Public health surveillance is defined as the systematic collection, analysis, interpretation, and dissemination of health-related data that guides health interventions. It serves as an early warning system for epidemics, informing about disease patterns, monitoring trends, and evaluating public health programs. Various types include passive, active, and sentinel surveillance, each fulfilling specific functions in disease detection and monitoring.

1. Epidemiologic Surveillance
Dambi Dollo University

2. Definition of Surveillance
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o Surveillance is derived from the French ‘Sur’ (over)
and ‘veiller’ (to watch) - hence ‘to watch over’.
Public Health Surveillance is an on-going
 systematic collection,
 analysis,
 interpretation and
 Dissemination of health-related data essential to the
planning, implementation, and evaluation of public
health practice.

3. Cont…
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 Surveillance can be conducted globally, regionally (like
East Africa), nationally, or institutionally (single health
facility-focused).
 It is a mechanism that public health agencies use to
monitor the health of the community.
 It is for evidence-based setting priorities, planning
programs, and taking action to promote and protect the
public’s health.

4. Basic Principle
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 Public health surveillance’s main function is to serve as
an “early warning system” – providing timely
information needed for action
 (rapid reporting, confirmation, decision making and
response)

5. Surveillance System’s Good Attributes
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 Simple
 Flexible
 Acceptable
 Sensitive; able to detect the problem
 Good predictive value positive; good yield
 Representative
 Timely
 Cost effective

6. Uses of Public Health Surveillance
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 To estimate magnitude of the problem
 Early recognition of epidemics - detect sudden changes in
disease occurrence.
 To identify changes in agents, host factors and health practices
 To follow secular (long-term) trends
 Projections of future trends
 To evaluate public health programs
 To generate hypotheses and stimulate research

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Surveillance is
Information for Action
Surveillance
Collection
Analysis
Interpretation
Dissemination
Public Health Action
Assess PH status
Detect outbreaks/epidemics
Monitor trends in endemic
diseases
Define PH priorities
Guide research
Monitor and evaluate
programs/interventions
Predict outbreaks/epidemics
Estimate future disease impact

8. Sources of Surveillance Data
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 Census data
 Mortality reports (along with
birth and death certificates)
 Morbidity reports
 Hospital data
 Absenteeism records (school,
workplace)
 Epidemic reports
 Laboratory reports and records
 Drug utilization records
 Adverse drug reaction reports
 Special surveys (research data,
serologic surveys)
 Police records (injury, alcohol-
related)
 Information on animal reservoirs
and vectors
 Environmental data (water, food
testing)
 Special surveillance data (injury,
occupational H.)

9. Selection Criteria for Disease Surveillance
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 Magnitude of the disease
 Feasibility of control measures
 Need for monitoring and evaluating the
performance of a control program
 Resource availability

10. Types of Surveillance
There are 3 main types of surveillance:
1. Passive Surveillance: A surveillance where reports are
awaited and no attempts are made to seek reports actively
from the participants in the system.
2. Active Surveillance: A surveillance where public health
officers seek reports from participants in the surveillance
system on a regular basis, rather than waiting for the
reports.
10
10/09/2024

11. Types (Cont…)
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3. Sentinel Surveillance: uses a pre-arranged sample of
reporting sources to report all cases of one or more
conditions.
 Usually the sample sources are selected to be those most
likely to see cases.
 Sentinel surveillance provides a practical alternative to
population-based surveillance.

12. Main Purposes of Sentinel Surveillance
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 To detect changes
 To direct and focus control efforts
 To develop intervention strategies
 To promote further investigations
 Provide the basis for evaluating preventive strategies and
activities

13. Types (Cont…)
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Modified forms of surveillance include:
1. Intensified Surveillance: The upgrading from a passive to
an active surveillance system for a specified reason and for a
limited period (could be because of an outbreak).
2. Enhanced Surveillance: The collection of additional data
about cases reported under routine surveillance

14. Critical Information in Surveillance
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 Generally, a surveillance system should determine the Who,
What, When, Where, and How questions. The critical
information should include:
 Person: Age, sex
 Time: onset of disease, reporting period
 Place: Woreda, region
 Risk factors
 Number of cases (magnitude)
 Treatment outcome: deaths, recovery (seriousness)
 Mode of treatment: inpatient/outpatient

15. Case Definition
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 Case definition includes:
 Criteria: Signs and symptoms with or without a
laboratory test
 Restriction by time, place and person can be done
depending on the nature of the disease
 There are 3 classification of case definitions:
confirmed, probable, and possible cases.

