The document defines key terms related to epidemics such as epidemic, endemic, outbreak, sporadic, and pandemic. It discusses the iceberg concept of infectious disease and explains that only a small portion of cases are clinically apparent. The levels of response to different disease triggers are outlined. The document also covers the objectives and steps of an epidemic investigation including developing a case definition, confirming the existence of an epidemic, defining the population at risk, rapidly searching for cases, analyzing data through epidemiological curves, and formulating and testing hypotheses. Control measures and the importance of forecasting and preventing future epidemics are also summarized.

1. SHABNA.G.S
FIRST YEAR MDS
GOVERNMENT DENTAL COLLEGE
KOTTAYAM
1

2. CONTENTS
1. DEFINITIONS
2. LEVEL OF RESPONSE TO DIFFERENT TRIGGERS.
3. THE ICEBERG CONCEPT OF INFECTIOUS DISEASE.
4. TYPES OF EPIDEMICS
5. MANAGEMENT OF EPIDEMICS
6. STAGES OR EPIDEMIC MANAGEMENT
7. FORECASTING OF AN EPIDEMIC
8. EPIDEMIC INVESTIGATION
9. STEPS IN EPIDEMIC INVESTIGATION
10. CONTROL MEASURES FOR AN OUTBREAK
11. PREVENTIVE MEASURES OF AN EPIDEMIC
12. CONCLUSIONS
13. REFERENCES
2

3. COMPETENCY TO BE GAINED
FROM THIS LECTURE
3

4. DEFINITIONS
1.EPIDEMIC : The “ unusual ” occurrence in a community
or region of the disease, specific health related behavior or
other health related events clearly in excess of “ expected
occurrence ”. Emergencies caused by epidemics remain
one of the most important challenges to National health
administration.[Park Textbook of Preventive and Social Medicine :K
Park 22th ed.M/s Bhanot Jabalpur India.2013 pg no-122-127]
4

5. OCCURRENCE OF AN
EPIDEMIC
5
Host
Environment Agent
An outbreak comes from a change
in the way the host, the environment
and the agent interact.
[Park's Textbook of Preventive and
Social Medicine]

6. 6
3.ENDEMIC : The constant presence of a disease or
infectious agent within a given geographical area or
population group, without importation from outside. e.g.
HepatitisA, cholera
2.OUTBREAK: It is used for a small, usually localized
epidemic.

7. Endemic
Epidemic
ENDEMIC VS.
EPIDEMIC
7
TIME
NUMBEROFCASES

8. 8
4.SPORADIC: The word sporadic means scattered about, cases
occurs irregularly, haphazardly & infrequently from time to time.
e.g.,polio, tetanus, herpes zoster.
5.PANDEMIC: An epidemic usually affecting a large proportion of
the population, occurring over a wide geographic area. e.g.,
HIV/AIDS, Influenza. [Park's Textbook of Preventive and
Social Medicine]

9. 9

10. LEVEL OF RESPONSE TO DIFFERENT
TRIGGERS [SOURCE;IDSP training module for state and district
surveillance officers -Case definitions of diseases and syndromes under
surveillance]
10
Trigger 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
Natural disaster
• Local,district,State and
centre
5 Pandemic • International

11. 11
DISEASE TRIGGER 1 TRIGGER 2
MALARIA •Single case of smear positive in an area
where malaria was not present for a minimum
of three months.
•Slide positivity rate doubling over last three
months.
•Single death from clinically/microscopically
proven malaria.
•Single falciparum case of indigenous origin
in a free region.
•Two fold rise in
malaria in the
region over last 3
months.
•More than 5
cases of
falciparum of
indigenous origin.
POLIO •Even a single case will trigger outbreak
investigations.
PLAGUE •At least 1
probable case of
plague in
community.
JAUNDICE More than 2 cases of jaundice in different
houses irrespective of age in a village or 1000
population.

