outbreak epidemic endemic pandemic seasonal variation infectious disease

1. DISEASE OUTBREAK
DEPARTMENT OF EPIDEMIOLOGY AND BIOSTATISTICS
2011
1

2.  OUTBREAK
 EPIDEMIC
 ENDEMIC
 PANDEMIC
 SEASONAL VARIATION
 CHANCE
2

3. EPIDEMIC/OUTBREAK
The occurrence of cases of an illness,
specific health-related behavior,
or other health-related events,
in a community or region,
clearly in excess of normal expectations.
The community or region and the period
in which the cases occur are specified precisely.
3

4. EPIDEMIC
• The number of cases indicating the presence
of an epidemic varies according to the agent,
size and type of population exposed,
previous experience or lack of exposure to the
disease, and time and place of occurrence.
4

5. ENDEMIC
The constant presence of a disease
or infectious agent within a given geographic
area or population group; may also refer to
the usual prevalence of a given disease within
such area or group
5

6. PANDEMIC
• Worldwide epidemic
SEASONAL VARIATION
• Change in physiological status
or in disease occurrence that conforms to a
regular seasonal pattern
6

7. CHANCE
• A set of cases that occur in a short period of time,
BUT
do not surpass the expected number of cases for
the region
7

8. Infectious Disease
(Communicable Disease)
An illness due to specific infectious agent
or its toxic product that arises through transmission
that agent or its products from an infectious person,
animal or reservoir to a susceptible host.
8

9. Factors Involved in Infection
Agent, host and environment interrelate
and are interdependent in the production of disease
Agent
Environment Host
9

10. Types of Transmission
Direct transmission (person to person)
 Direct projection of droplet spray
(sneezes and coughs : measles)
 Vertical transmission
(transplacental, from mother to child : HIV)
 Mucosa to mucosa
(sexually transmitted disease)
 Blood and transplants
(hepatitis)
 Skin to skin
(staphylococcus) 10

11. Types of Transmission
Indirect transmission
 Vehicle-borne transmission
(water, food, milk, biological products,
contaminated materials or objects)
 Vector-borne transmission
(mechanical, biological)
 Airborne transmission
(microbial aerosols)
11

12. Infectious Chain Model
Mode of transmission
Portal of exit
Portal of entry
Reservoir
Susceptible host
Agent
12

13. Other Definitions
Vehicle
Mode of transport of an infectious agent
through the environment to a susceptible host.
Vector
A living carrier (usually an arthropod) that serves as
a mode of transport for an infectious agent from an
infected host to a susceptible host.
Reservoir
The primary habitat in which an infectious agent
survives and reproduces.
13

14. Carrier
A person or animal that harbors a specific infectious agent
in the absence of discernable clinical disease
and serves as a potential source of infection.
 Asymptomatic carrier
Subclinical infection throughout the infectious carrier state
 Incubationary carrier
Infectious carrier state occurs during the incubation period
preceding clinically recognizable disease
 Convalescent carrier
Infectious carrier state continues during convalescence
when clinically recognizable disease is no longer present 14

15. Periods
Exposure period
Time during which an individual or group
is exposed to a source of infection
Incubation period
Time from initial infection (entry of infection)
to onset of clinical illness.
(Usually expressed as the median or sometimes
the arithmetic or geometric mean, minimum and
maximum incubation period)
15

16. Periods
Infectious (or communicable) period
Period during which an infected person is able
to transmit the infectious agent.
(Important to know this for various agents
in order to impose appropriate control measures).
16

17. Periods
Latent period
Time from receiving infection to onset of
infectiousness.
Minimum interval between successive
infections in a chain of transmission.
17

18. Periods
Serial interval or generation time
Interval between the same stage of illness
in sucessive cases in a chain of transmission.
(Only applicable when infection spreads from
person to person e.g. the interval between
onset of rash in the primary case to onset of
rash in a secondary case)
18

19. Use of Periods
Useful for several reasons :
 Quarantine
 Contact tracing
 Identification of possible time of infection
 Outbreak investigation
 Disease modeling and forecasting
19

20. Types of Outbreak
1. Common source
Transmission of an infectious agent involving a source
that is common to all outbreak-associated cases
 Point source : brief common exposure.
A single source of pathogen results in exposure of persons
at one point in time
 Extended source :
Common source exposure present over days or weeks
- intermitten : at several points in time
- continuous : over a continuous period
Onset will still be abrupt but cases would be spread
over a greater period of time than one incubation period
depending upon how long the exposure persists. 20