16. Case Definition (Cont…)
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Classification of case definitions:
1. Confirmed: a case definition by appropriate
laboratory test.
2. Probable: a case with typical clinical features of the
disease without laboratory confirmation
3. Possible/Suspect: a case with few of the typical clinical
features.
Use case definition consistently!!

17. Case Definition: Example
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Confirmed
Malaria Case
Probable
Malaria Case
Possible/
Suspected
Malaria
Confirmed by
laboratory test.
Presence of fever,
chills, headache,
arthralgia, back
pain…etc of
sudden onset, but
without laboratory
confirmation.
Presence of fever
and headache of
sudden onset
without
laboratory
confirmation.

18. Major Advantages of Case Definition
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Facilitates early detection and prompt management
of cases.
Useful in areas where there is no laboratory.
Facilitates observation of trends.
Facilitates comparison more accurately from area
to area.

19. Surveillance System With Laboratory Tests
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Clear procedures need to be designed and
established for effective surveillance system
that address:
 Specimen and Data collection
 Transfer of Specimen and data
 Feedback

20. Quality of Public Health Surveillance System
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The major indicators of quality public health surveillance
system include:
I. Acceptability
II. Representativeness
III. Reporting completeness
IV. Reporting timeliness
V. Sensitivity of surveillance
VI. Specificity of surveillance

21. I. Acceptability
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 Willingness of persons conducting surveillance
and those providing data to generate accurate,
consistent and timely data.

22. II. Representativeness
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 The degree to which inference can be drawn
from the information gathered by the
surveillance system to the target population.

23. III. Reporting Completeness
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 Proportion of all expected reports in a reporting
system that were actually received.

24. IV. Reporting Timeliness
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 Proportion of all expected reports in a reporting
system received by a given date (due date).

25. V. Sensitivity of Surveillance
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 The ability of a surveillance or reporting system to
detect true health events:
total number of health events detected by the system
total number of true health events
(as determined by an independent and more) complete
means of ascertainment

26. VI. Specificity of Surveillance
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A measure of how infrequently a system
detects false positive health events:

27. Analysis of Surveillance Data
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 Descriptive analysis: distribution by time, place and person
 Frequency of events
 Calculate rates- need proper denominator
 Observe trends: comparison current data with expected
value, identify differences, and assess the relevance of the
difference
 Draw graphs to show long term (secular) trends

28. Analysis Cont…
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29. Dissemination of Surveillance Data
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 Disseminate surveillance data to all stakeholders
 Those who provide the reports (health providers)
 The community – affected/potentially affected
 Decision makers
 Disseminate report locally, nationally or globally; as
deemed necessary
 Disseminate report timely and regularly
 Disseminate through appropriate media: newsletter or
bulletin (paper or electronic)

30. 10/09/2024
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Federal MOH
 Central Referral
Hospitals
Regional Health Bureau
 Regional hospitals
 Regional laboratories
Zonal Health Department
 District Hospital
 PHC facilities
Woreda Health Office
 District hospital
 PHC facilities
The
community
WHO
Data Collection, Analysis,
Action and Reporting
Supervision and feedback
.

31. Reporting and Feedback Levels
(Local to International)
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 Surveillance systems are networks of people and
activities that maintain the process and may function at
a range of levels, from local to international.

32. Evaluating and Improving Surveillance Systems
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Should be evaluated periodically to forward
recommendations for improvement:
1. To identify elements of surveillance that should be
enhanced to improve its attributes,
2. To assesses how surveillance findings affect control
efforts, and
3. To improve the quality of data and interpretations
provided by surveillance.

33. Common Limitations of Surveillance Systems
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 Under reporting
 Lack of representativeness of reported cases
 Lack of timeliness
 Inconsistency of case-definitions
 Lack and shortage of qualified staff
 Lack of motivation

34. Surveillance Vs survey
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Surveillance
 Relatively cheap - can often
use existing systems and
health personnel
 Allows monitoring of trends
of disease over time
 Ongoing collection
produces enough cases for
the study
But…
 Quality control may be the
major problem
 May not provide
representative data
Survey
 More in-depth data could be
collected
 More accurate assessment of
true prevalence
 Can identify those which do
not warrant medical care
But…
 Costly
 Represents only a single point
in time- does not show changes
over time
 Recall bias can be introduced
(retrospective data)

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Public Health Surveillance in
Ethiopia

36. Background of Disease Surveillance in Ethiopia
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 Before 1998 Multiple D/s Surveillances
→
 From 1998 – 2009 → Integrated Disease Surveillance and
Response (IDSR)
 Starting from early 2009 Public Health Emergency
→
Management (PHEM)

37. Public Health Emergency Management (PHEM)
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 PHEM is the process of
 anticipating,
 preventing,
 preparing for,
 detecting,
 responding to,
 controlling and
 recovering from consequences of public health threats
so that health and economic impacts are minimized.

