officer of the primary health
centre to the district surveillance officer /
medical and health officer within 10 days of
the outbreak being declared over
• Review by the technical committee
 Identification of system failures
 Longer term recommendations
Managerial aspects of outbreak response
• Logistics
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Human resources
Medicines
Equipment and supplies
Vehicle and mobility
Communication channels
• Information, education and communication
• Media
 Daily update
Control measures for an outbreak
• General measures
 Till source and route of transmission identified
• Specific measures, based upon the results of the
investigation
 Agent
• Removing the source
 Environment
• Interrupting transmission
 Host
• Protection (e.g., immunization)
• Case management
Specific outbreak control measures
• Waterborne outbreaks
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Access to safe drinking water
Sanitary disposal of human waste
Frequent hand washing with soap
Adopting safe practices in food handling
• Vector borne outbreaks
 Vector control
 Personal protective measures
• Vaccine preventable outbreaks
 Supplies vaccines, syringes and injection equipment
 Human resources to administer vaccine
 Ring immunization when applicable
Reports
• Preliminary report by the nodal medical
officer (First information report)
• Daily situation update
• Interim report by the rapid response team
• Final report
Points to remember
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10.
Outbreaks cause suffering, bad publicity and cost resources
Constant vigil is needed
Prompt timely action limits damage
Emphasis is on saving lives
Don’t diagnose every case once the etiology is clear
Management of linked cases does not require confirmation
The development of an outbreak is followed on a daily basis
Effective communication prevents rumours
Use one single designated spoke person
Learn lessons after the outbreak is over