2. Goals
The goals of this presentation are to:
Provide a general overview of the basic steps of disease outbreak
investigations
Describe factors that may contribute to a decision to investigate
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
2
3. Outbreak
A sudden increase in the number of individuals who contact a specific infectious disease in a population,
putting others at risk.
OR
Spread of disease, which occurs in a short period of time and in a limited geographic location (i.e,
neighborhood, community, school, or hospital)
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
3
4. Why investigate an outbreak?
Characterize a public health problem
Identify preventable risk factors
Provide new research insights into disease
Train health department staff in methods of public health
investigations and emergency response
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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5. When to Investigate
5
• Consider the following
factors:
– Severity of illness
– Transmissibility
– Unanswered questions
– Ongoing illness / exposure
– Public concern
– Prevention potential
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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6. Outbreak Investigations
Three critical variables in investigating an outbreak or epidemic are:
When did the exposure take place?
When did the disease begin?
What was the incubation period for the disease?
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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7. In the Beginning…
Successful investigations require a multidisciplinary approach, effective communication
and collaboration
Steps:
Assemble team members
Present available information
Outline plan for investigation and team communication
Assign roles and responsibilities
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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8. Prepare for Field Work
8
• Identification of team
• Gather resources, supplies, equipment
– Computer, questionnaires, specimen collection kits
• Make necessary administrative, personal arrangements
for travel
– Determine role in the investigation
– Identify points of contact (field and office)
• What do you need to do to prepare?
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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9. Team Member Roles
Team Leader
Experience in outbreak investigation and epidemiology
Selection can be result of outbreak setting or etiologic agent
Role can be filled by:
County health director,
Public health nurse,
Epidemiologist, or
Environmental health specialist
Role may change depending on stage of investigation
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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10. Team Member Roles
Epidemiologist
Develop study design and survey
questionnaires
Create database and conduct data analysis
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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11. Team Member Roles
Microbiologist
Verify the diagnosis
Subtype pathogens to help refine case
definition
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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12. Team Member Roles
Environmental health specialists (EHS)
Collect food and environmental samples
Provide guidance on food safety regulations and
engineering
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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13. Team Member Roles
Interviewers
Collect data in person or by telephone
Role can be filled by health department personnel, state
or federal personnel, or health science students
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
13
14. Team Member Roles
Clinicians
Administer vaccines or prophylaxis
Collect clinical specimens
Role can be filled by health department or local
medical community
May include veterinarians, depending on type of
outbreak 03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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15. Team Member Roles
Regulators
Facilitate identification of the source of outbreak and develop prevention
strategies
Role can be filled by state or federal agency employees
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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16. Team Member Roles
Media Spokesperson
Deliver clear and consistent messages to community
Role can be filled by one outbreak team member or representatives from each
agency
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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17. Questions to Consider
What resources, including personnel, are available?
What resources could be provided by outside collaborators?
Who will direct the day-to-day investigation?
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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18. More Questions to Consider
Who will interact with the media?
How will data be shared and analyzed?
Who will write the final report and present the
information?
How will the team communicate with each other?
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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19. Team Equipment
Computer with access to internet
Email communication
Literature searches (PUBMED)
Data entry and analysis (Epi-Info 2002 http://www.cdc.gov/epiinfo/epiinfo.htm)
Written reports
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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20. Team Equipment
Specimen collection tools
Rectal swabs or specimen cups
Phlebotomy equipment
Cooler to transport specimens
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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21. Communication
Information flows in both directions
Leader should update the team during meetings, conference calls, or email
Members provide regular updates to team leader
Acts as tool for measuring progress
Enables leader to provide feedback and direction to team members
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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22. Communication
Keep lines of communication open through regular meetings or phone
Include local, state, and federal public health agencies
Document progress
Allows all members to remain up-to-date
Assists in drafting final report
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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23. Steps of an Outbreak
Investigation
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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24. Steps of an Outbreak Investigation
1. Preparation
2. Confirm the existence of outbreak
3. Verify the diagnosis
4. Establish a case definition
5. Find cases systematically & record information
6. Perform descriptive epidemiology
7. Develop hypotheses
8. Evaluate hypotheses epidemiologically
9. As necessary, reconsider, refine, and re-evaluate hypotheses.
10.Implement control and prevention measures
11. Communicate findings
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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25. 1. Preparation
Investigation
Scientific knowledge
Review literature
Consult experts
Sample questionnaires
Supplies
Consult with laboratory
Equipment
Laptop, camera etc.
