2007 johns hopkins bloomberg school of public health principles of surveillance jonathan samet, md,...
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2007 Johns Hopkins Bloomberg School of Public Health
Principles of SurveillancePrinciples of Surveillance
Jonathan Samet, MD, MSJohns Hopkins Bloomberg School of Public Health
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Learning Objectives
Define the basic terms related to surveillance
Specify characteristics of surveillance systems for different objectives
Describe selected major surveillance systems
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Uses of Morbidity and Mortality Data
1. Hypothesis generation
2. Health planning
3. Program evaluation
4. Surveillance
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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.”
— U.S. Centers for Disease Control and Prevention
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Information Loop of Public Health Surveillance
Source: adapted by CTLT from http://www.cdc.gov/epo/dphsi/phs/overview.htm
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Immediate Detection of . . .
Epidemics Established agents Emerging agents
Newly emerging health problems
Changes in health practices
Changes in antibiotic resistance
Chemical and biological terrorism
Source: Thacker and Stroup. (1994).
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Periodic Dissemination for . . .
Estimating the magnitude of the health problem, including costs
Assessing control activities
Setting research priorities
Testing hypotheses
Facilitating planning
Monitoring risk factors
Monitoring changes in health practices
Source: Thacker and Stroup. (1994).
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Source: Thacker and Stroup. (1994).
Archival Information for . . .
Describing the natural history of disease
Facilitating epidemiologic and laboratory research
Validating the use of preliminary data
Setting research priorities
Documenting distribution and spread
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Langmuir on Surveillance
“Surveillance, when applied to a disease, means the continued watchfulness over the distribution and trends of incidence through the systematic collection, consolidation, and evaluation of morbidity and mortality reports and other relevant data.”
— Alexander Langmuir
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From Vector to Agent to Disease: Surveillance Points
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Points for Surveillance Example: Tobacco
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Modeling a Surveillance System
Source: Teutsch and Churchill. (2000).
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Surveillance Systems: Some Characteristics
Geographic scale: local to global
Event identification: active or passive
Scope: all or sentinel events
Focus on monitoring: vector agent outcome
Purpose: tracking or alarm
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Modeling a Surveillance System
Source: Teutsch and Churchill. (2000).
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Occurrence of an Event: Kind of Event
What kind of an event? Exposure
Exposure to air pollution, bio-monitoring Disease
Communicable diseases, chronic diseases, syndromes
Injuries Motor vehicle accidents, homicide
Health risk factors Obesity
Health behaviors Smoking, sexual behavior, substance use
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What do you want to do a surveillance of? Exposure
Agents Biomarkers
Exposure determinants Behaviors Risk factors Vectors Host characteristics Reservoirs
Health outcomes Disease Death Medical care
Occurrence of an Event: Surveillance of What?
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WHO Global Tobacco Surveillance
World Health Survey Household survey of adults (18+) conducted in
70 countries in 2002–2003
STEPwise Approach to Surveillance (STEPS) Modular survey of chronic disease risk factors
Global Youth Tobacco Survey School-based survey Global Adult Tobacco Survey (planned)
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Occurrence of an Event: What Type of System?
What type of system would work best? Universal: population tracking
Choose entire population or a representative sample to monitor for condition of interest (measles, obesity, bioterrorism agents)
Sentinel: “warning” signs Choose key “location” to monitor for
condition of interest (e.g., unusual disease)
“Locations” might include sites, events, providers, animals, vectors
Choose a “location” that is most susceptible to change
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Capturing an Event: Approaches
Active Periodic solicitation of case reports from
reporting sources, such as physicians, hospitals, laboratories, etc.
Passive Relies on health care providers to report on
their own initiative Must make this reporting process simple and
time efficient
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Active Advantages
Can be very sensitive
Can collect more detailed information
May be more representative
Disadvantages Costly Labor intensive Difficult to
sustain over time
Active vs. Passive: Advantages and Disadvantages
Passive Advantages
Less costly Eager to design
and carry out Useful for
monitoring trends over time
Disadvantages Low sensitivity Amount of data
available is limited
May not be representative
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Active: SEER Cancer Registry
Source: http://seer.cancer.gov
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Passive: CDC Notifiable Diseases
Provisional Cases of Selected Notifiable Diseases, United States,Week Ending July 16, 2005*
Source: U.S. Centers for Disease Control. (2005).
* Incidence data for reporting year 2005 is provisional
Reporting AreaAIDS Chlamydia
Cum. 2005
Cum. 2004
Cum. 2005
Cum. 2004
South Atlantic 6,473 6,022 90,687 91,830
Delaware 100 80 1,729 1,514
Maryland 812 686 9,692 10,009
District of Columbia
467 355 1,970 1,910
Virginia 307 329 10,550 11,732
West Virginia 36 30 1,350 1,493
North Carolina 531 333 17,485 15,198
South Carolina 386 374 10,433 9,891
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Modeling a Surveillance System
Source: Teutsch and Churchill. (2000).
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Processing and Analyzing the Event
How do you detect a signal?
Data capture/editing/management
Analytical approaches
Statistical approaches
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Examine the Event by Person, Place, and Time
By person: demographics, lifestyle, risk factors
By place: GIS mapping
By time: epidemic curve, time series analysis
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By Place: GIS Mapping
GIS: geographic information systems GIS links location to information (such as
people to addresses, buildings to parcels, or streets within a network) and layers that information to give you a better understanding of how it all interrelates
You choose what layers to combine based on your purpose
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Image source: adapted by CTLT from U.S. Centers for Disease Control and Prevention. (2005).
By Time: Time Series
Time series analysis accounts for the fact that data points taken over time may have an internal structure (such as trend or seasonal variation) that should be accounted for
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By Person: Demographics
Age
Race/ethnicity
Occupation
Socioeconomic status
Sex
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By Place
Small areas
Governmental units
Nations
Unit chosen to examine is determined by the availability of data on particular geographic scales
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Source: U.S. National Cancer Institute. (1999).
Cancer Mortality Rates, by State
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Heart Disease Death Rates: 1991–1995
Source: U.S. Centers for Disease Control and Prevention.
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Male Lung Cancer Incidence Rate per 100,000
Source: adapted by CTLT from GLOBOCAN. (2002). IARC.
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Female Lung Cancer Incidence Rate per 100,000
Source: adapted by CTLT from GLOBOCAN. (2002). IARC.
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Modeling a Surveillance System
Source: Teutsch and Churchill. (2000).
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Disseminating the Information
Process information for your audience Broadcast faxes, email, mailings to
dissemination lists Locally, to clinicians Regionally, to health departments
Web sites Journal articles Media
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Tobacco Use Information Systems
Global InfoBase Data repository for
chronic disease risk factor prevalence, including tobacco use
Summarized in Surveillance of Risk Factors Report (SuRF)
Global Information System on Tobacco Control (GISTOC) Provides links to
tobacco-related databases
Image source: World Health Organization. (2003 and 2005).
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World Health Organization: The SuRF Report
Source: The World Health Organization.
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Modeling a Surveillance System
Source: Teutsch and Churchill. (2000).
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Model for State-Based Chronic Disease Surveillance
Response
Hypothesis generation
Health planning
Program evaluation
Source: Remington and Goodman. (1999).
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Summary
Surveillance takeaways Ongoing collection Systematic according to a plan Results given to those who need to know them Resulting action is based in evidence gained
in the surveillance system
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