Reingold, A.L. 1998. Outbreak Investigations - A Perspective. Emerging Infectious Diseases 4: 21-27. Flashcards
Objective of paper:
To outline the general approach to conduct an
outbreak investigation.
Reasons for Investigating Outbreaks
To prevent additional cases by identifying and
eliminating the source of infection.
Results of the investigation may lead to recommendations or strategies for preventing similar
future outbreaks.
Opportunity to describe new diseases and learn more
about known diseases
Evaluate existing prevention strategies (eg. vaccines).
Teach and learn epidemiology.
Address public concern about the outbreak.
Three Types of Activities
Epidemiological investigation.
Environmental investigation.
Interaction with the public, the press, and the legal
system.
6 constraints of Epidemiological Investigation of Outbreak
1) Great urgency to find the source and
prevent additional cases when outbreak is
ONGOING.
2) Pressure to conclude investigation rapidly .
3) Limited number of cases available for study
limiting statistical power of study.
4) Early media reports may bias subsequent
interviews.
5) Legal liability may put pressure to conclude
study quickly which may lead to hasty decisions
regarding the source.
6) If detection of outbreak is delayed, it may
compromise clinical and environmental samples
10 components of outbreak investigation
1) Establish case definition
2) Confirm that cases are real
3) Establish background rate of disease
4) Define scope of outbreak
5) Examine descriptive epidemiological features of cases
6) Generate hypotheses
7) Test hypotheses
8) Collect and test environmental samples
9) Implement control measures
10) Inform the public through the press
Case Definition
Formulation of case definition and exclusion criteria
Straightforward if disease well-known
Gastroenteritis caused by Salmonella
Clinical case: diarrhea
Laboratory-confirmed case: culture of
Salmonella
Complex if disease is new and clinical range unknown
Case Confirmation
Review of cases by examination of patient or review of
medical records
Often include some laboratory evaluation
Background Rate
Should demonstrate that number of cases are in
excess of usual number
Define temporal and geographical range of outbreak
Find cases to describe epidemiological characteristics
Descriptive Epidemiology
Examination of characteristics of ill persons and
generation of HYPOTHESES to explain outbreak.
Epidemic curve may suggest point-source
(common-source) vs host-to-host transmission
Generating a Hypothesis
Source(s) and route(s) of exposure (pathogens) must be determined to understand why an outbreak occurred, to prevent similar outbreak to prevent others to be exposed
Review epidemiological, microbiological, veterinary
data
Open-ended interviews of those infected (or their
surrogates)
Testing the Hypothesis
Analytic epidemiologic study to test hypothesis
should be considered
Goal: to assess the relationship between given
exposure and the disease under study
Often, need multiple analytic studies to generate
right hypotyhesis
Need to use statistic BUT have to considerpossibility that siginificant correlation may be
fortuitous.
Need to look for causal relationship using doseresponse.
Need to pass the Koch test!
Different designs
Case-control
•Retrospective cohort
•Cross-sectional studies
Environmental Investigations
Environmental samples (food, beverages, water, coooling tower, soil, etc) may help confirming the source of the outbreak.
Epidemiological investigation should guide the
collection and testing of samples.
Samples may not represent source or maybe
mishandled, no conclusive results if negative.
Technical challenges:
Insensitive methods
Methods difficult to apply
No existing methods
Control Measures
Timely implementation of control measures to
minimize further illness and death.
Must balance responsibility to prevent further disease
and protect reputation of an institutuion.