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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26. 2. Establish existence of an outbreak
Is an outbreak truly occurred?
through surveillance records for notifiable diseases.
hospital data.
data from other facilities
community survey.
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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27. 2. Establish Existence of an Outbreak
27
• For non-notifiable conditions:
– National estimates
– Hospital discharge records
– Mortality data
– Other available records
– Use data from neighboring areas
– Call local health care providers
– Call community members
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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28. Example: Establish Existence of an Outbreak
An Outbreak...To Be or Not To Be
100
80
60
40
20
0
Time
28
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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29. Example: Establish Existence of an
Outbreak
An Outbreak...To Be or Not To Be
100
80
60
40
20
0
Time
29
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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30. 3. Verify the Diagnosis
Ensure proper diagnosis and rule out lab error as the bias for increased diagnosis
Review clinical findings, lab results
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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31. Verify the Diagnosis
cont.
See and talk with patients if at all possible
Better understand clinical features
Gather critical information
Source of exposure
What they think caused illness
Knowledge of others with similar illness
Helpful in generating ideas for hypothesis about etiology and spread
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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32. 4. Establish a case definition
Case definition
Includes clinical criteria and restrictions by time, place and person
Classification
Definite (confirmed)
Laboratory confirmed
Probable
Typical clinical features without lab confirmation
Possible (suspected)
Fewer of the typical clinical features
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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33. Meningococcal Disease — Case Definition
Clinical case definition
An illness with sudden onset of fever (>38.5°C rectal or >38.0°C axillary) and one or more
of the following: neck stiffness, altered consciousness, other meningeal sign or petechial or
puerperal rash.
Laboratory criteria for diagnosis
Positive cerebrospinal fluid (CSF) antigen detection or positive culture.
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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34. Case classification
Suspected: A case that meets the clinical case definition.
Probable: A suspected case as defined above and turbid
CSF (with or without positive Gram stain) or ongoing
epidemic and epidemiological link to a confirmed case.
Confirmed: A suspected or probable case with laboratory
confirmation.
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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35. Example: Case Definition
for Hepatitis A
Confirmed case:
– Anti-HAV IgM+
Probable case:
Pale skin
Suspect case:
Any two of the following:
Abdominal pain, fever, nausea, anorexia, malaise
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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36. 5. Find cases systematically & record
information
Target health care facilities where diagnosis is likely to be made
Enhanced passive surveillance e.g. letter describing situation and asking for reports.
Active surveillance e.g. phone or visit facility to collect information
Alerting the public
Media alert to avoid contaminated food products and seek medical attention if symptoms arise.
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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37. 5. Find cases systematically & record
information contd….
Identifying information
Name, address, and telephone number is essential if need to contact patients additional questions.
Also to Notify them of lab results and outcomes of investigation
Names also helps in checking for duplicate records while addresses allow for Mapping the geographic
extent.
Demographic information.
Provide “person” characteristics for defining population at risk
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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38. 5. Find cases systematically & record
information contd….
Clinical findings
Signs and symptoms allow to Verify that the case definition has been met
Date of onset is needed to Chart the time course of outbreak.
Reporter information
Id of person making report
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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39. 5. Find cases systematically & record
information contd….
Line listing
Abstraction of selected critical items
from above information
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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40. What is a Line Listing?
A rectangular database similar to spreadsheet
Provides summary of key data about cases in an outbreak
Each row represents one case
Each column represents one variable
First column usually identifier —name, initials, or ID number
Can be paper or electronic
Can be quickly reviewed and updated
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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46. 6. Perform Descriptive Epidemiology
After collection of data characterize
the outbreak by:
Time
Place
Person
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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47. Perform Descriptive Epidemiology
• What and why
–Provides systematic method
–Characterize, or describe what has occurred
–Person, place, time
useful for developing
hypotheses
• Components
–Line list
–Epi curve
–Others, but we will focus on line list and epi-curve
56
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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48. Tabulate and orient data
Create line listing
Person
Who was infected?
What do the cases have in common?