38. IDSR and PHEM
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 IDSR and PHEM employ simplified tools for data
collection and analysis & common channels for reporting
and feedback.
 IDSR & PHEM strengthened the capacity to detect and
respond to communicable disease threats and emergencies.
 The integration helped to maximize effective utilization of
scarce resources.

39. List of Priority Diseases for Surveillance in Ethiopia
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 Nationally, 23 disease were monitored until early
2009.
• From early 2009, twenty (20 but currently 22 ) diseases
and conditions are identified as priority diseases on
surveillance which are immediately and weekly
reportable.
 Other diseases are included in HMIS

40. Immediately Reportable Diseases
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1. Acute Flaccid Paralysis (AFP) /Polio
2. Anthrax
3. Avian Human Influenza (H1N1)
4. Cholera
5. Dracunculiasis / Guinea worm
6. Measles
7. NNT (Neonatal Tetanus)
8. Pandemic Influenza A
9. Rabies
10. Smallpox
11. SARS (Severe Acute Respiratory
Syndrome)
12. VHF (Viral Hemorrhagic Fever)
13. Yellow fever

41. Weekly Reportable Diseases
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Immediately Reportable Diseases Plus
14. Dysentery
15. Malaria
16. Meningococcal Meningitis
17. Relapsing fever
18. Malnutrition
19. Typhoid fever
20. Typhus + all IRD

42. Exercise/Assignment
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 According to current PHEM concerns, determine whether IRD or
WRD ????????
1. MDSR
2. AEFI
3. MERS (Middle East Respiratory
4. GBS (Gullian Bare Syndrome) and
5. Microcephally of ZickaVirus
 What about these??????????????????
 Flooding, Earth quake, Volcanic Eruption, landslide

43. Outbreak Investigation & Control
Dambi Dollo University

44. Learning objectives
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After the end of this session, students will be able to:
o State different level of disease occurrences
o List the rationale to investigate outbreak occurrence
o Discuss steps in the investigation of an outbreak
occurrence
o Describe types of outbreak occurrence
o Discuss the outbreak controlling strategies

45. Epidemiology in Action
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 Outbreak Investigations
 Public Health Surveillance
 Community Screening Programs

46. 10/09/2024
Levels of Disease Occurrence
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 Diseases occur in a community at different levels at a
particular time in time:
1. Expected Level (Predictable) and
2. Excess of expected
 Expected level of occurrence of disease
 Endemic: the usual presence of disease from low to moderate level
==Malaria is endemic in the lowland areas of Ethiopia.
 Hypo/Meso/Hyper-endemic: a persistently lower or
moderate or high level of disease.
 Sporadic: Normally does not occur, but occasional cases
occur at irregular intervals

47. Excess of what is expected
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 Epidemic: The occurrence of health related condition/disease
in excess of the usual frequency
 Outbreak: Epidemics of shorter duration covering a more
limited area.
 Pandemic: An epidemic involving several countries or
continents affecting a large number of people.
example : HIV/AIDS,Covid-19 are pandemic.

48. 10/09/2024
Levels of Disease Occurrence
48
.
(Endemic Vs Epidemic)
Epidemic
Endemic
Time
Number
of
Cases
of
a
Disease
Hyperendemic

49. 10/09/2024
Levels of Disease
49
.
Increasing amount of disease
Pandemic
Epidemic
Endemic
Sporadic

50. What does outbreak investigation & control?
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It is the process of identifying:
o The cause of the epidemic
o The source of the epidemic
o The mode of transmission and
o Taking preventive and control measures

51. Source of an outbreak information
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 Routine surveillance
 Health professionals
 Affected community members

52. What are the objectives for outbreak investigation?
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1) To initiate control & prevention measures
 The most important public health reasons for
investigating an outbreak are to help guide disease
prevention and control strategies.
 These disease control efforts depend on several factors,
Including
 knowledge of the agent,
 The natural course of the outbreak,
 The usual transmission mechanism of the disease, and
 Available control measures

