steps involved in investigation of epidemics with examples

1. Investigation of Epidemic
Presentor: Dr. Mamta Gehlawat
Moderator: Dr. Gautam Roy 6/17/2015 1
ART OVER FEAR OF CHOLERA IN 19TH CENTURY

2. Outline
1. What is an Epidemic?
2. Objectives of investigation of Epidemic
3. How to investigate an Epidemic?
4. Steps in detail
5. Examples
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3. What is an Epidemic ?
• Epidemic - The occurrence in community or region of a
group of illnesses of similar nature, clearly in excess of
normal expectancy and derived from a common or
propagated source1
• Outbreak - An Epidemic limited to localised increase in
the incidence of disease2
1. Epidemiology 4th ed, Gordis
2. A Dictionary of Epidemiology 3rd ed, Last JM
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4. Objectives of investigation
1. Define magnitude /involvement
2. Determine factors responsible
3. Identify i) Source
ii) Mode of transmission
iii) Control measures
4. Prevent recurrence
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5. How to investigate
1. Prepare for field work
2. Verify the diagnosis
3. Establish the existence of an outbreak
4. Construct a working case definition
5. Find cases systematically & record information
6. Perform descriptive epidemiology
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6. 7. Develop hypotheses
8. Evaluate hypotheses epidemiologically
9. Reconsider,refine & reevaluate hypotheses
10. Compare & reconcile with lab & environmental studies
11. Implement control & prevention measures
12. Initiate/ maintain surveillance
13. Communicate findings 6/17/2015 7
How to investigate

7. STEP1#
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Prepare for field work

8. Prepare for field work
Two aspects of preparation before leaving for field work-
A. Scientific & investigative issues
I. Ensure proper laboratory material with proper
collection ,storage & transportation techniques
II. Equipments for self protection
III. Plan of action with clear primary ,secondary &
tertiary objectives
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9. Prepare for field work
B. Management & operational issues
I. Selection of team members & sorting of their roles
& responsibilities in the field
II. Local staff & local contacts who will be involved
III. A communication plan with officials & public
IV. Arrange electronic items, travel, lodging & local
transportation within budgets allotted for the
investigation
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10. STEP 2
Verify the diagnosis
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11. Verify the diagnosis
1. Important as control measures are disease specific
2. Review clinical & lab findings
3. A qualified physician to correlate diagnosis & patient
history & clinical findings
4. Summarize clinical features with frequency distribution
to characterize spectrum of illness
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12. STEP3#
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Establish the existence of an outbreak

13. Establish the existence of an outbreak
1. To verify that a cluster of cases is indeed an outbreak
2. Expected number is the number from the previous few
weeks or months, or the previous few years.
i) For a notifiable disease – health department surveillance
records
ii) For other diseases and conditions – locally available
data
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14. Establish the existence of an outbreak
3. May not be an outbreak
i) excess reporting compare to before
ii) misdiagnosis / lab error
iii) sudden change in population size
4. Also noted i) severity of illness
ii) potential for spread
iii) availability of control measures
iv) political interest
v) available resources 6/17/2015 15

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17. STEP4#
Construct a working case definition
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18. Construct a working case definition
1. A case definition is a standard set of criteria for deciding
whether an individual should be classified as having the
health condition of interest
2.Includes clinical criteria
& restrictions by
-time
-place
-person
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19. Construct a working case definition
1. Case definition must not include the suspected
exposure or risk factor
2. Create different categories of a case definition, such as
confirmed, probable & possible or suspect, that allow for
uncertainty of diagnoses
3. Confirmed- lab verified
4. Probable- typical clinical features without lab verification
5. Possible- less typical clinical features
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21. Construct a working case definition
1. Only few case definitions are 100% accurate
2. Infected people who have mild or no symptoms are often
missed
as they have little reason to be tested
3. Some investigations begin with a relatively specific
or narrow case definition
eg. AIDS & SARS
-to accurately characterize the typical clinical features of the
illness, risk factors for illness & cause of the illness.
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22. STEP5#
Find cases systematically &
record information
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23. Find cases systematically
& record information
1. Look thoroughly for cases to determine the true geographic
extent & the populations affected
2. In clinics, hospitals & labs by
i) Passive surveillance by sending a letter asking for
reports
of similar cases
ii) Active surveillance by telephoning or visiting the
facilities
3. Public alerted by local media
4. Ask case-patients if they know others with same condition6/17/2015 24