Place
Where were they infected?
May be useful to draw a map
Time
When were they infected?
Create an epidemic curve 03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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49. Time (Epidemic curve)
Epidemic curve
Histogram of the number of cases by their date of onset
Visual display of the outbreak’s magnitude and time trend
Common source vs. Propagated
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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50. Perform Descriptive Epidemiology
Line List•Person
•Place
•Time Epidemic curve (‘Epi curve’)
57
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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51. Perform Descriptive Epidemiology
58
• Epi curve: visual representation of
– Ill persons (cases) over time
– Magnitude of outbreak
– Type of outbreak
• Point source
• Propagated (person-to-person)
– Exposure period / Time of exposure (if agent known)
– Incubation period
– Possible agents (if time of exposure known)
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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52. Perform Descriptive Epidemiology
59
• How do I make an epi curve?
– Number of cases on the vertical (y) axis
– Time period (or date of illness onset) on the horizontal (x) axis
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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53. Example – X and Y axis
0
60
20
100
80
60
40
Y-
axis
Time
X-axis
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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54. Perform Descriptive Epidemiology
61
• How do I choose the correct unit of time?
– Depends upon the incubation period
– If incubation period is not known, graph several epi-curves with
different time units
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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55. Example Epi Curve – Time Unit (Day)
100
80
60
40
20
0
62
1-Apr
3-Apr
5-Apr
7-Apr
9-Apr
11-Apr
13-Apr
15-Apr
17-Apr
Time
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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56. Example Epi Curve – Time Unit (Hours)
100
80
60
40
20
0
63
6am
12N
6pm
12M
N
6am
12N
6pm
12M
N
Time
April 9 April 10
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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57. Perform Descriptive Epidemiology
69
• Propagated (person-to-person)
– Progressively taller peaks, an incubation period apart
– Person to person transmission
– May last a long time
– May have multiple waves
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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58. Example Epi Curve – Person to person
(Propagated)
Epi Curve…Person to Person
100
80
60
40
20
0
Time
70
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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59. Example Epi Curve – Person to person
(Propagated)
Epi Curve…Person to Person
100
80
60
40
20
0
Time
71
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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60. Example Epi Curve – Person to person
(Propagated)
Epi Curve…Person to Person
100
80
60
40
20
0
Time
72
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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61. Perform Descriptive Epidemiology
78
• Epi curve: visual representation of
– Ill persons (cases) over time
– Magnitude of outbreak
– Type of outbreak
• Point source
• Propagated (person-to-person)
– Exposure period / Time of exposure (if agent known)
– Incubation period
– Possible agents (if time of exposure known)
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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62. Example – Exposure Period
40
20
0
60
80
100
Time
Known
time of
Exposure
79
Average incubation
Exposure
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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64. Place (spot map, shaded map)
Geographic extent of problem
Clusters or patterns providing important etiologic clues
Spot maps
Where cases live, work or may have been
exposed
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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65. Person (Tables)
Determine what population at risk
Usually define population by host characteristics or exposure
Use rates to identify high-risk groups
Numerator = number of cases
Denominator = number of people at risk
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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66. 7. Develop Hypotheses
Hypotheses should address
Source of the agent
Mode of transmission
Vector or vehicle
Exposure that caused disease
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
66
67. Develop Hypotheses
• What are hypotheses?
– Statements which help us describe why and how the
outbreak occurred
• How do you generate hypotheses?