53. 2) Research and training opportunity
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o Each outbreak should be viewed as an experiment
waiting to be analyzed
o It presents a unique opportunity to study the natural
history of the disease
o It could be a good opportunity to gain additional
knowledge on
 The impact of prevention and control measures
 The usefulness of new epidemiology and laboratory
techniques

54. 3) Public, political and legal obligations
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o Politicians and leaders are usually concerned with control of
the epidemic
o Politicians and leaders may sometimes override scientific
concerns
o The public are more concerned in cluster of disease and
potentials of getting medication
o It is right of the community to get treatment/service and it is
government and our duty to protect the community

55. 4) Program considerations
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o Occurrence of an outbreak notifies the presence of a
program weakness
o This could help program directors to change or
strengthen the program’s effort in the future to prevent
potential episodes of outbreak occurrence

56. Steps of outbreak investigation and control
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1. Prepare to field work
2. Establish the existence of outbreak
3. Verifying the diagnosis
4. Case definition and case finding
5. Perform descriptive epidemiology
6. Formulate hypotheses
7. Testing hypotheses
8. Refine hypothesis and additional studies
9. Implementing prevention and control activities
10. Communicate findings
 In practice, however, several steps may be done at the same time, or
 The circumstances of the outbreak may dictate that a different order
be followed

57. Step 1: Prepare for field work
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 Before leaving for the field, an investigator must be well
prepared to under take the investigation:
 Investigation (Knowledge in epidemiology and the disease of
concern is important)
 Administrative (Logistics, administrative procedures, travel
arrangements)
 Consultation (Health workers should know their role, and should
participate in the planning phase)

58. Step 2: Establish the existence of outbreak
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 An outbreak is the occurrence of more cases of disease than
expected level
 The investigator has to compare previous case load with the
current to assure the existence of the outbreak
 But be careful, excess cases may not always indicate an
outbreak occurrence rather it may be because:
 Change in population size
 Change in case definition
 Change in reporting procedure

59. Step 3: Verifying the diagnosis
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 The initial report may be spurious and arise from
misinterpretation of the clinical features
 Review clinical and laboratory findings to establish
diagnosis
 Goals in verifying the diagnosis includes:
 To ensure that the problem has been properly diagnosed
 To rule out laboratory error as a basis for the increase in
diagnosed cases
 To ensure the diagnosed disease is possibly epidemic

60. Step 4: Case definition and case finding
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 Prepare “case definition” before starting identification of cases
 It’s aim is to count all cases of the illness
 It is clinical criteria restricted by time, place and person
 Use sensitive or "loose case definition” early in the investigation and use
"tight or strict case definition” for testing hypothesis
= We can find additional cases in
- health facilities
- home visit in epidemic area( kebele or gote level )
=Information required include personal Identifier(name, tell, address),
demographic(age, sex, occupation), exposure history, clinical information(date of
onset, outcome, sign and symptom),who report? Information
= we will do line listing by taking the above information

61. 10/09/2024
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62. 10/09/2024
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Classification of Case Definition
 Possible: cases with subjective signs and symptoms
consistent with the case definition.
 Probable: cases with objective signs and symptoms
consistent with the case definition.
 Definite: laboratory confirmed case

63. Step 5: Performing Descriptive Epidemiology
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 Once data is collected, it should be analyzed by time,
place and person
 The tools to be used when characterizing the epidemic
are epidemic curve, spot map and attack rate
 The characterization often provides clues about
etiology, source and modes of transmission that can be
turned into testable epidemiologic hypothesis

64. 1. Analysis of epidemic by time
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 We use epidemic curve to analyze by time taking
- The X- axis; indicating time of onset
-The y-axis; indicating the number of cases appearing
 Epidemic curve can tell as
- nature of epidemic
- hint to etiologies – etiologic agent
- hint about source of exposure
 There are three principal types of epidemic
1. Common source – based on source of exposure
2. Propagative - touches mode of transmission
3. Mixed epidemic – share characteristics of both type

65. 1. Common source epidemic
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 It occurs as a result of the exposure of a group of population to a
common source (etiological agent)
o It can result from a single source/ exposure of the
population to the agent
E.g: contaminated water supply, or food in a certain
restaurant
 Three types
1. Point common source
2. Continuous common source
3. Intermittent common source

