epidemiologic imvestigation and management

1. 1
Epidemic Investigation
&
Management
By: Firdawek G.

2. Objectives 2
At the end of this session, you should able to :
 Define terms like disease outbreak , epidemic,…
 Describe the purpose of epidemic investigation
 Differentiate types of epidemic
 Describe steps in the investigation of epidemic

3. Content 3
 Definition of terms
 Purpose of epidemic investigation
 Types of epidemic
 Steps in the investigation of epidemic

4. 4
How do you define the following terms:
1. Endemic disease
2. Hyper-endemic disease
3. Epidemic disease
4. Disease outbreak
5. Pandemic disease
6. Cluster of cases

5. Definition of terms
5
Endemic disease
Presence of a disease at more or less stable/
constant level within a particular place
 This level is not necessarily the desired level, which
may in fact be zero, but rather is the observed level
Hyper-endemic disease
 Persistent, high levels of disease occurrence
Sporadic disease
A disease that occurs occasionally & has no certain
pattern(occur infrequently and irregularly)

6. Definition of terms …
6
Epidemic disease
 occurrence of more cases of disease than
expected(above endemic level) in a given area or
among a specific group of people over a particular
time
Usually, the cases are presumed to have a common
cause or to be related to one another in some way
Disease Outbreak
 epidemics of shorter duration covering a more
limited area

7. Definition of terms …
7
Cluster of cases
aggregation of cases in a given area over a
particular period without regard to whether the
number of cases is more than expected
Pandemic disease
an epidemic that has spread over several countries
or continents, affecting a large number of people

8.  To control /stop the spread of disease
 To know magnitude of the problem
 To identify who is at risk
 To assess the causes of disease, its source &
mode of transmission
 To prevent future epidemic
Purpose of outbreak investigation
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9. Types of epidemics
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 Epidemics (outbreaks) can be classified according to the
method of spread and length of exposure to the agent
A. Common Source Epidemic
 Disease occurs as a result of exposure of a group of
susceptible persons to a common source of a pathogen,
often at the same time or within a brief time period

10. 10
 When the exposure is simultaneous, the resulting
cases develop within one incubation period and this
is called a point source epidemic.
 The epidemic curve in a point source epidemic will
commonly show a sharp rise and fall
E.g Food borne epidemic following an event where the
food was served to many people

11. point source epidemic
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12. 12
 If the exposure to a common source continues over time,
it will result in a continuous common source epidemic.
E.g A waterborne outbreak that is spread through a
contaminated community water supply
 The epidemic curve may have a wide peak because of
the range of exposures and the range of incubation
periods.

13. continuous common source epidemic
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14. 14
B. Propagative / Progressive Epidemics.
 infectious agent is transferred from one host to another
 It can last longer than common source
 In propagated outbreaks, cases occur over more than
one incubation period.
 Propagative spread usually results in an epidemic curve
with a relatively gentle upslope and somewhat
steeper tail (series of progressively taller peaks)

15. 15
E.g outbreak of malaria.
 In the propagated epidemics there will be successive
generations of cases.
 The epidemic usually wanes after a few generations,b/c
 the number of susceptible persons falls below some
critical level required to sustain transmission, or
 the intervention measures become effective.

16. propagated epidemics
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17. 17
C. Mixed Epidemics
 Have features of both common-source epidemics and
propagated epidemics
 The epidemic begins with a single, common source of an
infectious agent with subsequent propagative spread.
 Many food borne pathogens result in mixed epidemics.

18. Steps of an epidemic Investigation
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1. Prepare for fieldwork
2. Establish existence of an epidemic
3. Verify the diagnosis
4. Define & identify cases
5. Analyze data by person, place, and time
6. Develop hypotheses
7. Evaluate hypotheses (analytical studies)
8. Reconsider/refine hypotheses (additional studies)
9. Implement control and prevention measures
10. Communicate findings

