17a. Surveillance 12/2 Flashcards
DEFINITIONS OF SURVEILLANCE
LANGMUIR, 1963
“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, together with dissemination to those who need to know.”
DEFINITIONS OF SURVEILLANCE
D.A. HENDERSON, 1976
“Surveillance serves as the brain and nervous system for programs to prevent and control disease.”
DEFINITIONS OF SURVEILLANCE
A Dictionary of Epidemiology, 4th ed, 2001 (J.M. Last (ed))
“Systematic ongoing collection, collation, and analysis of data and the timely dissemination of information to those who need to know so that the action can be taken”
DEFINITIONS OF SURVEILLANCE KEY ELEMENTS (Detels, 1989)
Collection of health data expressly for use in health planning, disease control/ prevention, and/or health promotion Ongoing collection of data Timely analysis Easily understood Dissemination of results Action based on results Periodic evaluation of the system
USES OF SURVEILLANCE SYSTEMS (1)
To monitor changes or trends in health factors:
Prevalence/incidence of disease and/or risk factors
Emerging diseases
Geographic distribution
Risk group distribution
USES OF SURVEILLANCE SYSTEMS (2)
detect outbreaks/early warning systems Human disease Zoonotic diseases; e.g., SARS, H5N1 Food safety Drug-resistant organisms (e.g., MDR-TB)
USES OF SURVEILLANCE SYSTEMS (3)
To provide health information that can be used to design rational intervention programs
To evaluate the effectiveness of intervention strategies (e.g., vaccines, health education/behavioral programs, legislation)
Surveillance vs. screening
Data collection to measure magnitude, changes, and trends in populations
The objective is intervention in defined populations
Screening vs. surviellance
Testing to identify individuals with infection or disease
Objective is either:
Personal intervention
Protection of the public (e.g., blood donors)
Measurement of prevalence in screened populations
REQUIREMENTS FOR SURVEILLANCE
Diagnostic algorithm Staff members Sampling frame Access/network Competent laboratory
SURVEILLANCE SYSTEMS
SURVEILLANCE VS. FINDING THE RESERVOIR
For surveillance, want a representative sample
For finding the reservoir, want to find infected individuals
SURVEILLANCE SYSTEMS
DEFINING A CASE
Quickly and easily defined Selecting the right test or definition Easy, specific Clinical versus epidemiological diagnostic criteria Function over precision Disease versus infection i.e., AIDS and HIV infection
SURVEILLANCE SYSTEMS
SELECTING THE POPULATION
Defining the selection criteria Human populations Zoonotic populations Gaining access to target populations NGOs/support groups Obtaining and maintaining cooperation of target population
SURVEILLANCE SYSTEMS
SELECTING THE APPROPRIATE STRATEGY
Need for cultural sensitivity
Understanding the implications and limitations of different strategies
Selecting the appropriate surveillance strategy
Analysis
Changes in prevalence of: Infection Disease Risk activities Establishment of: Trends New reservoirs New foci (groups/locations)
SURVEILLANCE SYSTEMS
OTHER CONSIDERATIONS
Timely data processing Results and action Interpretation Facilitating appropriate action based on surveillance results
SURVEILLANCE SYSTEMS
EVALUATION AND REVISIONS
Importance of ongoing evaluation
Revising the surveillance program
When and why
SURVEILLANCE SYSTEMS
ACTIVE VS. PASSIVE SURVEILLANCE
Passive = reporting Hospitals Laboratories Clinics Physicians Active = searching
SURVEILLANCE SYSTEMS
EVENT-BASED REPORTS
Global Public Health Intelligence Network:
Websites, news wires, newspapers
Health Map Project:
Mapping of outbreaks from reservoirs and monitoring of electronic sources; and
Official alerts and surveillance reports
EpiSPIDER:
Merging of relevant data from Health Map, the Data Disaster Alert Coordinator System and ProcMED mail
Regional (e.g., Mekong infectious disease reporting)
SURVEILLANCE SYSTEMS
SENTINEL GROUPS
High-risk individuals
Vulnerable individuals