– Examine descriptive epidemiology: line list, epi-
curve
– Administer open-ended questionnaire to cases
– Review the existing body of knowledge
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
68. Develop Hypotheses
• Questions to ask yourself:
– What is the agent’s usual reservoir
– How is the agent usually transmitted
– What vehicles are commonly implicated
– What are the known risk factors
– In discussions with ill persons, what possible exposures were in
common
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
69. Example – Develop Hypothesis
• Case and clinical information:
– Acute gastroenteritis
– Most aged 14 – 18 years
– 307 ill persons (cases)
– Onset of illness: 12am Feb 12 – 10am Feb 14
• Common exposures:
– Attending youth conference
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
70. Example: Cases of Gastroenteritis by Time of
Symptom Onset (n=307)70
60
50
40
30
20
10
0
11-Feb 12-Feb 13-Feb 14-Feb
Date and Time of Illness Onset
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
71. Example: Cases of Gastroenteritis by Time of
Symptom Onset (n=307)
50
40
30
20
10
0
60
70
11-Feb 12-Feb 13-Feb 14-Feb
Date and Time of Illness Onset
Banquet dinner
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
72. Example: Cases of Gastroenteritis by Time of
Symptom Onset (n=307)
40
30
20
10
0
50
60
70
11-Feb 12-Feb 13-Feb 14-Feb
Date and Time of Illness Onset
Banquet dinner
Catered
lunch
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
73. Example: Cases of Gastroenteritis by Time of
Symptom Onset (n=307)
20
10
0
30
40
50
60
70
11-Feb 12-Feb 13-Feb 14-Feb
Date and Time of Illness Onset
Banquet dinner
Catered
lunch
Catered
breakfas
t
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
74. Example: Cases of Gastroenteritis by Time of
Symptom Onset (n=307)
20
10
0
30
40
50
60
70
11-Feb 12-Feb 13-Feb 14-Feb
Date and Time of Illness Onset
Banquet dinner
Catered
lunch
Catered
breakfas
t
Pizza
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
75. Example: Cases of Gastroenteritis by Time of
Symptom Onset (n=307)
20
10
0
30
40
50
60
70
11-Feb 12-Feb 13-Feb 14-Feb
Date and Time of Illness Onset
Banquet dinner
Catered
lunch
Catered
breakfas
t
Pizza
Laboratory
Testing
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
76. Example: Cases of Gastroenteritis by Time of
Symptom Onset (n=307)
20
10
0
30
40
50
60
70
11-Feb 12-Feb 13-Feb 14-Feb
Date and Time of Illness Onset
Banquet dinner
Catered
lunch
Catered
breakfas
t
Pizza
Laboratory
Testing 4 / 9
norovirus +
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
77. Example: Cases of Gastroenteritis by Time of
Symptom Onset (n=307)
20
10
0
30
40
50
60
70
11-Feb 12-Feb 13-Feb 14-Feb
Date and Time of Illness Onset
Banquet dinner
Catered
lunch
Catered
breakfas
t
Pizza
Norovirus:
24 hour incubation
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
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78. Example – Initial
Hypothesis
• We hypothesize that:
– norovirus was the causative agent of the outbreak, and
– eating breakfast served on February 12 was the most likely
exposure to norovirus
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
79. Example: Cases of Gastroenteritis by Time of
Symptom Onset (n=307)
20
10
0
30
40
50
60
70
11-Feb 12-Feb 13-Feb 14-Feb
Date and Time of Illness Onset
Banquet dinner
Catered
lunch
Catered
breakfas
t
Pizza
Epidemiology
Norovirus:
24 hour incubation
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
80. Example: Cases of Gastroenteritis by Time of
Symptom Onset (n=307)
20
10
0
30
40
50
60
70
11-Feb 12-Feb 13-Feb 14-Feb
Date and Time of Illness Onset
Banquet dinner
Catered
lunch
Catered
breakfas
t
Pizza
Epidemiology:
Breakfast:
RR=1.1Dinner: RR=2.6
Norovirus:
24 hour incubation
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
81. Example: Cases of Gastroenteritis by Time of
Symptom Onset (n=307)
10
0
20
30
40
50
60
70
11-Feb 12-Feb 13-Feb 14-Feb
Date and Time of Illness Onset
Banquet dinner
Catered
lunch
Catered
breakfas
t
Pizza
Lab = Norovirus
Epi = Incubation
period too short for
norovirus
Norovirus:
24 hour incubation
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
82. Example: Cases of Gastroenteritis by Time of
Symptom Onset (n=307)
20
10
0
30
40
50
60
70
11-Feb 12-Feb 13-Feb 14-Feb
Date and Time of Illness Onset
Banquet dinner
Catered
lunch
Catered
breakfas
t
Pizza
What has an
incubation period
this short?