19. 1. Prepare for Field Work
Decide to investigate the suspected outbreak if:
1. A report of a suspected epidemic of an immediately
notifiyable disease is received
2. Unusual increase is seen in the number of deaths during
routine analysis of data
3. Alert or action thresholds have been reached
4. Communities report rumors of deaths or large cases
5. A cluster of deaths occurs for which the cause is not
explained or is unusual
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20. Example of Outbreak thresholds
S. No Name of disease Threshold level
1 AFP Single confirmed cases
2 Anthrax Single confirmed cases
3 Avian Human Influenza Single confirmed cases
4 Cholera Single confirmed cases
5
Dracunculiasis/Guinea
worm Single confirmed cases
6 Measles 5 suspected or 3 confirmed cases
7 NNT Single suspected case
8 Pandemic Influenza A Single confirmed case
9 Rabies Single suspected/confirmed case
10 SARS Single confirmed case
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21. 1. Prepare for Field Work...
Assemble the team members
An epidemiologist/public health expert
A clinician
A laboratory professional
Environmental health expert
More professional depending of the type of
events/diseases
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22. 1. Prepare for Field Work…
Identify the roles and responsibilities among:
 Team Members
 Different sectors & partners
Discuss Scientific knowledge
 with someone knowledgeable and using available
references such as journal articles, guidelines, about the
disease:
 Source, Root of transmission, Risk factors,…
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23. 1. Prepare for Field Work…
Avail relevant resources
 Different formats(Case based,line list,…)
 Relevant guidelines
 Personal protective equipment (PPE)
 Laptop and wireless network
 Mobile phone with communication cost if
necessary
 Transportation
 Personal matters
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24. 2. Establish existence of an Epidemic
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25. 2. Establish the Existence of an Outbreak…
To establish existence of an outbreak:
 See trends in cases and deaths due to the disease
over the last 1-5 years
 Know the epidemic threshold for that particular
disease
 Compare the reported case versus the baseline
(Local/national source, neighboring areas)
 Check real versus artifact
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26. 2. Establish the Existence of an Outbreak…
 The increase in the number of cases might be:
 True increase in incidence
 Change in reporting procedures
 Change in case definition
 Improvements in diagnostic procedures
 Increased awareness
 Increased access to health care
 Laboratory or diagnostic error
 Double reporting
 Change in denominator
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27. 3.Verify/confirm the Diagnosis
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 First, review the clinical findings and laboratory
results
 Ask a qualified laboratory professional to review
the laboratory techniques being used
 Collect and send laboratory specimen to
specialized laboratory

28. 3.Verify the Diagnosis…
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 Second, talk with some case patients
 Better understanding of clinical pictures
 Useful to generate hypothesis about the disease
etiology and spread
 Third, summarize the clinical features using
frequency distribution
Used to develop the case definition

29. 4. Define & identify cases
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A case is an event that happens:
To a person
 In a given place
At a given time
 Establish a case definition using:
 Clinical picture :Sign,Symptom,Lab.result and
 Epidemiological parameter: Time ,Person ,
Place

30. 4. Define & identify cases…
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 Conduct surveillance using case definition
 Search for additional cases
1. Search for additional suspected cases and deaths in
the registers.
2. Look for other patients by identifying areas where:
the patients have lived,
The patient worked,
The patient travelled
3. Search in neighboring health facilities
4. Collect data using line list

31. 4. Define & identify cases…
 Talk to other informants in the community:
 Health extension workers,
 Pharmacists,
 Health workers,
 School teachers,
 Veterinarians,
 Farmers and community leaders etc.
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32. 4. Define & identify cases…
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Line listing
 rectangular database similar to spreadsheet
 Provides summary of key data about cases
 Each row represents one case
 Each column represents one variable
 Can be paper or electronic
 Can be quickly reviewed and updated

33. 33
Signs/Symptoms
Lab. Demogra
phics
Ca
se
no
.
Name Date of
Symptom
Onset
Place Diarrhe
a Vomiting
Fever Positive
stool
culture
Age Sex
1 Abebe 12/05/13 A Y Y Not
done
Not
submitt
ed
16 M
2 Kebede 13/05/13 A Y Y Y Y 18 M
3 Ayele 14/05/13 B Y N Y Y 23 M
4 Biruk 15/05/13 B N N Y N 32 F
5 Bayu 16/05/13 B Y Y N N 29 F
6 Dagim 17/05/13 B N Y Y Y 28 F

34. 5.Analyze data by person, place, time
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Time
Ideally, when were they infected?
 More practically, when did they become ill?
Is the trend of the disease increasing/ decreasing
/maintaining over time
The overall shape of the epidemic curve can reveal
the type of outbreak

35. 5.Analyze data by person, place, time
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Place (spot map, shaded map)
 Ideally, where were they infected?
 More commonly, where do they live, work?
 Describe the geographic extent of the problem.
 Identify and describe any clusters or patterns of
transmission or exposure.
 Depending on the organism that has contributed to this
epidemic, specify the proximity of the cases to likely
sources of infection.

