OutbreakInvestigation By medical year 3 UMMG.pdf

About outbreak investigation

1. Medical year -3
UMMG

2. DEFINITION OF OUTBREAK
Occurrence of morecases of disease
than expectedin a given area
among a specific group of people
over a particular period of time (or)
Two or more linked cases of the same illness.
(or)
Single case –Emerging or Re-emerging disease in that area

3. Epidemic and Outbreak
Outbreak
A sudden increase in the number of cases of a disease in a specific area,
such as a small group or thousands of people across a continent.
Outbreaks are usually used when diseases happen in a more limited
geographic area.
•Epidemic
A more widespread outbreak.
An outbreak becomes an epidemic when it spreads quickly to more people
than experts would expect and moves into a large geographic area.

4. Why Outbreaks occur?
due to shift in the existing balance between agent,
host and environment

5. OBJECTIVES OF OUTBREAK INVESTIGATIONS
1.To controlthe current outbreak
2.To prevent occurrence of future outbreak
3.To evaluate the effectivenessof prevention programs
4.To evaluate the effectiveness of the existing surveillance
5.To trainhealth professionals
6.To do research for more knowledge of the diseases
7. To respondto public or political or legal concern

6. STEPS OF AN OUTBREAK INVESTIGATION
1.Prepare for Field Work: Rapid Response Team
2.Verification of diagnosis Confirmation of the existence of an
outbreak
3. Define case and start case-finding
4. Descriptive data collection and analysis
5. Develop hypotheses

7. STEPS Cont:
6.Analytical studies to test hypotheses (Testing of
hypothesis)
7.Evaluation of ecological factors
8.Communicate conclusions and recommend control
measures
9. Implement control measures
10. Follow-up the control implementations
11. Report

8. 1.Investigation team should establishedbefore leaving to field
2.Investigation team should includefield epidemiologists, competent,
principal investigator
3.Team members consists of people experienced
•food and environmental sanitation
•vector control
•vaccination
•Veterinarian
•laboratory technicians
4. Administrator-good at providing logistic support, mobilizing
resources and providing administrative expertise
Step1.Prepare for Field Work: Rapid Response Team

9. Step1.Prepare for Field Work: Rapid Response Team
5. Preparationcan be grouped into three categories:
1.investigation
2.administration
3.consultation

10. Epidemiologist (Competent PI)
Environmental specialist
Microbiologist
Ministry/Government
Media
vector control
Vaccinator
Veterinarian
Outbreak
Investigation
Team?
FIELD
Preparation
1.investigation
2.administration
3.consultation
Administration
1.Logistic support
2.Mobilize resource
3.provide experte

11. Step 2.Confirm existence of an epidemic
1. Outbreak news can be obtainedby
surveillance data, media, healthcare provider or community
2. Verification is important
3. Compare with definition
•no. of cases (observed frequency) > expected no.
(based on past experience)
•Reporttrue or spurious
•C/F is usually sufficient (lab Dxput forward)

12. Step 2.Confirm existence of an epidemic
•4. Verification
•-should review clinical findings & laboratoryresults
•any questions about the findings, qualified laboratory staffs ,qualified
clinician should do
•(All sources should be systematically tracked and further investigated
to determine whether reports of suspected cases or outbreaks are
accurate.)

13. Routine surveillance
Clinical/Laboratory
General public media,community
Detection
Is this an outbreak?
Diagnosis verified?
Clinical & laboratory link between cases?
compare with definition -Expected numbers?
Any question -consult with qualified clinician, qualified lab technician

14. Excess of normal expectancy
•more than 5 yr median ( OR)
•more than average no. + 2SD of previous 5 yrs (OR)
•more than average no. of previous 2 wks or mths
2 cases with epi linkage in short time (2 cases within 1 IP)
1 case of a new emerging disease eg. Pneumonic plague, Avian Flu

15. Step 3.Define and identify cases
•DefineCase definition
•Identify case finding -Descriptive Epidemiology
(search for their characteristics)

16. CASE DEFINITION
•Standard set of criteria for deciding whetheranindividualshould
be classified as having the health condition of interest”.
•include -Clinical criteria, restrictions of time, place, person.
•Simple, practical objective
•suspect usually few typical clinicalfeatures
•probable usually has typical clinical features without laboratory
confirmation.
•confirmed, usually has laboratoryverification