12. WHAT IS AN EPIDEMIC?
A public health emergency!
A political emergency!
An economic emergency!
An event requiring rapid action!
Surveillance failure!
Control failure!
An opportunity!
12

13. THE ICEBERG CONCEPT OF
INFECTIOUS DISEASE
13

14.  The floating tip- what the physician sees in the
community,i.e.,clinical cases.
The vast submerged portion of the iceberg- the
hidden mass of disease.
The waterline represents the demarcation between
apparent and inapparent disease.
[Park's Textbook of Preventive and Social
Medicine]
14

15. Outbreak Detection and Response
With Preparedness
15

16. Outbreak Detection and Response
Without Preparedness
[WHO Outbreak Investigation and Response Manual]
16

17. TYPES OF EPIDEMICS
[Park's Textbook of Preventive and Social Medicine]
Common source epidemics
1.Single exposure or point source epidemics
2.Continuous or multiple exposure epidemics
Propagated epidemics
1.Person to person
2.Arthropod vector
3.Animal reservoir
Slow epidemics 17

18. 18
Common source outbreaks –
-all came into contact with the same unsafe source of infection
(the common source), such as contaminated food or water.

19. Common source outbreak
19

20. 20
A point source outbreak is a common source outbreak
where the exposure period (e.g. the time at which the
contaminated food was eaten) is short.
In continuous or multiple exposure epidemics,the
exposure from the same source may be prolonged-
continuous,repeated or intermittent-not necessarily at the
same time or place.

21. Propagated source epidemics
21

22. 22
Propagated or progressive epidemics occur when the
infection spreads from person to person.
DIRECT SPREAD
INDIRECT SPREAD

23. 23
COMPARE COMMON
SOURCE
PROPAGATED
SOURCE
1.Curve Bell curve Scatter bell
2.Transmission One source From person to
person
3.Duration Short Long
4. Control Eradicate source Health education

24. 24
Mixed epidemics show characteristics of both common
source and propagated epidemics. So a mixed epidemic can
start with a common source and be followed by a
propagated spread. Mixed epidemics are often caused by
food borne infectious agents.

25. MANAGEMENT OF
EPIDEMICS
25
“Management of an epidemic
involve step by step activities
starting from forecasting to
prevention for future
occurrence.”

26. STAGES OR EPIDEMIC
MANAGEMENT
26
1. Forecasting of Epidemic.
2. Investigation of Epidemic.
3. Control of Epidemic.
4. Prevention of Epidemic

27. 27

28. FORECASTING OF AN
EPIDEMIC
28
•Forecasting is an early warning system.
• May not totally prevent the epidemic , but definitely control
its severity and spread to other areas.

29. METHODS OF
FORECASTING
29
For forecasting the epidemic the prerequisite are –
 Study of incidence and prevalence rate.
 Disease specific morbidity and mortality rate.
 Age and Sex wise morbidity and mortality rates.

30. 30
•The various data are tabulated month wise and year wise for
the last three years (3 years) for comparison study of the
pattern of disease.
• Then the collected data is plotted on graph for immediate
detection and visual appreciation through analysis of the
disease.

31. EPIDEMIC
INVESTIGATION
An epidemic investigation calls for inference as well as
description.
•Frequently, epidemic investigations are called for after
the peak of the epidemic has occurred;
•In such cases, the investigation is mainly retrospective.
[Park's Textbook of Preventive and Social Medicine]
31

32. Why investigate an outbreak ?
Public Health rationale
– To reduce or prevent mortality
– To reduce morbidity
– To design control and preventive measures
Delayed or improper interventions = DEATHS
32

33. OBJECTIVES OF AN
EPIDEMIC INVESTIGATION
The objectives of an epidemic investigation are-
a.To define the magnitude of the epidemic outbreak or
involvement in terms of time, place and person.
b.To determine particular conditions and factors
responsible for the occurrence of the epidemic.
c.To identify the causative agent, sources of infection,
and modes of transmission.
•d.To make recommendations to prevent recurrence.
[Park's Textbook of Preventive and Social Medicine]
33

34. 34

35. INFORMATION OF OUTBREAK:
35
DOCTORS NURSES
LABORATORY PERSONNELS

36. 36
Official disease notification system/or surveillance system
Newspaper or media
Village health volunteers
Calls from a Citizen

37. DETERMINANTS OF
OUTBREAK
37
Herd Immunity:
Herd immunity is a form of immunity that occurs when the
vaccination of a significant portion of a population (or herd)
provides a measure of protection for individuals who have
not developed immunity.’

