Outbreak investigation of epidemic diseases

Outbreak investigation

1. Outbreak investigation,
response and control
IDSP training module for state and
district surveillance officers
Module 8

2. 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

3. 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

4. Learning objectives (3/3)
•Outline the appropriate control measures to
be taken when the nature of the outbreak is
established:
Water borne diseases
Vector borne diseases
Vaccine preventable disease outbreaks
Outbreaks of unknown etiology

5. 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)

6. 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

7. 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

8. 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

9. 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 meningitis, measles
•Unusual isolate
•Shifting in age distribution of cases
•High vector density
•Natural disasters

10. Objectives of an outbreak investigation
1.Verify
2.Recognize the
magnitude
3.Diagnose the agent
4.Identify the source and
mode of transmission
5.Formulate prevention
and control measures
Host
Environment Agent
An outbreak comes from a change
in the way the host, the environment
and the agent interact:
This interaction needs to be understood
to propose recommendations

11. 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)

12. 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

13. Levels of response to different triggers
TriggerSignificance 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

14. 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

15. 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

16. The balance between investigation and
control while responding to an outbreak
Source / transmission
Known Unknown
EtiologyKnown Control +++
Investigate +
Control +
Investigate +++
UnknownControl +++
Investigate +++
Control +
Investigate +++

17. Steps in outbreak response
1.Verifying the outbreak
2.Sending the rapid response team
3.Monitoring the situation
4.Declaring the outbreak over
5.Reviewing the final report

18. 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:
?Abnormal increase in the number of cases
?Clustering of cases
?Epidemiological link between cases
?Occurrence of some triggering event
?Occurrence of deaths

19. 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

20. Yes
-> Control measures
Hypothesis fit the facts:
-> Control measures
Hypothesis does not fit the facts:
-> Further studies
Time, place person description
Formulation of hypothesis
No
-> Clinical, microbiological
and epidemiological investigation
Yes
-> Are the source and
modes of transmission
known?
No
Unusual event:
Is this an outbreak?
Investigating an outbreak

21. Acute hepatitis by week of onset in 3
villages, Bhimtal block, Uttaranchal, India,
July 2005
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May June July AugustSeptember
Week of onset
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Outlying case-
patient might have
been a source
Time

22. Incidence of acute hepatitis
by source of water supply, Bhimtal block,
Uttaranchal, India, July 2005
Mehragaon
main
village
Dov
Water supply
Spring
Reservoir
Pipeline
Attack rate
< 5%
5-9%
10% +
Mehragaon
Hydle colony
Chauriagaon
Mehragaon
Suspected
spring
Place

23. Incidence of acute hepatitis by age and sex in 3
villages, Bhimtal block, Uttaranchal, India,
July 2005
PopulationCases 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%
Sex Male 724 115 16%
Female 514 90 17%
Total 1238 205 16%
Person

24. When to ask for assistance
from the state level?
•Unusual outbreak
•High case fatality ratio
•Unknown etiology
•Trigger level three and above

25. Steps of a full outbreak investigation
using analytical epidemiology to identify
the source of infection
1.Determine the existence of an outbreak
2.Confirm the diagnosis
3.Define a case
4.Search for cases
5.Generate hypotheses using descriptive findings
6.Test hypotheses based upon an analytical study
7.Draw conclusions
8.Compare the hypothesis with established facts
9.Communicate findings
10.Execute prevention measures
Requires assistance from qualified field epidemiologist (FETP)

26. Cohort to estimate the risk of hepatitis
by water supply, Mehragaon village,
Uttaranchal, India, July 2005
CasesTotalIncidence
Relative risk
(95% C. I.)
Use of
water from
suspected
spring to
drink
No 12 143 9.2% Reference
Partially 13 94 13.8%1.6 (0.8-3.4)
Exclusively 152 529 28.7%3.4 (2.0-6.0)
C.I.: Confidence interval
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

27. 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

28. 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

29. 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

30. Managerial aspects of outbreak response
•Logistics
Human resources
Medicines
Equipment and supplies
Vehicle and mobility
Communication channels
•Information, education and communication
•Media
Daily update

31. 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

32. Specific outbreak control measures
•Waterborne outbreaks
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

33. Reports
•Preliminary report by the nodal medical
officer (First information report)
•Daily situation update
•Interim report by the rapid response team
•Final report

34. Points to remember
1.Outbreaks cause suffering, bad publicity and cost resources
2.Constant vigil is needed
3.Prompt timely action limits damage
4.Emphasis is on saving lives
5.Don’t diagnose every case once the etiology is clear
6.Management of linked cases does not require confirmation
7.The development of an outbreak is followed on a daily basis
8.Effective communication prevents rumours
9.Use one single designated spoke person
10.Learn lessons after the outbreak is over