21. Types of Outbreak
2. Propagated or progressive (person to person)
- Caused by the spread of the pathogen
from one susceptible person to another.
- The curve tend to have a series of irregular peaks
reflecting the number of generations of infection.
3. Mixed epidemic
Involves both a common source epidemic and
secondary propagated spread to other individuals.
Many foodborne pathogens commonly exhibit this
mode of spread (hepatitis A, Shigella, E.coli). 21

22. Elements of Control
 Removal or elimination of the source of the
pathogen
 Blockage of the transmission process
 Elimination of susceptibility
(e.g. vaccination)
22

23. DISEASE OUTBREAK INVESTIGATION
Data sources
 The public
 The media
 Reports of clinical cases from health care providers
 Surveillance data
(laboratory reports, disease notifications)
23

24. When reports of an outbreak are received,
the following information should be gathered :
 The person(s) reporting the outbreak
 Characteristics of the suspected outbreak
(clinical information, suspected etiologies)
 Persons directly affected by the outbreak
(epidemiological information)
24

25. Steps in outbreak investigation
 Establishing the existence of an outbreak
 Verifying the diagnosis
 Defining and counting cases
 Determining the population at risk
 Describing the epidemiology
 Developing hypotheses
 Evaluating the hypotheses
 Undertaking additional epidemiological,
environmental and laboratory studies, as necessary
 Implementing control and prevention measures
 Communicating findings
25

26. CONFIRMATION & VERIFICATION OF DIAGNOSIS
 Check the report whether it is true or not
(see the case by yourself in the field)
 Verify the sign or symptoms and the diagnosis
 To proof the case is based on the history of the disease
and the sign or symptoms
 Estimate the number of cases
 If there is sufficient of time, a laboratory examination
should be done to make an etiological diagnosis
26

27. DETERMINE THE EVENT :
IS IT AN EPIDEMIC OR NOT?
 How much the usual morbidity rate are?
 Based on time, place, person
 How are the usual pattern of the disease in the community?
 Is the disease usually presence or never?
 Is there an increase of the number of cases?
 Is it conspicuous or not?
 Make a graph of epidemic curve based on time of onset
of the sign in each case! 27

28. DESCRIBE THE EPIDEMIC :
IN TIME, PLACE AND PERSON
TIME
• When was the first case founded? The last?
• How long the epidemic/outbreak happened?
• Find the probable of the first exposed time!
• Assume the type of the epidemic!
(common source ? person to person?)
28

29. PLACE
• What place is the most prominent number of cases?
• What are the attack rate based on places?
PERSON
• Identify the age specific and sex specific attack rate!
• What group has the highest and the lowest attack rate?
• Determine that the characteristic of the cases are differ
significantly compared with the whole population
29

30. COLLECTING DATA
 To get the real data.
 Can be simultaneously with the activity of diagnosis
verification :
- What are the exact number of cases ?
- Who are the population at risk ?
- Who are the contact person ?
- Think about loss of observation !
- Who are the carrier ?
 Those data could be obtained by house to house visits ! 30

31. IDENTIFICATION OF AGENT OR THE SOURCE
OF INFECTION AND TRANSMISSION
First we have to set hypothesis of :
• The etiological agent
• The source of infection
• The exposure time
• The incubation period
• The transmission of infection
• The population at risk
31

32. EPIDEMIC CONTROL (MANAGEMENT)
1. THE PATIENT
Adequate and prompt treatment
2. CONTROLLING against :
• the primary source of infection
• the reservoir (carrier, vector, environment)
• Transmission vehicle (food, fluid, air etc.)
• Susceptible contact person
3. EPIDEMIOLOGICAL SURVEILLANCE
32

33. INVESTIGATION REPORT
The main objection of the report is to describe
the experience and all findings in the occurrence
of epidemic, to organize and operate a surveillance
activity and to improve the previous prevention
and controlling activity.
33

34. INVESTIGATION REPORT
The form of the report are :
1. INTRODUCTION
It content description of the condition that stimulate
to carry out an investigation.
2. BACKGROUND
A brief description about factors that cause the problem
(e.g. geographic, politic, economic, demographic
and historic)
34

35. 3. DESCRIPTION OF INVESTIGATION ARRANGEMENT
Include :
- the reason
- the method
- source of information
- how to explore the cases
- verification of diagnoses
- use of sample cases and control in analyzing data, etc.
35