38. 38

39. 39
Incubation Period: Interval from receipt of infection
to the time of onset of clinical illness.
 Important in case of isolating infected people to prevent
transmission.
 Isolation or quarantine should be greater than maximum
incubation period.
 Useful if disease may be introduced into new areas

40. 40
Quarantine: The restriction of activities of well persons or
animals who have been exposed to a case of communicable
disease during its period of communicability (i.e. contacts) to
prevent disease transmission during incubation period if
infection should occur.

41. INVESTIGATIVE TEAM
INCLUDES
41
Investigator
Field epidemiologist
Disease control people e.g sanitary inspector
Laboratory technicians
Specialist in particular areas e.g veterinarian would be
very helpful in outbreak of zoonotic disease
Public health administration for providing logistic support,
mobilizing resources and providing administrative
support.

42. 42
Public relation person :In certain conditions when the
outbreak has caused panic or gained the intense attention of
public, the investigative team should recruit or appoint a
person to be in charge of public relations and press releases.
This person should appropriately reassure and not unduly
alarm the public

43. STEPS IN AN EPIDEMIC
INVESTIGATION
1.Verification of diagnosis
2. Confirmation of the existence of an epidemic
3. Defining the population at risk
4. Rapid search for all cases and their characteristics
5. Data analysis
6. Formulation of hypothesis
7. Testing of hypothesis
8. Evaluation of ecological factors
9. Further investigation of population at risk
10. Writing the report
43

44. 44

45. DISEASES REQUIRING
INVESTIGATION
45
1.Endemic diseases with a potential of causing focal or
large outbreaks.
2.Diseases under eradication or elimination phase.
3.Rare but internationally important diseases.
4.Outbreaks of unknown diseases or syndromes.

46. VERIFICATION OF
DIAGNOSIS•First step in the investigation.
•The report may be spurious due to misinterpretation of
signs or symptoms by the lay public .
• It is not necessary to examine all the cases.
•A clinical examination of a sample of cases is sufficient.
• Laboratory investigations are most useful to confirm the
diagnosis.
46

47. Develop case definition, start case
finding, and collect information on
cases
47
Define cases ( Establish case definition):
 Case definition should be broad enough to include most, if
not all, of the actual cases.(sensitive not specific)
 Case definition must not include an exposure or risk factor
you want to test
 Case definition must be equally applied and without bias
to all persons under the investigation

48. 48
Usually includes four components:
 clinical information about the disease,
 characteristics about the people who are affected,
 information about the location or place, and a specification
of time during which the outbreak occurred

49. 49
Confirmed cases– have a positive laboratory result
(isolation of the causative agent or positive serological test).
e.g outbreak of bloody diarrhoea E.coli 0157:H7 is
isolaated from a stool culture.

50. 50
Probable cases – have the typical clinical features of the
illness but without laboratory confirmation.
e.g bloody diarrhoea or hemolytic uremia syndrome
without microbiological confirmation
Possible case: have fewer or atypical clinical features.
e.g. non-bloody diarrhoea without microbiological
confirmation

51. CONFIRMATION OF THE
EXISTENCE OF AN EPIDEMIC
•Done by comparing the disease frequencies during the
same period of previous years.
•An epidemic is said to exist when the number of
cases(observed frequency)is in excess of the expected
frequency for that population ,based on past experience.
51

52. •In case of yellow fever, bubonic plague and polio even a
single case will constitute an epidemic in India.
• But in the US single case of cholera constitute epidemic.
The criteria are:
• A 25% increase in the number of cases reported as
compared to corresponding period of previous year.
• A 25% increase in the number of cases reported as
compared to the average number of cases over last four
non-epidemic years for the corresponding period. 52

