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
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
Verify
Recognize the magnitude
Diagnose the agent
Identify the source and mode of transmission
Formulate prevention and control measures

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
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

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

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
Etiology
Control +++
Investigate +
Control +
Investigate +++

17. Steps in outbreak response
Verifying the outbreak
Sending the rapid response team
Monitoring the situation
Declaring the outbreak over
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. Investigating an outbreak

21. Outlying case-patient might have been a source
Time
Acute hepatitis by week of onset in 3 villages, Bhimtal block, Uttaranchal, India, July 2005 90
Outlying case-patient might have been a source 80 70 60
This graph represents the number of cases by week of onset between the month of May and September 2005 in the the tree villages.
The first case in the area developed an illness during the first week of May. The outbreak peaked during the fourth week of July – when the investigated began – and the number of cases decreased during the early part of the month of August. The shape of the curve suggested a common source outbreak.
You can see on this graph that before the outbreak, there were a number of initial cases that could be considered as index cases. 50
Number of cases 40 30 20 10
3rd week
1st week
1st week
2nd week
3rd week
4th week
1st week
2nd week
4th week
1st week
3rd week
4th week
1st week
3rd week
2nd week
2nd week
4th week
May
June
July
August
September
Week of onset

22. Place
Incidence of acute hepatitis by source of water supply, Bhimtal block, Uttaranchal, India, July 2005
Water supply
Spring
Reservoir
Pipeline
Attack rate
< 5%
5-9%
10% +
Dov
Mehragaon main village
This map shows the three villages where the outbreak was reported, including Mehragaon (that you can see on the right and on the centre), Chauriagon (that you can see at the bottom left of the slide) and Dov that you can see on the top left of the slide.
We represented each of these villages with a colour representing the attack rate on a yellow to red scale. The yellow denotes the lowest incidence and the red the highest incidence.
The blue elements on the slide represent the water supply system, including the springs, the reservoirs shown as blue rectangles and the pipelines shown as blue arrows.
As you can see, Dov that had its own spring had the lowest incidence in yellow. Chauriagon that shared a spring with Mehragon had an intermediate in orange and Mehragon that had almost only one source of water supply had the highest incidence in red. On the basis of the attack rate by villages, we generated the hypothesis that the spring that supplied both Mehragon and Chauriagon was the source of the outbreak.
Suspected spring
Mehragaon Hydle colony
Mehragaon
Chauriagaon

23. 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%
Sex
Male
724
115
16%
Female
514 90
Total
1238
205
This graph represents the incidence of acute hepatitis by age and sex in the 3 villages.
You can see that the attack rate was highest among persons 15 to 44 years of age (19%) followed by the 10 to 14 years of age (17 %) and by those 45 years of age or older (14 %). The lowest attack rate was found among children under 9 years of age. Female were slightly more affected than males.

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

25. Requires assistance from qualified field epidemiologist (FETP)
Steps of a full outbreak investigation using analytical epidemiology to identify the source of infection
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
E.g.; for practices associated with meth use
Requires assistance from qualified field epidemiologist (FETP)

26. Cohort to estimate the risk of hepatitis by water supply, Mehragaon village, Uttaranchal, India, July 2005
Cases
Total
Incidence
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 ( )
Exclusively
152
529
28.7%
3.4 ( )
To test this hypothesis, we conducted a cohort study in Mehragaon village to estimate the strength of the association between illness and the source of water supply.
The highest attack rate (28.7 %) was among the people using exclusively the suspected spring water.
There was an intermediate attack rate (13.8 %) among those who partially used the suspected spring water.
The lowest attack rate ( 9.2 %) was among those who never used the suspected spring water.
This association between illness and the suspected spring water, along with a dose response relationhsip suggested that the suspected springwas indeed the source of infection.
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

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
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