Investigation of Epidemic - by Dr.Sujatha Sathananthan

1. Investigation of Epidemic
Dr.S.Sujatha MD.,DPH.,
Assistant Professor,
Department of Community Medicine
Chengalpattu Medical College

2. 12 May 2018 2Chengalpattu Medical College

3. Spot Map
12 May 2018 3Chengalpattu Medical College

4. 12 May 2018 4Chengalpattu Medical College

5. 12 May 2018 5Chengalpattu Medical College

6. Vibrio Cholera
Robert Koch
Vibrio Cholera 1883
Filippo Pacini
Vibrio Cholera 1854
12 May 2018 6Chengalpattu Medical College

7. What is an outbreak ?
Occurrence of more cases of disease than
expected
in a given area
among a specific group of people
over a particular period of time
12 May 2018 7Chengalpattu Medical College

8. Why investigate outbreaks?
 Stop the outbreak
Find and neutralise the source (cause)
Prevent additional cases
 Prevent future outbreaks
 Improve surveillance and outbreak detection
 Improve our knowledge
 Keep the public’s confidence
12 May 2018 8Chengalpattu Medical College

9. Specific Demands
When Investigating Outbreaks
 Unexpected event
 Act quickly
 Rapid control
 Bias caused by media reports
 Legal and financial pressure
 Interdisciplinary coordination
 Work carried out in the field
12 May 2018 9Chengalpattu Medical College

10. Steps of an Outbreak Investigation
1. Verification of Diagnosis
2. Confirmation of the existence of an Epidemic
3. Define a case , population at risk
4. Rapid search of all cases & obtain information
5. Describe data collected and data analysis
6. Develop hypothesis
7. Test hypothesis: analytical studies
8. Evaluation of Ecological Factors
9. Further investigation of population at risk
10. Communicate results,
including outbreak report
control measures & preventive measures
12 May 2018 10Chengalpattu Medical College

11. Detection
Routine surveillance
Clinical / Laboratory
General public
Media
12 May 2018 11Chengalpattu Medical College

12. Confirm outbreak and diagnosis
Is this an outbreak?
• More cases than expected?
• Surveillance data
• Surveys: hospitals, labs, physicians
12 May 2018 12Chengalpattu Medical College

13. Confirm outbreak and diagnosis
• Laboratory confirmation
– serology
– isolates, typing of isolates
– toxic agents
• Contact (visit) the laboratories
• Meet attending physicians
• Examine some cases
Not always necessary to confirm all the cases
but confirm a proportion
throughout the outbreak
12 May 2018 13Chengalpattu Medical College

14. Outbreak confirmed 
Immediate control
measures?
Further
investigation?
Treatment
prophylaxis
exclusion / isolation
public warning
hygienic measures
others
aetiological agent
mode of transmission
vehicle of transmission
source of contamination
population at risk
exposure causing illness
12 May 2018 14Chengalpattu Medical College

15. Team coordinates
field investigation
Outbreak confirmed,
further investigations warranted
Form Outbreak
Control Team?
12 May 2018 15Chengalpattu Medical College

16. Identify &
count cases
notifications
laboratories
hospitals, GPs
schools
workplace,
cases,
media, etc

17. Identify &
count cases
Obtain
information
Identifying information
Demographic information
Clinical details
Exposures and known risk
factors

18. Identify &
count cases
Obtain
information
Analysis of descriptive
data
Describe in
 time
 place
 person

19. Descriptive epidemiology
- Who are the cases? (person)
- Where do they live? (place)
- When did they become ill? (time)
12 May 2018 19Chengalpattu Medical College

20. Epidemic Curve
• Histogram
• Distribution of cases by time of onset of symptoms,
diagnosis or identification
– time interval depends on incubation period
12 May 2018 20Chengalpattu Medical College

21. Epidemic curve
Describe
start, end, duration
peak
importance
atypical cases
Helps to develop hypotheses
incubation period
etiological agent
type of source
type of transmission
time of exposure
12 May 2018 21Chengalpattu Medical College

22. Point Source Epidemic- Food poisoning
12 May 2018 Chengalpattu Medical College 22

23. Continuing Common Source- Gonorrhoea
outbreak by a prostitute
12 May 2018 Chengalpattu Medical College 23

24. Intermittant outbreak- by a carrier of
Pseudomonas aeruginosa
12 May 2018 Chengalpattu Medical College 24

25. Propagated Epidemic- Hepatitis A and Polio
12 May 2018 Chengalpattu Medical College 25

26. Place
 Place of residence
 Place of possible exposure
– work
– meals
– travel routes
– day-care
– leisure activities
 Maps
– identify an area at risk
12 May 2018 26Chengalpattu Medical College

27. Distribution of cases of cholera,
London 1854
12 May 2018 27Chengalpattu Medical College

28. Person
 Distribution of cases by age, sex, occupation,etc
(numerator)
– 60 female
– 50 male
 Distribution of these variables in population
(denominator)
– 600 females
– 350 males
 Attack rates
– female: 60/600
– Males: 50/350
12 May 2018 28Chengalpattu Medical College

29. Develop hypotheses
- Who is at risk of becoming ill?
- What is the disease?
- What is the source and the vehicle?
- What is the mode of transmission?
12 May 2018 29Chengalpattu Medical College

30. Compare hypotheses
with facts
Test specific hypotheses
Analytical studies
- cohort studies
- case-control studies
12 May 2018 30Chengalpattu Medical College

31. Verify hypothesis
Special investigations/studies
 Microbiological investigation
 Environmental investigation
 Trace back investigations (origin of foods)
 Entomological investigations
12 May 2018 31Chengalpattu Medical College

32. Implement control measures
1) Control the source of pathogen
2) Interrupt transmission
3) Modify host response
At first, general measures
According to findings, more
specific measures
12 May 2018 32Chengalpattu Medical College

33. Outbreak report
 Regular updates during the investigation
 Detailed report at the end
 communicate public health messages
 influence public health policy
 evaluate performance
 training tool
 legal proceedings
12 May 2018 33Chengalpattu Medical College

34. Writing the report

35. 35

36. Role of the Epidemiologist
 Systematic Description
 Identification of risk factors (by descriptive or
analytical means)
 Identification of interventions
 Work with others to implement control measures
 Evaluate the impact of control measures
12 May 2018 36Chengalpattu Medical College

37. Steps of an outbreak investigation
1. Verification of Diagnosis
2. Confirmation of the existence of an Epidemic
3. Define a case , population at risk
4. Rapid search of all cases & obtain information
5. Describe data collected and data analysis
6. Develop hypothesis
7. Test hypothesis: analytical studies
8. Evaluation of Ecological Factors
9. Further investigation of population at risk
10. Communicate results,
including outbreak report
control measures & preventive measures
12 May 2018 37Chengalpattu Medical College

38. • z
12 May 2018 38Chengalpattu Medical College