Video Summary - Introduction to Public Health Surveillance

Main ideas, concepts, and lessons

Public health surveillance is core to public health practice

Surveillance is described as one of the most important functions of the public health system.
It drives decisions and directs actions by identifying potential threats early (analogous to the “dog in the night,” i.e., alerting practitioners to danger).

Purpose and goal

The goal of public health surveillance is to provide information that can be used for public health action.
The key outcome is action; without follow-up, surveillance data “serves no real purpose.”

Public health problem-solving approach (4 steps)

What is the problem?
- Identify health problems by monitoring health events/behaviors in the population via surveillance.
What is the cause?
- Use epidemiology to identify risk factors, including:
  - environmental factors
  - behavioral factors
  - susceptibility differences
What intervention works?
- Determine what has worked for similar problems and whether it makes sense for the affected population.
How can the intervention be implemented?
- Evaluate feasibility given available resources and knowledge of the affected population.

Surveillance definition (and how surveillance differs from research data)

Surveillance is defined as the ongoing, systematic collection, analysis, and interpretation of health-related data needed for planning, implementation, and evaluation of public health practice, with timely dissemination to those responsible for prevention/control.

Key distinguishing characteristics

Systematic
- Uses standardized methods/definitions.
- Includes assessing completeness, equality, and timeliness.
Ongoing
- Continues beyond individual studies.
- Not necessarily continuous in real time, but it is not limited to a single study period.
Collection
- Decides what/how/from whom data are collected.
Analysis
- Surveillance analysis is ongoing.
- Research analysis typically occurs after data collection ends.
Also includes interpretation, dissemination, and linkage to practice.

Uses/roles of surveillance

Surveillance informing action can include:

Contact tracing and treatment (e.g., sexually transmitted diseases)
Prophylaxis for exposures (e.g., antibiotics or immunoglobulin depending on the condition)

Surveillance also functions as an alarm system:

Identify the magnitude and scope of outbreaks
Target specific groups for intervention
Track spread of emerging infections (e.g., West Nile)
Monitor changes such as antimicrobial resistance

Surveillance supports:

Program effectiveness assessment
Hypothesis generation and stimulation of research

Knowledge-check themes

Surveillance can measure trends, estimate magnitude, monitor changes in agents/environment, and assess intervention effectiveness—i.e., “all of the above.”

Legal basis in the United States

Authority for public health (including surveillance) is described as primarily state-based.
The federal role exists when disease issues impact:
- interstate commerce (commerce clause), or
- the general welfare of the nation.

State notifiable disease/reporting systems

Mandated by state law (in some states) or delegated to the State Health Officer.
Specify:
- list of reportable diseases/conditions
- who must report
- how to report
- when to report
Common reporters include:
- physicians
- laboratories
- hospitals/clinics
- sometimes school nurses/educators

Typical flow

Local health department receives report
Verifies it meets the case definition
Sends report to state
State may assist with investigations/control, especially across jurisdictions

Types of surveillance

Passive surveillance

Most routine notifiable disease surveillance.
Providers/reporters send reports following state lists of reportable conditions.
Strengths/limits:
- Simple and inexpensive
- Limited by variability in reporting quality/completeness

Active surveillance

Health agency proactively contacts/does outreach to stimulate reporting.
Can:
- validate representativeness of passive systems
- improve completeness
- support focused investigations
Often time-limited for outbreaks or special interests (e.g., SARS).
More intensive versions may include staff reviewing records (e.g., emergency rooms).

Sentinel surveillance

A subset of reporting sites (“sentinels”) report more detailed information/specimens routinely.
Examples mentioned:
- Chickens in woods for arboviruses (e.g., periodic blood collection to detect infection)
- Cotton pledgets in sewers sampled/tested for enteric pathogens

Syndromic surveillance

Focuses on signs/symptoms rather than lab-confirmed, physician-diagnosed diseases.
Case definitions are less specific → follow-up is always needed to confirm whether an outbreak is real.
Advantages:
- faster reporting (doesn’t wait for diagnosis)
- useful as an early warning system for bioterrorism
Examples/expanded “loose” uses mentioned:
- school/work absenteeism
- 911 calls
- over-the-counter medication sales (e.g., rise in antidiarrheal sales during the cryptosporidiosis outbreak in Milwaukee)

Attributes of a surveillance system (evaluation criteria)

A system can be evaluated like assessing a “vehicle/home”: understand what it can and can’t do.