53. DEFINING THE POPULATION
AT RISK
Obtaining the map of the area
It should contain information about natural landmarks, roads
and location of all dwelling units along each road.
 The area may be divided into segments, using natural
landmarks as boundaries.
This is again divided into smaller sections. Within each
section, the dwelling units may be designated by numbers.
Counting the population
By doing census by house to house visits. The composition
should be known by age and sex.
Eg: For population at risk; In case of food poisoning-
those who ate the food. In case of outbreak of cholera-
those who were using water from the suspected well.
53

54. 54
John Snow (1813–1858)
An English physician and modern-day father of
epidemiology.
He used scientific methods to identify the cause of the
epidemic of cholera in London in 1854.
He believed that it was the water pump on Broad Street
that was responsible for the disease.The removal of the
pump handle ended the outbreak.
[SOURCE;Mode of Communication of Cholera. By John Snow, MD: Second
Edition – London, 1855, pp 162. EA Parkes International Journal of
Epidemiology, Volume 42, Issue 6]

55. SOHO, LONDON, 1854
Large urban population, densely populated, widespread
poverty. No sewage or sanitation system.
On 31 August 1854, a major outbreak of cholera struck
Soho.
– "the most terrible outbreak of cholera which ever
occurred in the kingdom."
Over the next three days ,127 people on or near Broad
Street died.In the next week, three quarters of the
residents had fled the area.By 10 September, 500 people
had died and the mortality rate was12.8 percent in some
parts of the city.
55

56. "A COURT FOR KING
CHOLERA”
[SOURCE;"http://www.victorianweb.org/science/health/cholera/thomas.htl]
56

57. JOHN SNOW’S MAP OF
CHOLERA CASES
[SOURCE-https://www1.udel.edu/johnmack/frec682/cholera/]
57

58. "CHOLERA IN BROAD
STREET, SOHO"
58
[SOURCE;"http://www.victorianweb.org/science/health/cho
lera/thomas.htl]

59. SOHO, LONDON
59

60. RAPID SEARCH OF ALL THE
CASES AND THEIR
CHARACTERISTICSMedical survey
Epidemiological case sheet
This should be carefully designed to collect relevant
information.
 If the epidemic is large it may not be possible to examine
all the cases. In such cases random sample should be
examined.
60

61. Searching for more cases
The patient is asked about the similar cases at home, family,
neighborhood, school, work place having an onset within the
incubation period of index case.
 The search for new cases should be carried out everyday
till the area is declared free of epidemic.
61

62. DATA ANALYSIS
It has to be done using the parameters – Time, Place
And Person.
a. Time
Prepare a chronological distribution of dates of onset of
cases and construct an “epidemic curve”. An epidemic
curve suggests :
 Pattern of spread
Magnitude
Outliers
 Exposure and/or disease incubation period
62

63. EPIDEMIC CURVE
•An epidemic curve, or “epi curve,” is a visual display of
the onset of illness among cases associated with an
outbreak.
•The horizontal x-axis is the date or time of illness onset
among cases.
•The vertical y-axis is the number of cases.
•Each axis is divided into equally spaced intervals,
although the intervals for the two axes may differ.
63

64. EPIDEMIC CURVE
64
[Centers for Disease Control and
Prevention publication]

65. WHAT AN EPI CURVE CAN
TELL YOU
•Time trend of the outbreak, that is, the distribution of cases
over time
•“Outliers,” or cases that stand apart from the overall pattern
•The outbreak's magnitude
•The outbreak's pattern of spread
•Time of exposure
65

66. •The magnitude of an outbreak can be assessed easily
with a glance of the epi curve.
 Are there many cases or just a few?
•The time trend, or the distribution of cases over time, will
give an indication of where the outbreak is in its course.
 Are cases still rising or has the outbreak already peaked?
Does it appear that the outbreak is over?
How long has it been since the last case occurred?
66

67. MAGNITUDE, TIME TREND, AND
OUTLIERS
Below is the epi curve from an outbreak of hepatitis A. If
today's date is August 17
The incubation period for hepatitis A is 25-30 days.
67