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
83. Norovirus
Infection
• RNA virus
• Resistant to environmental stress
• Incubation period usually 24 hours with range 12-72
hours
• Causes GI illness with watery diarrhea and >50% vomiting
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
84. Clostridium perfringens
Toxicoinfection
• Spore-forming Gram positive rod
– Arises after consumption of bacteria-containing food
– Toxin produced within the small intestine following ingestion
• Diarrhea predominant illness with little vomiting
• Incubation period usually 6–12 hours
• Associated with poorly cooked meat
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
85. Example – Additional Lab
Information
• Norovirus testing
– Reverse transcription PCR (RT-PCR)
– Sent to CDC for confirmation
• Clostridium perfringens enterotoxin
testing
– Oxoid toxin detection kit
– PCR
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
86. Example – Additional Lab
Information
• Testing did not confirm the presence of norovirus
• After 4 weeks at 4°C, stool tested for Clostridium
perfringens
enterotoxin
– Toxin present in 8 of 9 specimens tested
– Enterotoxin gene detected in 5 of 6 specimens tested
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
87. Example – Final
Hypothesis
• We hypothesize that:
– Clostridium perfringens toxicoinfection was the causative agent
of this point source outbreak
– Associated with consumption of inappropriately-cooked
chicken at the dinner served on February 12
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
88. Develop Hypotheses
• Questions to ask yourself regarding
hypothesis:
– Is hypothesis stated in a way that can be ‘tested’
– Does it address:
• agent
• vehicle / source
• mode of transmission
• exposure that caused illness
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
89. Test the Hypothesis
• We hypothesize that:
–Clostridium perfringens toxicoinfection was the causative
agent of this point source outbreak
–Associated with consumption of inappropriately-cooked
chicken at the dinner served on February 12
• Testable
• Agent
• Vehicle or source of agent
• Mode of transmission
• Exposure
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
90. Evaluate Hypotheses
105
• Two methods:
– Compare hypothesis with established facts
– Perform additional studies (e.g., analytic)
• Cohort or case-control
• Assess exposures equally among ill and non-ill persons
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
90
91. Evaluate Hypotheses
106
• Compare hypothesis with established facts
– Evidence is so strong that hypothesis does not need to be tested
– E.g., Salmonella Paratyphi B with PFGE pattern .1228 (the
outbreak strain) isolated from unpasteurized tempeh
– E.g., norovirus identified in a nursing home; norovirus is known
to be circulating in the community
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
91
92. 7. Perform Additional Studies
Used when the relationship between exposure and
disease is less clear
93. Value of Analytic Studies
• Support for specific public health action (e.g., recall)
• Describe new diseases, learn more about known
diseases
• Address public and political concern
• Develop strategies to prevent future outbreaks
• Fulfillment of legal obligations and duty of care for
the public 03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
94. Perform Additional Studies
• Cohort
– Able to identify every person in group (‘cohort’)
– Possible when group is well defined
– Include EVERYONE who could have been exposed
• E.g., Meeting attendees, students, wedding reception,
LTCF residents
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
95. Perform Additional Studies
110
• Case-control
– Compare exposures among ill persons (case) and non-ill persons (controls)
– Used when a complete list is not available or too large
– Controls are sample of same population from which cases
arose (e.g., source population)
• E.g., same city, attend same restaurant
– If a control had developed illness, would have been included as
a case
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
95
96. 10. Implement Control /Prevention
Measures
Implement control measures as soon as possible
May be aimed at agent, source, or reservoir
eliminate the source
interrupt transmission
reduce susceptibility
Create mechanism to evaluate both short and long-term
effectiveness of control / prevention measures
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
96
97. 8. Implement Control
Measures
• Required response from public health
• Can occur at any point during the outbreak
• Prevent further exposure, future outbreaks
• Should be guided by epidemiologic results in
conjunction with environmental investigation
• Performed in conjunction with DPH, regulators,
industry, other agencies
• Balance between preventing further disease,
protecting credibility and reputation of institution
• Identify one person to communicate control measures
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
98. Example – Control Measures
• Summary:
– Attendees at a youth conference
• > 1,000 attendees
• 307 ill persons (cases)
– Clostridium perfringens toxicoinfection
– Associated with inappropriately cooked chicken
• Recommended control measures?
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
99. 11. Communicate Findings
Oral briefing for local authorities
Local health authorities and persons responsible for implementation of control and
prevention measures
Written reports;
that follows intro, background, methods, results, discussion and
recommendations.
