INVESTIGATING A FEVER OUTBREAK - GUIDELINES

1. Investigating a fever outbreak
-An overview
 DR.M.K.SUDARSHAN MD(BHU),FAMS, HON.FFPH(UK)
 Advisory Board Member, Fever
Foundation
 Retd. Dean/Principal and Professor of
Community , Kempegowda Institute of
Medical Sciences, Bangalore

2. Definition of outbreak
 Occurrence 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 same
illness

3. Outbreaks: The basics
 Goals of an outbreak investigation:
 To identify the source of illness
 To guide public health intervention
 Ways to recognize an outbreak:
 Routine surveillance activities (IDSP, etc)
 Reports from clinicians and laboratories
 Reports from press and media

4. Objectives of outbreak
investigations
 To control ongoing outbreaks
 To prevent future outbreaks
 To provide statutorily mandated
services
 To strengthen surveillance at local level
 To advance knowledge about a disease
 To provide training opportunities

5. Steps of an outbreak
investigation
1. Verify the diagnosis and confirm the
outbreak
2. Define a case and conduct case
finding
3. Tabulate and orient data: time, place,
person
4. Take immediate control measures

6. Steps of an outbreak
investigation
5. Formulate and test hypothesis
6. Plan and execute additional studies
7. Implement and evaluate control
measures
8. Communicate findings

7. 1. Verify the diagnosis and
confirm the outbreak
 Confirm the diagnosis by laboratory
tests
 Rule out misdiagnoses or laboratory
errors
 Confirm the occurrence of outbreak ie.
occurrence of a number of cases clearly
in excess of normal expectancy
( compare it with the previous times)

8. 2. Define a case and conduct
case finding
 Develop a specific case definition using:
 Symptoms or laboratory results
 Time period
 Location
 Conduct surveillance using case definition
 Existing surveillance
 Active surveillance (e.g. community searches,
review medical records, etc.)
 Interview & examine cases-patients

9. 3. Tabulate and orient data
 Create line listing
 Person
 Who was infected/affected ?
 What do the cases have in common?
 Place
 Where were they infected/affected?
 May be useful to draw a map ( spot map )
 Time
 When were they infected/affected ?
 Draw an epidemic curve

10. Example of a Line Listing

11. Person
Place
Time
Cases
0
5
10
15
20
25
1 2 3 4 5 6 7 8 9 10
0
200
400
600
800
1000
1200
0-4 '5-14 '15-
44
'45-
64
'64+
Age Group
Evaluate information
Pathogen? Source? Transmission?

12. 0
5
10
15
20
25
1 3 5 7 9 11 13 15 17 19
0
5
10
15
20
1
4
7
10
13
16
19
0
5
10
15
20
1
3
5
7
9
11
13
15
17
19
Examples of
epidemic curves
Point source
Continuing common source Multiple waves -person to person or
further outbreak

13. Graphical Representation of an
Outbreak
Classic epi. curve

14. 3. Location
•Investigators can
calculate attack rates of
cases in different
locations.
•These can be places of
residence, places of
employment, sites of
exposure, etc.
•Locations with high
attack rates often
indicate the sources of
infection or
contamination.
•A spot map showing
the locations of cases
can give a very good
idea of the source.

15. 0
10
20
30
40
50
60
70
80
90
1
4
7
10
13
16
19
22
25
28
31
34
37
40
Sequence of Events in outbreak detection and
confirmation (I)
Primary
Case
1st case
at HC
Report
to DHO
Lab
result
Samples
taken
Response
begins
DAY
CASES
Opportunity
for control

16. 0
10
20
30
40
50
60
70
80
90
1
4
7
10
13
16
19
22
25
28
31
34
37
40
Sequence of events in outbreak detection and
confirmation (II)
PRIM HC REP RESSAMP
Response
begins
DAY
CASES
Potential
Cases Prevented

17. 4. Take immediate control
measures
 If an obvious source of the
contamination is identified…institute
control measures immediately!
 The Outbreak investigation team
consists of – 1. Epidemiologist 2.
Clinician 3. Public Health Personnel 4.
Microbiologist/Lab. personnel 5.Others

18. 5. Formulate and test
hypothesis
 Develop hypotheses
 literature reviews of previous outbreaks
 interviews of several case-patients
 Conduct an analytic study to test
hypotheses
 Retrospective cohort study
 Case-control study

19. 6. Plan and execute additional
studies
Environmental sampling
 Collect appropriate samples
 Allow epidemiological data to guide testing
 If analytic study results are conclusive,
don’t wait for positive samples before
implementing prevention

20. 7. Implement and evaluate
control measures
 Work with Directorate , and public
health personnel to institute control
measures
 Prevent further exposure and future
outbreaks by eliminating or treating the
source
 Create mechanism to evaluate both
short- and long-term success

21. Coordination
Epidemiology
Education
Clinicians
Laboratory
Media Authorities
Diagnostic
Clinical
Specimen
transfer
Dead Sick
Exposed
SurveillanceInvestigation
Prediction
Health
personnel
Special
groups
General
population
Decisions
Infrastructure
Regulations
Vaccinations etc
Vector
Reservoir

22. 8. Communicate findings
 Identify a single member of the
investigation team ( usually
epidemiologist ) to interact with media
and communicate progress and findings
 Summarize investigation, make
recommendations, and disseminate
report to all participants

23. Conclusions
 The steps listed for an outbreak investigation
comprise a brief introduction and rough
guide. Only by conducting investigations
repeatedly over an entire career will public
health professionals one can truly learn the
methods of outbreak investigations.
 Snow’s “shoe leather epidemiology” serves as
a model of critical thinking and public health
action.

24. THANK YOU