Exposed individuals (e.g., health workers)
Population surrogates (e.g., antenatal women; asthmatics)
SURVEILLANCE SYSTEMS
SENTINEL GROUPS
Previous reports of high prevalence Exposure to high-risk individuals Suspected concentration of high-risk groups Susceptible/vulnerable groups Cross-border regions Commercial centers
THE MAJOR PRODUCTS OF A SENTINEL SURVEILLANCE PROGRAM
The identity and location of the core
transmitters (reservoirs)
Trends in prevalence in risk groups, the
surrogates of the general population and
geographic areas (spread)
Trends in incidence (e.g., estimated from
prevalence in the youngest age groups;
i.e., those who have the shortest
cumulative exposure interval, or
laboratory strategies – detuned ELISA)
THE MAJOR PRODUCTS OF A SENTINEL SURVEILLANCE PROGRAM (continued)
Estimates that can be used for “advocacy”
messages to recruit support and educate
the public and decision-makers
Estimates of the number, location and
characteristics of cases that can be used
to anticipate future needs to cope with
the epidemic
VALUE OF SENTINEL SURVEILLANCE (1)
Early warning of epidemic
- Incidence and prevalence in high-risk groups/areas
Identification of size and scope of epidemic
- Incidence and prevalence in high- and low-risk groups,
by time and geographic region
Short-term evaluation of control efforts
- Change in EFFECT variables (i.e., risk factors) in
high- and low-risk groups
Long-term evaluation of control efforts
- Incidence and prevalence in high- and low-risk groups
Stimulate political and social action
VALUE OF SENTINEL SURVEILLANCE (2)
Early warning of HIV epidemic
- HIV incidence/prevalence in high-risk
groups
VALUE OF SENTINEL SURVEILLANCE (3)
Identification of size and scope of HIV epidemic
- HIV prevalence in high- and low-risk
groups, by time and geographic
region
VALUE OF SENTINEL SURVEILLANCE (4)
Short-term evaluation of HIV/AIDS control efforts
- Change in prevalence
- Change in EFFECT variables (i.e., risk
factors) in high- and low-risk groups
VALUE OF SENTINEL SURVEILLANCE (5)
Long-term evaluation of HIV/AIDS control efforts
- HIV incidence in high- and low-risk
groups
VALUE OF SENTINEL SURVEILLANCE (6)
Stimulate political and social action
EVALUATION OF A SURVEILLANCE SYSTEM
Sensitivity Timeliness Representativeness Predictive value positive Acceptability Flexibility Simplicity Cost/benefit Dissemination of results Appropriate action taken
EVALUATION OF A SURVEILLANCE SYSTEM
SENSITIVITY
What proportion of “cases” are identified?
Does the system give an accurate picture of trends and magnitudes?
EVALUATION OF A SURVEILLANCE SYSTEM
TIMELINESS
Is information disseminated rapidly enough to permit timely action based on the surveillance system?
EVALUATION OF A SURVEILLANCE SYSTEM
REPRESENTATIVENESS
Do reported cases differ
from unreported cases?
EVALUATION OF A SURVEILLANCE SYSTEM
PREDICTIVE VALUE POSITIVE
What proportion of those identified actually have the disease or factor?
EVALUATION OF A SURVEILLANCE SYSTEM
ACCEPTABILITY
Does the system stimulate the cooperation of respondents?
Does the process discourage participation?
EVALUATION OF A SURVEILLANCE SYSTEM
FLEXIBILITY
Can changes be easily made in the system to reflect changes in trends, magnitude, and other relevant factors?
EVALUATION OF A SURVEILLANCE SYSTEM
SIMPLICITY
Can the system be simplified and still obtain the necessary information?
EVALUATION OF A SURVEILLANCE SYSTEM
COST/BENEFIT
Is the system worth the cost?
Can costs be reduced without sacrificing the essential quality of the system (e.g., each 12 vs each 6 months)?
EVALUATION OF A SURVEILLANCE SYSTEM
DISSEMINATION OF RESULTS
To decision-makers
To data collectors
To the general public
EVALUATION OF A SURVEILLANCE SYSTEM
APPROPRIATE ACTION TAKEN
Are appropriate actions taken in response to the surveillance data?
Does surveillance lead to effective intervention?
DISSEMINATION
Decision-makers
Staff (motivation)
Public