68. Magnitude
Based on currently reported cases, the outbreak involves 17 total cases.
Hepatitis A cases by date of onset in Port Yourtown, Washington, June -
August 2010
68

69. Time Trend
The first case of hepatitis A occurred during the third week of
June, almost 3 weeks before the other cases. The majority of
cases began the week of July 14 and peaked the week of July
21. The last case onset of symptoms appeared during the week
of August 10.
Hepatitis A Cases by Date of Onset in Port Yourtown,
Washington, June - August 2010
69

70. Outliers
The first case arouses suspicion because it occurs about one
incubation period before the other cases. This could be the source
of the outbreak.
Hepatitis A Cases by Date of Onset in Port Yourtown,
Washington, June – August 2010
70

71. Mode of Spread: Point Source
Transmission occurs in the following ways:
•Point source
•Continuous common source
•Person-to-person spread (propagation)
In a point source outbreak-
• The number of cases rises rapidly to a peak and falls gradually.
• one incubation period of the disease.
71

72. MODE OF SPREAD: POINT SOURCE
72

73. Mode of Spread: Continuous Common Source
In a continuous common source outbreak, persons are exposed
to the same source but exposure is prolonged over a period of
days, weeks, or longer. The epi curve rises gradually and might
plateau.
73

74. Mode of Spread: Propagated Outbreak
In a propagated outbreak, there is no common source because
the outbreak spreads from person-to-person. The graph will
assume the classic epi curve shape of progressively taller peaks,
each being one incubation period apart.
Measles Cases by Date of Onset in Aberdeen, South Dakota,
October 15, 1970 – January 16, 1971
74

75. Place
 Prepare a ‘spot map’ of cases and if possible their relation
to the sources of infection e.g. water supply, air pollution,
foods eaten, occupation etc..
75

76. 76

77. 77
Analyze the data by age, sex, occupation and other possible
risk factors.
Determine the attack rates/case fatality rates.
The purpose of data analysis is
1. To determine modes of transmission and the source and the
vehicle of the agent, so that the most effective measures can
be initiated.
2. To determine the risk factors for disease.
Person

78. 78

79. FORMULATION OF HYPOTHESES
Hypothesis is a proposition or a tentative theory
designed to explain the observed distribution of the
disease in terms of causal association of the direct
nature.
The hypothesis should explain the epidemic in terms of
1. Causative agent
2. The possible source
3. Possible modes of spread
4. The environmental factors which enabled it to occur. 79

80. TESTING OF
HYPOTHESES
80
TWO APPROACHES:
1.Comparison of the hypotheses with the established facts
-when the evidence is so strong that the hypothesis does not
need to be tested.
2.Analytical epidemiology - which allows to test hypothesis,
when the cause is less clear.
case control study
cohort study

81. Study Design Comparison
81
Cohort Case-Control
Illness occurs within a well-
defined population
Illness does not occur in a
well-defined population
Compares rates of illness
among those with risk factor
and those without risk factor
Compares exposures
among people with illness
and those without illness
Relative risk (RR) Odds ratio (OR)

82. EVALUATION OF
ECOLOGICAL FACTORS
 The ecological factors which have made the epidemic
possible should be investigated such as sanitary status of
eating establishments, breakdown in the water supply
system, changes such as temperature, humidity, and air
pollution, population dynamics of insects and animal
reservoirs etc..
82

83. FURTHER INVESTIGATION
OF POPULATION AT RISK
Needed to obtain further information.
 This may involve medical examination, screening tests,
examination of suspected food, feces or food samples,
biochemical studies, assessment of immunity status etc.
83

84. WRITING THE
REPORTBackground
 Climatic conditions
 Demographic status (population pyramid)
 Socioeconomic situation
 Organization of health services
 Surveillance and early warning systems
 Geographical location
 Normal disease prevalence
84

85. Historical data
Previous occurrence of epidemics
- of the same disease
- locally or elsewhere
 Occurrence of similar diseases
- in the same area
- in other areas
 Discovery of the first cases of the present outbreak
Investigations
85

