Transcript Lecture 10 - Surveillance

Lecture 10
Introduction to Surveillance
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Definitions of surveillance
Objectives of surveillance
Public health vs health care surveillance
Elements of a surveillance system
Surveillance methods
Cross-sectional and longitudinal approaches
Sources of bias
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Definition of surveillance
(Last, Dictionary of Epidemiology. 2001)
• Systematic ongoing collection, collation,
and analysis of data and the timely
dissemination of information to those who
need to know so that action can be taken.
• (Source: WHO)
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Definition of surveillance
(Last, Dictionary of Epidemiology. 2001)
• Ongoing systematic collection, analysis,
and interpretation of health data, essential to
the planning, implementation, and
evaluation of public health practice, closely
integrated with the timely dissemination of
these data to those who need to know.
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Definition of surveillance
(Last, Dictionary of Epidemiology. 2001)
• Continuous analysis, interpretation, and
feedback of systematically collected health
data, generally using methods distinguished
by their practicality, uniformity, and rapidity
rather than by accuracy or completeness.
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Objectives of surveillance
• Related to particular population
• Links to services
– disease control
– results lead to action (e.g., case or outbreak
investigation, contact tracing, interventions)
• Data for planning of services
– identification of high-risk groups
– projection of future service needs
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Objectives of surveillance
(cont’d)
• Data for evaluation of services
• Links to research (research is not primary
objective)
– development of hypotheses
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Types/Sources of data
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Morbidity and mortality reports
Laboratory diagnoses
Outbreak reports
Vaccine utilization
Sickness absence
Disease determinants (e.g., reservoirs of disease)
Susceptibility measures (e.g., serological
surveillance)
• And many others!
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Examples of surveillance
• Communicable diseases
• Health behaviors:
– Drug use, risky sexual behavior
– Risk factors for chronic diseases (e.g. smoking)
• Environmental risks and diseases
• Health care
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Public health vs health care
surveillance
• Public health
– protection, promotion, and restoration of health
of population
– includes health care services, especially if
publicly-funded
• Health care
– services provided to individuals or communities
by agents of health services or professionals, to
promote, maintain, monitor, or restore health.
Not limited to medical care (therapy by MD)
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Public health vs health care
surveillance (cont’d)
• Health care surveillance
– may be part of public health surveillance (e.g.,
Montreal DSP)
– also conducted by other agencies and/or health
care organizations (e.g., hospitals)
• Population may differ
– public health: usually defined geographically
(district, region, country)
– health care: recipients of services or catchment
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population
Objectives of surveillance of health care
• Related to particular population
– e.g., catchment population, patients, clients
• Monitoring of various aspects of health care
– Safety (e.g., medical errors)
– Efficiency (e.g., length of stay)
– Professional practices (e.g., adherence to
guidelines)
– Acceptability (e.g., satisfaction with services)
– Equity (e.g. access)
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Health care surveillance and
quality improvement
• Quality management/assurance programs
– system for maintaining/improving service
• Quality assessment/audit
– measurement aspects: surveillance (incl.
monitoring & surveys)
• Quality improvement
– organized efforts to apply results of
surveillance to improved services
• Linked through “Quality Cycle”
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THE QUALITY CYCLE
Efficacy/
effectiveness
research
Indicators
Statistics
PRIORITY
SETTING
HAVE WE
IMPROVED?
QA
studies
STANDARDS
QA
studies
GUIDELINES
HOW ARE
WE DOING?
ACTION/
IMPROVEMENT
Administrative
research
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Elements of a surveillance
system
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Case definition
Indicators
Population under surveillance
Cycle of surveillance
Confidentiality
Incentives to participation
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Elements of surveillance system:
case definition
• Requirements
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Indicator (not diagnostic) of trends
Simple
Feasible
Reliable
Inexpensive
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Elements of surveillance system:
case definition
• Examples
– Measles: fever with red rash, red eyes,
disappearing within a week
– Cholera: Sudden and severe watery diarrhoea,
with rapid and massive dehydration
– Malaria: Fever, rigors, headache, body aches,
inability to carry out normal daily activities
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Case definition for AIDS (US)
• Original surveillance definition:
– List of opportunistic infections or cancers
without other cause
• 1985 revision
– inclusion of positive HIV test result
– additional conditions
• 1987 revision
– more conditions (extrapulmonary TB)
• 1993 revision
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Elements of surveillance system:
population under surveillance
• Population-based
• Institution-based
– hospitals, practices, nursing homes, prisons,
schools
• Combinations
– e.g., Drug Abuse Warning Network (DAWN) in
US: morbidity and mortality data on illicit drug
use from hospital ERs and medical
examiners/coroners
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Elements of surveillance system:
cycle of surveillance
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Occurrence of health event
Detection by health care provider
Notification of health agency
Analysis and interpretation
Dissemination
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Elements of surveillance system:
confidentiality
• Legally mandated reporting requires
confidentiality precautions
– limited access to data (locks, passwords etc)
– encryption algorithms for coding names
• Perceived lack of confidentiality a major
deterrent to completeness of reporting
– STDs
– drug use
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Surveillance methods
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Active vs passive methods
Legally notifiable diseases
Sentinel events
Sentinel surveillance
Cross-sectional vs longitudinal
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Active vs passive surveillance
• Passive surveillance
– Issue case definition
– Wait for cases to be reported
• Active surveillance
– Go looking for cases
– E.g., MD offices, hospitals, pathology
departments
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Surveillance methods:
notifiable diseases
• Universally reportable:
– internationally quarantinable diseases:plague, cholera,
yellow fever, smallpox
– under WHO surveillance: e.g., influenza, malaria
• Regularly required:
– e.g., typhoid, diphtheria
• Others (vary by country, location):
– Selectively required
– Outbreaks of public health importance
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Surveillance methods:
sentinel events
• Sentinel health event:
– condition that can be used to assess the stability
or change in health levels of a population
– e.g.,
• death from acute head injury a sentinel event for
severe traffic injury
• death or severe health effect resulting from wrong
medication, route or dose is a sentinel event for
medication errors
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Surveillance methods:
Sentinel surveillance
• Surveillance based on sub-populations
(sentinel populations) selected to represent
the relevant experience of entire
population, e.g.,
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networks of family physicians
schools
worksites
volunteer sites
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Surveillance methods:
longitudinal vs cross-sectional
• Longitudinal
– Ongoing data collection
– Incident cases
– Examples: notifiable diseases, vital statistics,
disease registries
• Cross-sectional
– Serial surveys
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Surveillance methods:
surveys
• Examples:
– National Population Health Survey
– Sante Quebec
• Content:
– Conditions, behaviours not easy to monitor
routinely (mental health problems, smoking,
use of complementary/alternative therapies)
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Sources of bias in surveillance
systems
• Information bias:
– Incomplete reporting (e.g., passive vs active
surveillance)
– Differences/changes in case definition
• Selection bias:
– Non-representative sentinel populations
– Non-representative survey samples
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Checks on completeness of
reporting
• Alternative methods to identify reportable
cases
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death certificates
hospital discharge records
disease registries
medication records
pathologist records
MD offices
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