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
99
100. Communicate Findings
120
• Public and media:
– Single member of team should interact with media, communicate progress and
findings
– Media attention desirable if public action is needed
– Response to media attention important to address public
concerns about outbreak
– Opportunity to educate community
– Single overriding communication objective (SOCO)
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
100
101. Communicate Findings
• Daily updates (Situation Reports)
–Narrative
• Number of persons ill
• Number of persons potentially exposed (if known)
• Range of onset dates
• Type of symptoms
• Available laboratory results
• Number hospitalized / died
• Actions already taken
–Action Items
• Summary of recommendations and plans for surveillance, control
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
104. Maintain Surveillance
126
• Evaluate / document effectiveness of control measures
• To ensure outbreak is over
• To ensure secondary outbreak is not occurring
• It is recommended to maintain surveillance for 2 average incubation
periods following the last date of illness onset
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
104
105. Conclusions
• Epidemiologic investigations essential component of
public health, present opportunities to:
– Characterize diseases
– Identify populations at risk
– Evaluate programs, policies, or existing prevention strategies
– Train public health staff
– Educate the public
– Fulfill legal obligations and duty of care for the public
• 10 steps provide systematic framework necessary to
investigate any outbreak
03/10/19Prof: Dr Muhammad Tauseef Jawaid King Khalid University KSA
106. References
Michael Gregg. Field Epidemiology. 2nd
edition. Oxford University Press, 2002.
Control of Communicable Disease in Man,
17th edition. Chin, J (ed). APHA, 2000.
Principles & Practice of Infectious Diseases,
5th edition. Mandell GL, Bennett JE, Dolin R
(eds). Churchill Livingstone; 2000
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106
Editor's Notes
This presentation will provide a general overview of the basic steps of disease outbreak investigations, and explain factors that may contribute to a decision to investigate. We will present Dr. John Snow’s seminal work during the 1854 cholera outbreak in London as an example of how to conduct an outbreak investigation.
Outbreak investigations afford a number of opportunities for health department personnel. First, outbreaks provide an opportunity to characterize a public health problem. For example, the investigation of 15 confirmed Salmonella cases in Minnesota uncovered a nationwide outbreak associated with consumption of Schwan’s ice cream that may have gone undetected. This product was estimated to cause 224,000 cases of salmonellosis.
Second, investigation may identify risk factors that are associated with infection that are preventable. Epidemiologic investigations of Escherichia coli O157:H7 outbreaks have identified consumption of foods such as pink hamburgers, unpasteurized apple juice, or alfalfa sprouts that consumers may avoid to reduce their risk of illness.
Third, outbreak investigations may provide new research insights into the disease even if no new cases are occurring. In 1986, identification of a small outbreak of chronic diarrheal illness of unknown etiology associated with consumption of unpasteurized milk has led to intense laboratory research into the presumed infectious agent of “Brainerd” diarrhea.
Finally, outbreak investigations provide opportunities for training of health department staff in methods of public health investigation and emergency response that are essential in the era of potential bioterrrorism events.
Deciding to investigate is the crucial early step. Availability of resources and trained personnel should factor into this decision, especially since the direct costs of an investigation are considerable. Once the decision to investigate is made, the team leader will then begin to assemble team members. The team leader may be selected as a result of the outbreak setting or etiologic agent. Initially, the investigation may be led by an epidemiologist or clinician who will assume responsibility for the first stages of the outbreak (verifying the diagnosis and existence of the outbreak). Personnel will likely be added as the outbreak progresses, but availability of trained personnel should factor into the decision to investigate. Ideally, the team leader will assemble the team, present available information, outline the plan for investigation, and assign roles and responsibilities to the team members early in the investigation.
The team leader should have experience in outbreak investigation and public health epidemiology. Depending on the size and organization of the health department, this could be the local health director, public health nurse, epidemiologist, or environmental health specialist.
The epidemiologist has expertise in various aspects of outbreak investigations, from choosing the study design and questionnaire development to creating a database and conducting data analysis.
A microbiologist, usually at a state or regional public health laboratory, will be important in verifying the diagnosis and subtyping of pathogens to help refine a case definition.
