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Lecture 5Introduction to surveillance

• 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

• 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

population

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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 QUALI TY CYCLETHE QUALI TY CYCLE

Effi cacy/eff ectiveness

research

QAstudies

QAstudies

HAVE WEIMPROVED?

ACTION/

IMPROVEMENT

STANDARDS

GUIDELINES

PRIORITYSETTING

HOW AREWE DOING?

IndicatorsStatistics

Administrative research

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Elements of a surveillance system

• Case definition

• Indicators

• Population under surveillance

• Cycle of surveillance

• Confidentiality

• Incentives to participation

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Elements of surveillance system:case definition

• Requirements– 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

• 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

• 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 of toxic shock syndrome

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TSS: passive surveillance

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TSS: active surveillance

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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.,– networks of family physicians– schools– worksites– volunteer sites

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Surveillance methods:volunteer providers

• Example: Worcester AIDS consortium• HIV surveillance in Worcester, MA• HIV related to drug injection a major focus• Consortium members

– drug treatment agencies– community health centers– health department clinics– county jail

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Worcester AIDS Consortium

• Voluntary HIV testing

• Standard risk assessment questionnaire

• Confidential data linkage

• Results:– differences in risk behaviour and HIV

seroprevalence between treatment and non-treatment sites

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HIV risk factor surveillance

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WAC: HIV seroprevalence among male IDUs

• Site test self-report

• Drug treatment:– therapeutic community 0% 6%– detoxification 9% 15%– outpatient 29% 24%

• Non-drug treatment – health centers 21% 22%– jail 23% 23%

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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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Mortality surveillance

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Measles surveillance

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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– death certificates– hospital discharge records– disease registries– medication records– pathologist records– MD offices

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Influenza: morbidity surveillance

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Influenza: mortality surveillance

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Influenza: laboratory surveillance

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Influenza: laboratory surveillance

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Mortality: effect of ICD revisions