2007 Johns Hopkins Bloomberg School of Public Health Principles of Surveillance Jonathan Samet, MD, MS Johns Hopkins Bloomberg School of Public Health

2007 Johns Hopkins Bloomberg School of Public Health

Principles of SurveillancePrinciples of Surveillance

Jonathan Samet, MD, MSJohns Hopkins Bloomberg School of Public Health

2 2007 Johns Hopkins Bloomberg School of Public Health

Learning Objectives

Define the basic terms related to surveillance

Specify characteristics of surveillance systems for different objectives

Describe selected major surveillance systems


Uses of Morbidity and Mortality Data

1. Hypothesis generation

2. Health planning

3. Program evaluation

4. Surveillance


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


Information Loop of Public Health Surveillance

Source: adapted by CTLT from http://www.cdc.gov/epo/dphsi/phs/overview.htm


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).


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




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


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


From Vector to Agent to Disease: Surveillance Points


Points for Surveillance Example: Tobacco


Modeling a Surveillance System

Source: Teutsch and Churchill. (2000).


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





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


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?


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)


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


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


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


Active: SEER Cancer Registry

Source: http://seer.cancer.gov


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





Processing and Analyzing the Event

How do you detect a signal?

Data capture/editing/management

Analytical approaches

Statistical approaches


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


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


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


By Person: Demographics

Age

Race/ethnicity

Occupation

Socioeconomic status

Sex


By Place

Small areas

Governmental units

Nations

Unit chosen to examine is determined by the availability of data on particular geographic scales


Source: U.S. National Cancer Institute. (1999).

Cancer Mortality Rates, by State


Heart Disease Death Rates: 1991–1995

Source: U.S. Centers for Disease Control and Prevention.


Male Lung Cancer Incidence Rate per 100,000

Source: adapted by CTLT from GLOBOCAN. (2002). IARC.


Female Lung Cancer Incidence Rate per 100,000

Source: adapted by CTLT from GLOBOCAN. (2002). IARC.





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


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).


World Health Organization: The SuRF Report

Source: The World Health Organization.





Model for State-Based Chronic Disease Surveillance

Response

Hypothesis generation

Health planning

Program evaluation

Source: Remington and Goodman. (1999).


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

Documents

2007 Johns Hopkins Bloomberg School of Public Health Principles of Surveillance Jonathan Samet, MD, MS Johns Hopkins Bloomberg School of Public Health