36. 4. THE FINDINGS
• Only the fact finding should be reported;
without any comment, discussion or suggestion.
The recent data could be related to the previous data
as it happened as an epidemic.
• The findings will be presented in tables or graph such as :
- characteristic table of age, sex, race, occupation etc.
and their attack rate
- the onset of illness with the graph
- the result of laboratory test
- other evidence which might direct the possibility
of the source of infection or suspected source.
36

37. ANALYZING DATA AND CONCLUSION
Data should be interpreted to construct hypothesis of :
- agent of infection
- source of infection
- reservoir
- disease transmission, including the vehicle or vector
- the high risk group population
It is exactly useful if the characteristic of the recent
epidemic compared with the similar epidemic before.
37

38. DESCRIBE THE CONTROL ACTION
Clarify the objective of the action specifically.
Discuss each of this action based on :
How, When, Where and by Whom.
Describe the results and the expenses of the
actions.
Explain that there might be possibility of explosion
of new cases after passing one incubation period
after the control action.
38

39. DESCRIBE THE OUTCOMES
a. The consequences of the epidemic to health
condition and economic status
b. The consequences of the control action to :
Population → immunity status, way of life, etc.
Reservoir → number and distribution
Vector → number,density, distribution
c. The invention of new infectious agent, reservoir,
transmission of agent etc.
39

40. RECOMMENDATION
The objection is to improve the surveillance activity and
control.
These report can be useful as reference
in surveillance activity, what data should be collected,
what is the source of data, how to consolidate
after an epidemic, dissemination of the report,
who will be responsible in an epidemic, what kind of
cooperation should be organized.
40

41. EPIDEMIC CURVE
A graph of cases of disease plotted against
time (date or hour) of onset of illness.
Mainly used in outbreak investigation.
41

42. EPIDEMIC CURVE
STEPS OF MAKING DIAGRAM
1. Draw the X and Y line : X for time of onset of cases
Y for the number of cases
2. Select interval of time depend on the incubation period
of the disease, e.g. hourly, daily, weekly or monthly
To estimate the first contact or exposed to source of the disease :
1. Take a line from the first case(s) backward at length of 14 days
(the minimum I.P.) and from the last case(s) at length of 21 days
(maximum I.P.). The results are fallen at the 7th and 8th days;
it means that the first contact to the source of disease was at the
7th and 8th days.
2. It can also can be done by subtraction the last and the first time
of onset by the maximum and the minimum incubation period
42

43. 21 days
(max incubation period)
14 days
(minimum incubation period)
Probable period
of exposure
43

44. EPIDEMIC CURVE
0
1
2
3
4
5
6
7
8
9
10
0
1
/
0
1
/
1
9
0
0
0
3
/
0
1
/
1
9
0
0
0
5
/
0
1
/
1
9
0
0
0
7
/
0
1
/
1
9
0
0
0
9
/
0
1
/
1
9
0
0
1
1
/
0
1
/
1
9
0
0
1
3
/
0
1
/
1
9
0
0
1
5
/
0
1
/
1
9
0
0
1
7
/
0
1
/
1
9
0
0
1
9
/
0
1
/
1
9
0
0
2
1
/
0
1
/
1
9
0
0
2
3
/
0
1
/
1
9
0
0
2
5
/
0
1
/
1
9
0
0
2
7
/
0
1
/
1
9
0
0
2
9
/
0
1
/
1
9
0
0
Date of Onset of Illness
Number
of
Cases
Point source epidemic
44

45. CHICKENPOX OUTBREAK IN A ROSEAU
PREPARATORY SCHOOOL
0
1
2
3
4
5
6
7
8
9
10
11
12
27-Dec-01
03-Jan-02
10-Jan-02
17-Jan-02
24-Jan-02
31-Jan-02
07-Feb-02
14-Feb-02
21-Feb-02
28-Feb-02
07-Mar-02
14-Mar-02
DATE OF ONSET
NUMBER
OF
CASES
Propagated outbreak
45

46. Cases of Salmonellosis by Date of Onset
0
5
10
15
20
25
30
4a
4p
5a
5p
6a
6p
7a
7p
8a
8p
9a
9p
10a
10p
11a
11p
12a
12p
13a
13p
14a
14p
15a
15p
Onset by 12 hour intervals
Number
of
cases
Extended source epidemic
46

