Transcript Syndromic surveillance

Introduction to
Surveillance
Public Health Surveillance
Ongoing, systematic collection, analysis,
and interpretation of health-related data
essential to the planning, implementation,
and evaluation of public health practice,
closely integrated with the timely
dissemination of these data to those
responsible for prevention and control
Public Health Surveillance
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Systematic
Ongoing
Collection
Analysis
Interpretation
Dissemination
Of Health data
Link to public health practice
Purposes of Public Health Surveillance
To portray the ongoing pattern of
health-related states and events, to…
 Assess public health status
 Trigger public health action
 Define public health priorities
 Evaluate programs
Some Uses of Public Health Surveillance
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Detect sudden changes in disease
occurrence and distribution
Monitor trends and patterns
Portray the natural history of a disease
Generate hypotheses, stimulate research
Monitor changes in infectious agents
Detect changes in health practices
Evaluate control measures
Facilitate planning
Process of Public Health Surveillance
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Data collection
Data tabulation
Data analysis
Data interpretation
Data dissemination
Link to action
Data Sources/Methods
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Notifiable diseases
Laboratory specimens
Vital records
Sentinel surveillance
Registries
Surveys
Administrative data systems
Other data sources
Types of Surveillance
Passive: Provider initiated
Active: Health-agency solicited
Sentinel Surveillance
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Reporting of health events by health
professionals who are selected to
represent a geographic area or a
specific reporting group
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Can be active or passive surveillance
Syndromic Surveillance
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Syndromic surveillance – focuses on one
or constellation of symptoms rather than
diagnosed disease
Data Tabulation
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Time
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Place
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Person
Data Analysis by Place
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Where reported (usual method)
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Where exposure occurred (preferred)
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Allows prevention resources to be
targeted effectively
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Use of computers and spatial mapping
software allows for sophisticated
analysis
Data Analysis by Person
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Demographics
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Age (most common), race, sex
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Occupation
Risk factors, if collected
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e.g., Vaccination status
Analysis of Surveillance Data
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Descriptive – most common
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Analytic methods
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Time-series analyses to detect
aberrations
Time-space clustering
Process of Public Health Surveillance
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Data collection
Data tabulation
Data analysis
Data interpretation
Data dissemination
Link to action
What can account for an
apparent increase in cases?
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Change in reporting procedures / change in
surveillance system
Change in case definition
Improvements in diagnostic procedures
Increased awareness
Increased access to health care
New physician, ICN, or clinic – may see more
referred cases, may make diagnosis more often, or
report more consistently
Laboratory or diagnostic error
Batch reporting
Change in denominator
True increase in incidence
Dissemination of Surveillance Data
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Health agency newsletter (e.g., MMWR)
Surveillance summaries / reports
Medical / epidemiologic journal articles
Press releases
Link to Action
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Outbreak investigation
Disease control
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Vaccination / prophylaxis
Elimination of cause
Interruption of transmission
Development, targeting of programs
(education, risk reduction, etc.)
Development of policies, regulations
What is a Case Definition?
A set of uniformly applied criteria for
determining whether a person should be
identified as having a particular disease, injury,
or other health related condition.
When do we use case definitions?
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For reportable diseases
For outbreak investigations
For epidemiological studies
Case definitions may vary for a given disease depending
on the purpose for the collection of data
Why do we need case definitions?
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To accurately classify persons who are ill
To standardize who is reported for a given
disease.
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Allows comparison between different geographic
regions or time periods
Standard Case Definition Structure
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Basic symptoms
Other clinical signs determined by the disease
pathophysiology
Laboratory data
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Epidemiological criteria (not necessary)
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Benefits of Standard Case Definitions
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Surveillance system uniformity and simple
implementation
Reproducibility and reliability of diagnostics
Disease registration system stability
Reliability of notifiable case detection
Ruling out registration of diseases having similar
clinical symptoms
Provision of efficient tracking over incidence in
population
Comparison of incidence data for various
geographical areas
3-Tiered Case Definitions
Confirmed case
Probable case
Suspect case
diagnostics
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False negative
False positive
TRUTH
50
3
53
30
17
45
80
20
Sensitivity: 50/80 = 62.5%
Specificity: 17/20 = 85%
Influence of Standard
Case Definition on Sensitivity and Specificity
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Wide case definition – highly sensitive
epidemiological surveillance system
Restricted case definition– highly specific
epidemiological surveillance system
Case definition can not be wide and restricted
at the same time.
Solution – several levels of accuracy in case
definition formulation
Case Definitions: Suspect or Possible
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Includes clinical features of the disease
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Signs and symptoms frequently found
Signs and symptoms that help distinguish
from other diseases
Indicates that a specimen should be
collected and the case should be reported
May (often) trigger sample collection for
laboratory investigation
Example of Meningococcal Infection
Probable Case Definition
Probable: suspect case as above AND
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Turbidity of cerebrospinal fluid
(upon presence or absence of
Gram+ flora) OR
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Presence of outbreak and
epidemiological link with the
confirmed case
Case Definitions: Confirmed
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Final laboratory confirmation of ongoing
or recent infection
The case is then considered a confirmed
case
Summary
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Case definitions can vary in their use of clinical,
laboratory, and epidemiologic criteria to define cases
Standard case definitions are needed for uniform
reporting of infectious diseases and for comparative
analysis of epidemiological surveillance data over
time and geographic areas
Standard case definitions can vary in various
surveillance systems depending on epidemiological
surveillance objectives
Standard case definitions may be periodically
revised upon necessity to change the degree of
surveillance system sensitivity