Transcript IDSP Module 8

Outbreak investigation,
response and control
Integrated Disease Surveillance Programme (IDSP)
district surveillance officers (DSO) course
Preliminary questions to the group
• What is your experience in outbreak
investigations?
• If yes, what difficulties did you face?
• What would you like to learn about outbreak
investigations?
2
Outline of the session
1.
2.
3.
4.
Outbreaks and epidemics
Outbreak detection
Outbreak investigation
Managerial aspects of outbreak
investigations
3
Endemic versus epidemic
• Endemicity
 Disease occurring in a population regularly at a
usual level
• Tuberculosis, Malaria
• Epidemics
 Unusual occurrence of the disease in excess of its
normal expectation
• In a geographical location
• At a given point of time
e.g. Hepatitis E, measles, cholera
4
Outbreaks
Outbreaks versus epidemics
• Occurrence of cases of an illness in excess of
expected numbers
• Scale
 Outbreak
• Limited to a small area, within one district or few blocks
 Epidemic
• Covers larger geographic areas
• Linked to control measures in district/state
 No exact precise threshold: Use a word or the other
according to whether you want to generate or deflect
attention
• Be aware of legal implications of the use of the term
“Epidemic” in India (Epidemic disease act, being revised)
5
Outbreaks
Sources of information
to detect outbreaks
• Event-based surveillance
 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
• Case-based surveillance
 Review of routine surveillance data and triggers
6
Detection
Early warning signals for an outbreak
•
•
•
•
•
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 disease with outbreak
potential
 (e.g., Measles, Cholera, Dengue, Japanese encephalitis or
plague)
•
•
•
•
Unusual isolate (Cholera O 139)
Shifting in age distribution of cases (Cholera O 139)
High vector density
Natural disasters
7
Detection
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
8
Detection
The rapid response team
• Composition
 Epidemiologist, clinician and microbiologist
• Entomologist when vector-borne disease
 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
9
Detection
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
10
Investigations
The balance between investigation and
control while responding to an outbreak
Source / transmission
Known
Etiology Known
Control +++
Investigate +
Unknown Control +++
Investigate +++
11
Unknown
Control +
Investigate +++
Control +
Investigate +++
Investigations
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
12
Investigations
Step 1: Verifying the outbreak
• Validate the source of information
? Change in the reporting system
? Change in the population size
? Acute reporting of old, chronic cases
• Check with the concerned medical officer:
?
?
?
?
?
Abnormal increase in the number of cases
Clustering of cases
Epidemiological link between cases
Triggering event
Deaths
13
Investigations
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 (Descriptive
epidemiology)
? Does the hypothesis fits the fact
 YES: Propose control measures
 NO: Conduct analytical studies
14
Investigations
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
15
Hypothesis does not fit the facts:
-> Analytical investigations
Example: Outbreak of acute hepatitis (E)
in Baripada, Orissa, 2003
• Identification of a cluster of acute hepatitis
cases
• Diagnosis: HEV infection
• Use time, place and person analysis of
surveillance data to suggests hypotheses
16
Time: A cluster a month after a strike in the water treatment centre
Cases of acute hepatitis (E) by date of
onset, Baripada, January-March 2004
Investigation
started
45
Cases
Deaths
35
Strike among
municipal
Workers: Water
treatment stopped
30
25
20
15
10
5
3/7/04
3/5/04
3/3/04
3/1/04
2/28/04
2/26/04
2/24/04
2/22/04
2/20/04
2/18/04
2/16/04
2/14/04
2/12/04
2/10/04
2/8/04
2/6/04
17
2/4/04
2/2/04
1/31/04
1/29/04
1/27/04
1/25/04
1/23/04
1/21/04
1/19/04
1/17/04
1/15/04
1/13/04
1/11/04
1/9/04
1/7/04
1/5/04
1/3/04
0
1/1/04
Number of cases and deaths
40
Investigations
Place: Highest rates next to the pump taking water from river bed
Attack rate of acute hepatitis (E) by
residence, Baripada, Orissa, India, 2004
Attack rate
0 - 0.9 / 1000
1 - 9.9 / 1000
10 -19.9 / 1000
20+ / 1000
Underground water supply
18
Pump from river bed
Investigations
Person: Attack rate compatible with HEV
Attack rate of acute hepatitis (E) by age
and sex, Baripada, Orissa, India, 2004
Cases
Age
Sex
Population
Attack rate
per 1000
1012
0.1
0-4
1
5-9
11
21802
2
10-14
37
74004
5
15-44
416
51358
81
45+
73
56153
13
Male
341
102683
3.3
Female
197
101646
1.9
19
Investigations
What hypotheses would you generate for
the outbreak of acute hepatitis (E)
in Baripada, Orissa, 2003?
• Time:
 It happens a month after a strike in the water
treatment plant
• Place:
 It is clustered around a water source that takes
water from the river
• Person:
 Adults are mostly affected
The river water may have been supplied untreated in the area of the
outbreak because of the strike at the water treatment plant
20
Descriptive versus analytical
investigations
• Descriptive investigations
 Based upon cases only
 Look at time, place and person epidemiology
 Raise hypotheses
• Analytical investigations
 Based upon a study of the cases and non-cases
 Compare:
• Cases with controls with respect to exposure
• Exposed with unexposed with respect to incidence
 Test hypotheses
• How could we test the hypothesis for the Baripada
investigation?
21
Investigations
Steps of a full outbreak investigation
using analytical epidemiology to identify
the source of infection
1.
2.
3.
4.
5.
6.
7.
8.
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)
22
Consumption of pipeline water among
acute hepatitis (E) cases and controls,
Baripada, Orissa, India, 2004
Acute
hepatitis
Control
Total
Drunk water from river bed pump
493
134
627
Did not drink pump water
45
404
449
Total
538
538
1076
92% of cases (493/538) drunk water from
suspected source versus 25% (134/538) of controls
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
23
Investigations
3. Monitoring the situation
•
•
•
•
Trends in cases and deaths
Implementation of containment measures
Stocks of vaccines and drugs
Logistics
 Communication
 Vehicles
• Community involvement
• Media response
24
Investigations
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
25
Investigations
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
26
Investigations
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)
27
Management
Managerial aspects of outbreak response
• Logistics





Human resources
Medicines
Equipment and supplies
Vehicle and mobility
Communication channels
• Information, education and communication
• Media
 Daily update
28
Management
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
29
Management
Take home messages
1. Do not ignore or hide outbreaks
2. Respond to early warning signals
3. Investigate outbreaks to:


Control the current outbreak
Learn about the disease in the local setting
4. Outbreaks require an organized, well
managed response
30
Additional reading
• CDC text book on principles of epidemiology
• Section 5 of operations manual
• Module 8 of training manual
31
Detection