36. 5.Analyze data by person, place, time
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Person (tables)
Who was infected ?age,sex,occupation,…
 Numerators and denominators
What do the cases have in common?

37. 6.Develop hypotheses
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 The hypothesis should address:
The source of the agent
The exposures that caused the disease, etc.
Why and how the outbreak occurred
Talk to case-patients –what do they think?
Talk with health officials ,What do they think?
Recommended to generate more than one hypothesis

38.  Use already available evidence about the suspected disease
 the agent’s usual reservoir/source
 usual mode of transmission
 Known risk factors
 Review descriptive epidemiology(ppt)
 When was the event highest
 Which areas have the highest attack rates
 What groups are at greatest risk
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39. 7.Evaluate hypotheses (analytical studies)
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If evidence of the cause is less clear/not strong, test
your hypothesis
Apply:
 cohort study & risk ratio
 case-control study & odds ratio
 Otherwise, compare facts with hypotheses

40. 8. Refine hypotheses and carry out
additional studies
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 Conduct additional studies
 Environmental studies: food,water,living
environment,…
 Laboratory based study
 If analytic study results are conclusive, don’t wait for
positive samples before implementing prevention

41. 9.Implement control and prevention measures
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 Implement as early as possible
“The perfect is the enemy of the good ” meaning, roughly right
and timely is better than precisely right and late
 An outbreak may be controlled by:
 Eliminating or reducing the source of infection
 Interrupting transmission and
 Protecting persons at risk.
 Create mechanism to evaluate effectiveness mgt measures

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 Work with regulators, industry, and health educators
to institute control measures
 Create mechanism to evaluate both short and long-
term success of control / prevention measures

43. What should be the priority action in an epidemic?
Causative agent Source/ mode of transmission
Known Unknown
Known Investigation +
Control +++
Investigation +++
Control +
Unknown Investigation +++
Control +++
Investigation +++
Control +
+++ = highest priority
+ = Lower priority

44. Measures Directed Against the Reservoir
Domestic animals as reservoir •Immunization
•Testing of herds
•Destruction of infected animals
Wild animals as reservoir •Post-exposure prophylaxis
Humans as reservoir •Removal of the focus of infection
•Isolation of infected persons.
•Treatment to make them noninfectious.
•Disinfection of contaminated objects.
•Quarantine

45. Measures that interrupt the transmission of organisms
For diseases transmitted by
ingestion
•Purification of water
•Pasteurization of milk
•Inspection procedures designed to
ensure safe food supply
•Improve housing conditions
For diseases transmitted by
respiratory routes
•Chemical disinfection of air and use of
ultraviolet light
•Work on ventilation patterns, like
unidirectional (“laminar”) air flow to reduce
the transmission of organisms in hospitals.
For diseases whose cycles
involve an intermediate host
•Clearing irrigation farms from snails to
control schistosomiasis

46. Measures that reduce host susceptibility
Active immunization •Mass vaccination
•Selective vaccination
Passive immunization •Transfer of maternal antibodies to the
fetus through the placenta
•Prophylaxis administration of immune
serum globulin(ISG)
Chemoprophylaxis •Use of antibiotics for known contacts of
cases
•Use of prophylaxis to persons traveling to
endemic areas.

47. 10.Communicate Findings
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 No report means little contribution of improving
scientific and public health knowledge
To whom we communicate?
 Communicate to Decision Makers
 Communicate to Health Workers
 Communicate to the Public and Media

48. 10.Communicate Findings
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Communicate through:
Oral briefing for local health authorities
Written report
 The report should hold the following scientific format:
Introduction, Methods, Results, Discussion ,
Conclusion and Recommendations.

49. Thank you!
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