Environmental health specialists (EHS) or sanitarians are important in preventing foodborne outbreaks from occurring through routine inspections of food preparation facilities, health education, and training of foodhandlers. However, once an outbreak occurs, sanitarians are able to identify food safety issues that may have contributed to the outbreak, such as time and temperature violations, and can assist in proper collection of food and environmental samples. An EHS may also provide guidance on food safety regulations and engineering during the outbreak.
Interviewers will be used to collect data, either in person or by telephone. Interviewers can come from the ranks of the health department personnel, including clerical support staff; in large outbreaks, state or federal personnel or students in medicine or public health may be recruited to conduct interviews.
Clinicians may be necessary to administer vaccines or prophylactiv therapies, or to assist in collection of clinical specimens from case-patients. Clinicians may come from the health department or the local medical community. Zoonotic outbreaks may involve veterinarians and other scientists, such as entomologists, to provide expertise in animal reservoirs or vectors.
Regulators from state or federal agencies may be included on the outbreak team to help facilitate identification of the source of contaminated food items and develop prevention strategies through enforcement of food safety regulations.
One person from the team should be designated as the media spokesperson to make sure that clear and consistent messages are transmitted to the public. This is especially important if the outbreak is ongoing or there is anxiety among the public, such as during a suspected bioterrorism event.
Some questions to keep in mind as an outbreak unfolds are:
Other questions to consider during outbreaks are:
Proper equipment is necessary for a successful outbreak investigation. Health departments should have a functioning computer with access to the internet for email and literature searches through PubMed. Epi Info is a software package that is useful for entry and analysis of epidemiologic data; it is available for free from the Centers from Disease Control and Prevention (CDC) website.
A cooler to transport specimens, rectal swabs or specimen cups to collect specimens, and phlebotomy equipment for collecting blood samples are useful equipment to have in a local health department for specimen collection .
The CDC’s Foodborne and Diarrheal Disease website offers helpful guidelines for confirming the diagnosis, specimen collection, and a sample questionnaire for use in specimen collection for foodborne disease outbreaks.
Team leaders should receive regular updates to measure progress in the investigation; they should use this information to provide feedback and direction to the team members. Concurrently, leaders should make task checklists and assign specific roles and responsibilities to team members.
During outbreak investigations, keeping the lines of communication open through regular meetings or phone calls is crucial. Management of outbreaks that occur in multiple jurisdictions rely on communication among local, state, and federal public health agencies.
Documentation of progress is important for keeping all team members up to date and helpful for drafting the final report.
As a field investigator, you must have the appropriate scientific knowledge, supplies, and equipment to carry out the investigation before departing for the field. Discuss the situation with someone knowledgeable about the disease and about field investigations, and review the applicable literature. In previous similar outbreaks, what have been the sources, modes of transmission, and risk factors for the disease? Assemble useful references such as journal articles and sample questionnaires.
Before leaving for a field investigation, consult laboratory staff to ensure that you take the proper laboratory material and know the proper collection, storage, and transportation techniques. By talking with the laboratory staff you are also informing them about the outbreak, and they can anticipate what type of laboratory resources will be needed.
You also need to know what supplies or equipment to bring to protect yourself. Some outbreak investigations require no special equipment while an investigation of SARS or Ebola hemorrhagic fever may require personal protective equipment such as masks, gowns, and gloves.
A case definition is a 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. The clinical criteria should be based on simple and objective measures such as "fever ≥ 40°C (101°F)," "three or more loose bowel movements per day," or "myalgias (muscle pain) severe enough to limit the patient's usual activities. " The case definition may be restricted by time (for example, to persons with onset of illness within the past 2 months), by place (for example, to residents of the nine-county area or to employees of a particular plant) and by person (for example, to persons with no previous history of a positive tuberculin skin test, or to premenopausal women). Whatever the criteria, they must be applied consistently to all persons under investigation.
It is important to create a line listing of confirmed, probable, and possible cases. An epidemic curve can orient the data by time and provide evidence of the outbreak. The shape of the curve can be used to determine the type of outbreak (e.g. point source or person-to-person transmission) and if the outbreak is ongoing.
Snow first created a line listing of case-patients, including age, gender, and address. These cases were plotted on a map and it was observed that they occurred in proximity to the pump on Broad Street.
Additional references used during this presentation are listed in the periodical FOCUS on Field Epidemiology, issue #1: An Overview of Outbreak Investigations