66. A) Point common source epidemic
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 Single/ones/limited time exposure to the source
 All exposed hosts will develop disease within one
incubation period
 The epidemic usually decline after a few generations,
either because the number of susceptible hosts fall
below some critical level, or because intervention
measures become effective
 A rapid rise and gradual fall of an epidemic curve
suggests a point source epidemic

67. Typical Point source epidemics
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Minimum
incubation
period
Peak of Outbreak
A single sharp peak of sudden onset

68. B) Continuous common source epidemic
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 If exposure to a common source continues over time for days,
weeks
 The epidemic curve has a plateau (multimodal epi curve)/ long
peak
 Range of exposures and range of incubation periods is different

69. C) Intermittent common source epidemic
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 Results in an irregular pattern of the epidemic curve that reflects
the intermittent nature of the exposure
E.g. waterborne outbreak
 Often the graph is atypical
Several sharp peaks

70. 2. Propagative /progressive epidemic
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 It occurs as a result of transmission of an infectious agent from
one person to another directly or indirectly
 There is a successive generations of cases
 The epidemic curve in a progressive epidemic is usually presence
of successive several peaks, a prolonged duration, and usually a
sharp fall
 Can show geographic spread of the case
 Example; Malaria outbreak and different vector born disease

71. Typical Propagated Epidemic Curve
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No sharp peak

72. 3. Mixed Epidemic
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 It shows the features of both types of epidemics
 It begins with a common source of infectious agent
with subsequent propagated spread because of person
– to- person transmission of the etiologic agent
 E.g. Majority of food borne outbreaks

73. 10/09/2024
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74. 2. Analysis of epidemic by place
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 A spot map is a simple and useful technique for
illustrating where cases live, work or may have been
exposed
 Area map if large area is affected
 It is important to indicate source of outbreak

75. 3. Analysis of epidemic by person
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 Characterizing an outbreak occurrence by person is how we
determine what populations are at risk for the disease
 Host characteristics: age, race, sex, or medical status and
exposures-occupation, leisure activities, use of medications,
tobacco and drug use etc…
 These influence susceptibility to disease and opportunities for
exposure to risk factors
 We use attack rates to identify high risk groups

76. Step 6: Formulating hypothesis
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 Depending on the outbreak, the hypothesis may address
 The exposures that caused the disease
 The mode of transmission
 Using :
 Subject-matter knowledge
 Descriptive epidemiology
 Talking with patients
 Talking with local officials
 The hypotheses should be testable

77. Step 7: Testing the hypothesis
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 Here doing analytic studies may be useful.
 Association between the postulated exposure factor and the disease
is tested using analytic design
1. Case control 2. Retrospective Cohort
 Appropriate measure of association should be made
 for case control, odds ratio
 for cohort design, relative risk
 Significance of statistics should be done,
 (Chi-square is the appropriate test, and P-value is estimated at 5 %.)

78. Step 8: Refining hypotheses and additional studies
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o Search for additional cases: Locate unrecognised or
unreported cases
o Environmental studies are equally important in some
settings

79. Step 9: Implementing control and prevention
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In outbreak investigation, the primary goal is to control and
prevent the outbreak.
Implementing control measure should be done as soon as
possible
It should go in parallel to investigating the outbreak
Source/ Mode ofTransmission
Causative
Agent

80. Control measures (do early)
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1. Measures Directed Against the Reservoir:
 Reduce contact rate
 Reduce infectious sources- destruction of infected animal /isolation
 Reduce infectiousness- early treatment
2. Measures that interrupt the transmission of organisms
 Purification of water
 Pasteurization of milk
 Inspection procedures designed to ensure safe food supply.
 Improve housing conditions
3. Measures that reduce host susceptibility and Increase herd
immunity
- Immunization
- Chemoprophylaxis - Use of antibiotics for known contacts of cases

81. Step 10: Communicating findings of investigation
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 The final responsibility of the investigative team is to prepare
a written report to document the investigations, findings and
the recommendations
 The written report should follow the scientific reporting format
which includes:
o Introduction
o Methods
o Results
o Discussion
o Conclusion, and
o Recommendations

82. Summary of the investigation and control of an epidemic considering procedure
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.

83. Post-Epidemic Surveillance
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 The efficacy of control measures should be assessed day by day
during the outbreak, a final assessment being made after it has
ended
 this will provide a logical basis for post-epidemic surveillance,
and preventive measures aimed at avoiding similar outbreaks in
the future
 develop long term early warning system
 monitor environmental risk factors

84. The end
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Any questions or comments??