24. Find cases systematically
& record information
5. Data collection / generic case report form including-
i. Identifying information -name, address, number
ii. Demographic information -age ,sex ,race, occupation
iii. Clinical information -signs and symptoms, onset,
duration, outcome
iv. Risk factor information -food /water sources etc
v. Reporter information -Dr/ clinic /hospital /lab
6. Selected critical items are put on a form called line listing
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25. s
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26. STEP6#
Perform descriptive epidemiology
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27. Perform descriptive epidemiology
• Descriptive epidemiology is a process in which the outbreak
is characterized by time, place & person
• Importance-
i. characterizes the outbreak with time , place & person
ii. identifies population at risk
iii. clues about etiology ,source, mode of transmission
iv. tells disease is where & to whom
v. familiarizes with the data
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28. Perform descriptive epidemiology (time)
i. Easy to understand
ii. Pattern of spread
iii. Course of epidemic
iv. Evaluation & answering questions
v. Outliers
vi. Find probable time of exposure
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Epidemic curve - a special type of histogram used to
depict the time course of an epidemic (needs date/time of
onset)

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Perform descriptive epidemiology (place)

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AREA MAP –EHRLICHIOSIS IN WISCONSIN

37. Perform descriptive epidemiology (person)
1. Age
2. Sex
3. Exposures
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38. STEP7#
Develop hypotheses
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39. Develop hypotheses
1. Begins long before in reality
2. Hypotheses :
i. source
ii. mode of transmission
iii. exposures causing disease
iv. testable
v. previous knowledge of disease
vi. clues from case patients
vii. local staff’s opinion
viii. epidemic curve
ix. ?bioterrorism
x. outliers
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40. STEP8#
Evaluate hypotheses epidemiologically
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41. Evaluate hypotheses epidemiologically
1. Comparing with facts - when evidences support
hypothesis
2. Using Analytic Epidemiology- form comparison group
- test causal relationship
Retrospective case control
cohort study
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43. STEP9#
Reconsider, refine & reevaluate hypotheses
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44. Reconsider, refine & reevaluate
hypotheses
1. If hypotheses not good – analytical studies unrevealing
2. Rethink hypotheses – consider new links in cases/modes
- more closely matched control group
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45. STEP10#
Compare & reconcile with
Lab & environmental studies
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46. Compare and reconcile with lab
& environmental studies
1. Lab – to confirm findings
2. Environment – explains cause of outbreak
eg.
consumption of beverages with ice purchased from a vendor
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47. STEP11#
Implement control & prevention measures
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48. Implement control and prevention
measures
1. Implemented as early as possible in practice
2. Even before the investigation starts
3. Confidentiality issues – avoid stigma
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49. Implement control and prevention
measures
4. Directed to –
a) Agent eg. TB treatment of case
b) Source eg. soil decontamination to kill agent
c) mode of transmission eg. influenza patients in separate area
a) Entry portal eg. bed nets to avoid mosquito bites
b) Host eg. Vaccination / prophylactic drugs
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50. STEP12#
Initiate or maintain surveillance
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51. Initiate or maintain surveillance
• Active surveillance-
1. whether control and preventive measures are working
2. Whether outbreak has spread outside original area
if yes
effective disease control and prevention measures must be
implemented in these new areas
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52. STEP13#
Communicate findings
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53. Communicate findings
1. Oral briefing for local authorities
2. Written report in scientific format
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54. Example from India
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Jaundice outbreak in the Girdharnagar ward, Ahmedabad,
India, 2008

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Jaundice cases in the Girdharnagar ward, Ahmedabad
2008

56. 6/17/2015 59ART ABOUT PLAGUE IN OLD TIMES
THANK YOU…