17. Case finding
•By health facilities (hospital ,laboratories)
•By active surveillance
•By passive surveillance
•By active case finding

18. 4. Descriptive data collection and analysis
•By survey questionnaire
•Collect at least 4 types of information
(i) Identifyinginformation
(ii) Demographic information
(iii)Clinical information
(iv)Suspected riskfactors

19. Descriptive data collection and analysis
•Analysis
•In terms of time ,place, persons
•done using indices rather than absolutenumbers
•compare and determine populations & areas of highest risk
•also produce information for hypothesis formation to explain how
and why the outbreakhappened.

20. Identify &
count cases
Obtain
information
Perform
descriptive
epidemiology
Orient cases in;
time
place
person
Step 4-Descriptive data
collection and analysis

21. 5.Develop hypothesis
•results of descriptive analysis, information should be carefully
evaluated and used for developing ahypothesis.
•Questions that lead to the hypotheses formulationinclude:
What is the source and vehicle ofinfection?
What are the risks factors for an individual to get thedisease?
What is the level of vaccineeffectiveness?
What are the determinants of the outbreak or the factors which
when combined together result in theoutbreak?

22. 5.Develop hypothesis
Compare hypothesis with facts
Who is at risk of becoming ill?
What is the disease causing the outbreak?
What is the source and the vehicle?
What is the mode of transmission?

23. 6. Analytical studies to test hypotheses
•select an appropriate analytical study design.
•Common designs for hypothesis testing in outbreak investigations are
either a case-control or a historical cohort study.
•In the analytical study, a case definition may be more specific than
used for descriptive study in order to reduce misclassifying non-cases
as cases.

24. 6.Test hypothesis
CASE CONTROL TOTAL
EAT 13 4 17
NON-EAT 1 62 63
OR=201
EAT was 201 times more likely to be ill than NE

25. CasePatients ControlsTotal
AteatRestaurantA?
Yes a=30 b=36 66
No c=10 d=70 80
Total: 40 106 146
Odds Ratio for Restaurant A=ad/ bc
=30x70 /36x 10 = 5.8
This means that people who ate at Restaurant A were 5.8 times more likely
to develop hepatitis A than were people who did not eat there.

26. Food Attack Rate among people
who ate
AttackRate among
People whodid not eat
Attack Rate Ratio
(Risk Ratio)
Baked ham 63% 59% 1.1
Spinach 60% 62% 1.0
Cabbage salad 64% 60% 1.1
water 54% 65% 0.8
Ice cream, vanilla 80% 14% 5.7
Ice cream, chocolate 53% 74% 0.7
Milk 50% 62% 0.8
Coffee 61% 61% 1.0
Cakes 67% 54% 1.3

27. 7.Environmental and laboratory studies
•evidence to support and explain the epidemiological evidence
•take a photograph of working or environmental conditions
•reveal the clues that the causative agent
•select appropriate laboratory tests to aid an investigation
•Laboratory study is important to confirm the etiology ofdisease

28. 8. Communicate conclusions and recommend
control measures
•Timely response
•communication usually takes two forms:
•(a) an oral briefing for local authorities
•(b) a written report
•Specific control measures should be recommended whenever it is
possible

29. 9.Implement control measures
Control the source of the pathogen
Interrupt transmission
Modify host response
Prevent recurrence
May occur at any time during the outbreak

30. Control the source of
Pathogen
Remove source of contamination
Remove persons from exposure
Inactive/neutralize the pathogen
Isolate and/or treat infected person

31. Interrupt transmission
Interrupt environmental sources
Control vector transmission
Improve personal sanitation

32. Modify host response
Immuno-prophylaxis
Chemoprophylaxis

33. Source/transmission
Investigation +
Control +++
Investigation +++
Control +
Investigation +++
Control +++
Investigation +++
Control +
Known Unknown
Known
UnknownEtiology

34. 10.Follow-up the control implementations
•should follow up if they are really implemented and what effects
•An absence of new cases for at least two incubation periods
of the infectious disease under investigation could suggest
that the outbreak is subsiding

35. 11.Prepare the written report
•Summary
•Introduction& background
•Outbreak description
•Method and results
•Discussions
•Lessons learned
•Recommendation
•appendices