86. Analysis of data
Clinical data
- frequency of signs and symptoms
- course of disease
- differential diagnosis
- death rates
 Epidemiological data
- Mode of occurrence
- In time
- By place
- By population groups A
86

87. Modes of transmission
Laboratory data
- isolation of agents
- serological confirmation
- significance of results
 Interpretation of data
- comprehensive picture of the outbreak
- hypothesis
- formulation and testing of hypothesis 87

88. Control measures
Evaluation
- significance of results
- cost/effectiveness
Preventive measures
88

89. 89

90. 90

91. RECENT EPIDEMICS IN 21ST
CENTURY
91
YEAR DISEASE
2002–2003 SARS[ASIA]
2007 EBOLA[CONGO]
2009 GUJARAT HEPATITIS
OUTBREAK[INDIA]
2012 MIDDLE EAST RESPIRATORY
SYNDROME (MERS)
2014 EBOLA[WEST AFRICA] ,
JAPANESE ENCEPHALITIS[INDIA],
ODISHA JAUNDICE
OUTBREAK[INDIA]
2015 ZIKA VIRUS EPIDEMIC

92. 92
YEAR DISEASE
2015 INDIAN SWINE FLU
OUTBREAK[INDIA]
2017 GORAKHPUR JAPANESE
ENCEPHALITIS
OUTBREAK[INDIA]
2018 NIPAH VIRUS OUTBREAK[INDIA]

93. Matrix for the communication of the
findings of an outbreak investigation
to various audiences
93
AUDIENCE MEDIUM FOCUS OF THE
CONTENT
COMMUNICATION
OBJECTIVE
Epidemiologists,
laboratory
Report Epidemiology Documentation of
the source
Public health
managers
Summary Recommendations Action
Political leaders Briefing Control measures Evidence that the
situation is under
control
Community Press release,
interview
Health education Personal steps
towards prevention
Scientific
community
Presentation,
manuscript
Science Scientific progress

94. COMMON INTERVENTIONS
USED TO CONTROL AN
EPIDEMIC
94
REMOVAL OF SOURCE OF INFECTION
• Treatment of infected cases.
• Destruction of reservoir of infection.
[Maxcy-rosenau public health and preventive medicine 15th edition]

95. 95
PREVENTION OF TRANSMISSION
• Isolation of infected cases.
• Hand washing and personal protective measures.
• Improve environmental sanitation.
• Contact tracing .(family , neighbor).
• Screening of suspected cases.
• Health education.
• Increase resistance of suspects throug Immunization
and prophylactic drugs

96. 96
VECTOR CONTROL MEASURES
• Prevention of breeding of mosquitoes
• Destruction of adult vector through insecticide, pesticide.
• Personal protection like use of mosquito net,
• use hot food and filtered water.
• Increase personal hygiene.
• Improve environmental sanitation.

97. PREVENTIVE MEASURES
OF AN EPIDEMIC
97
•There is saying that “more you sweat during the peace,
less you bleed during the war.”
• Appropriate measures at right time, right place ,in right
quantity can prevent the severity of any epidemic.

98. 98
PREVENTIVE MEASURES
1.Improvement of the hygienic level of population.
2. Vaccination.
3. Prophylactic disinfection.
4. Health education.
5. Environmental Measures.
- Lighted and well ventilated houses.
- Clean potable water supply.
- Proper disposal of waste.
- Adequate sewerage system.

99. CONCLUSION
99
It may be necessary to implement temporary control
measures at the commencement of an epidemic on the
basis of known facts of the disease.
These measures may be modified or replaced in the light of
new knowledge acquired by the epidemic investigation.

100. 100
Epidemiologic investigations are essential to determine
source of outbreaks.
• Be systematic
• Follow the steps!

101. 101
REFERENCE
Maxcy-rosenau public health and preventive medicine 15th edition
Park's Textbook of Preventive and Social Medicine-24TH EDITION
WHO Outbreak Investigation and Response Manual
IDSP training module for state and district surveillance officers -Case
definitions of diseases and syndromes under surveillance

102. 102
THANK U