Attributes discussed

Usefulness
- Achieves objectives to the desired extent
Data quality
- Reliability, completeness/accuracy of fields, and need for training/support
Timeliness
- How quickly reports arrive (critical for some conditions)
Flexibility
- Ability to adapt to changes
Simplicity
- Ease of operation
- Example: too many fields can cause data entry delays; simpler design improves usability
Stability
- Reliable functioning; not frequently breaking down
Sensitivity
- Captures intended cases (e.g., 10% vs 80%)
Positive predictive value (PPV)
- How many reported cases truly meet the case definition
Representativeness
- Captures events across the target population, not just certain groups
- Example: STI surveillance often underrepresents parts of the population
Acceptability
- Willingness of users to participate and report

Tradeoff

Sensitivity vs PPV often have an inverse relationship (increasing sensitivity can reduce PPV), so design depends on goals.

Methodology / process: Public health surveillance process (detailed steps)

At least five steps are emphasized:

Data collection
- Decide system goal and specific objectives.
- Determine:
  - what to monitor
  - what data will be collected
  - definitions and data fields
  - why each data element is collected and how it will be used
- Decide:
  - who collects data and how
  - target population and setting
  - active vs passive structure
  - transmission method (paper/mail/electronic) and timing
- Consider common surveillance data sources (examples mentioned):
  - administrative/billing systems
  - laboratory surveillance (e.g., PulseNet)
  - environmental/vector/animal surveillance
  - syndromic indicators (e.g., 911 calls, absenteeism, retail medication sales—mentioned earlier)
  - laws/policy information and other relevant systems
Data analysis
- Decide:
  - who analyzes data
  - analytic methods (from simple graphs to stratified analysis and confidence intervals)
  - analysis frequency (daily/weekly/monthly depending on purpose)
- Examples given:
  - time-based outbreak curves (West Nile example by week)
  - mapping patterns (laboratory-confirmed cases as dots; clustering)
  - analysis by person (demographics/risk patterns; West Nile hospitalization rates by age/sex)
Interpretation
- Link results to person, place, and time (the “epi triad”).
- If case counts rise, explore potential explanations such as:
  - increased healthcare access
  - changed reporting procedures/surveillance system
  - changed case definitions
  - increased laboratory testing
  - increased provider awareness (“higher index of suspicion”)
Dissemination
- Plan distribution to stakeholders who need it:
  - newsletters/bulletins/alerts
  - annual summaries/reports
  - journal articles
  - press releases
  - social media
- Target audiences mentioned:
  - public health practitioners
  - clinicians/health care providers
  - policymakers/decision makers
  - community organizations
  - the general public
- Knowledge-check: newspaper articles are generally not a good data source for surveillance (with limited exceptions).
Follow-up action (link to action)
- Surveillance must lead to action.
- Provides the bridge from “information” to “control.”
- Pertussis example:
  - case decline with vaccination, followed by later resurgence (1980–2000)
  - findings implicated adult/child exposure through adults
  - led to changing immunization recommendations to include adult boosters to prevent spread to young children

Surveillance-based action: what surveillance findings are used to do (action categories)

Describe the burden (or potential burden) of disease
Monitor trends/patterns
Look at risk factors and agents
Detect sudden changes in occurrence/distribution
Provide data for programs, policies, and priorities
Evaluate prevention/control efforts

Speakers / sources featured

Ralph Cordell — epidemiologist at the Centers for Disease Control and Prevention (CDC), Atlanta
CDC (Centers for Disease Control and Prevention) — referenced as an organization; later notes CEU webinar details
CSTE (Council of State and Territorial Epidemiologists) — co-developer of the national notifiable disease list with CDC
US Constitution / Bill of Rights (Article 12 context) — used to explain legal authority framework
World Health Organization (WHO) — referenced for international coordination and examples of internationally reportable conditions
Bill Fahy — quoted (former CDC director involved in global smallpox eradication)
PulseNet — referenced as an example of laboratory surveillance
MMWR (Morbidity and Mortality Weekly Report) — referenced as the weekly and annual publication outlet for notifiable disease data
Nationally notifiable disease reporting system framework — referenced as the national/state reporting structure (CDC + CSTE collaboration)

Introduction to Public Health Surveillance

Key takeaways