47. ATTACK RATE
Similar as incidence rate :
It is used in a short period of an event - an outbreak -,
the population being affected is limited closely,
the duration of epidemic is short period.
 new events / cases
Incidence Rate = x k
Population at risk
47

48. Outbreak Control Team (OCT)
The criteria for convening a multidisciplinary OCT
will vary according to the seriousness of the illness,
its geographical spread, local circumstances
and the available resources.
48

49. An OCT may be considered when :
 The outbreak poses an immediate health hazard to the
local population
 There are many cases
 The disease is important in terms of its severity or its
propensity to spread
 Cases have occured over a widespread area without
obvious point source
 Cases have occured in high-risk establishments
(schools, day-care centres, hospitals, food premises,etc.)
49

50. The role of the OCT :
to coordinate all the activities involved
in the investigation and control of an outbreak.
This may involve :
1. Deciding whether there is really an outbreak
2. Deciding on the type of investigations to be conducted
3. Case-finding and interviews
4. Planning the appropriate clinical and environmental
sampling
50

51. 5. Ensuring that all collaborators use a complementary
methodology
6. Conducting an environmental investigation
of suspected source
7. Agreeing and implementing control measures
to prevent the further spread
8. Working in concert with local medical providers
to make recommendations on treatment and/or
prophylaxis
51

52. 9.Organizing ongoing communications among
OCT members about the outbreak
10.Making arrangements for liaison with the media
11.Producing reports, including lessons learned,
for health authorities and other interested parties
12.Requesting external assistance
(e.g. secondment of a national investigation team)
52

53. Coordinating role of the OCT in an
outbreak investigation
clinicians epidemiology laboratory environment
OCT
authorities public
reports control measures media
53

54. Definitions in an outbreak investigation
CLINICAL DESCRIPTION
Sign and symptoms found in the outbreak
CASE DEFINITION
• Standard set of criteria for deciding whether an individual
should be classified as having the health condition
of interest.
• A case definition includes clinical criteria and particularly
in the setting of an outbreak investigation restrictions by
time, place, and person.
54

55. Case definition
Confirmed cases :
- have a positive laboratory result
- high spesificity
Probable cases :
have the typical clinical features of the illness,
but without laboratory confirmation
Possible cases :
- have fewer or atypical clinical features
- high sensitivity
55

56. DIFFERENTIAL DIAGNOSIS
List of possible diagnosis, ordered from the most
possible one
DESCRIPTIVE EPIDEMIOLOGY
Characterize the outbreak by time, place and
person
56

57. Place
A. The occurrence of diarrhea by source of water supply of
community A and B in January 2011
Source of water
supply
Sick Not Sick total Attack Rate
Community A 98 57 155 63.2 %
Community B :
Not exposed by water
supply A
Visit A :
1. Drank water of A
2. Not drank water of A
9
22
0
132
18
6
141
40
6
6.4 %
55,0 %
0
Total Community B 31 156 187 16.6 %
The attack rate of B was much lower than the attack rate of A.
In other case, people of B who visited A and drank the water A became sick,
the attack rate was 55.0% ;a quite high incidence.
Conclusion : water supply A was responsible for the occurrence of diarrhea. 57

58. Rank of Class No. of Cases No. of student Attack Rate in %
Test Class
1
2
3
4
5
6
Special Class
24
17
7
8
4
23
12
5
85
86
61
90
104
99
95
12
28.2
19.8
11.5
8.9
3.8
23.2
12.6
41.7
Total 100 632 15.8
The table shows that the highest risk is the special class out of the whole
population, followed by the test class, the 5th and the first class.
The lowest is the 4th class.
B. Attack rate by class in Ganado Public School, Arizona in March 2011
58

59. C. The occurrence of hepatitis A among restaurant worker
who work at night at May 12 and 13, 2011
Work
nightly
Sick Not sick Total Attack
rate
Yes 10 12 22 45 %
No 2 26 28 7 %
Total 12 38 50 24 %
The table shows that the night workers are much higher risk to get
hepatitis than non night worker.
59

60. PERSON
Attack rate per 100 person by age group in diarrhea
in Polyclinic A.
Group of 1 & 2 years are the highest risk of getting diarrhea,
followed by group of 3 years.
Age group
in year
Examined
regularly
Diarrheal
Cases
Attack Rate
(%)
1
2
3
4
5
6+
20
19
39
39
38
18
17
15
13
4
5
1
85
79
33
10
13
6
Total 173 55 32
60

61. 61