Surveillance in Public Health

Definition of Surveillance

  • Continuous and systematic collection of health-related data.
  • Essential for planning, implementation, and evaluation of public health practice (WHO, CDC).
  • Sentinel Surveillance: Involves a small group of health workers gathering data, can also include random testing in communities.

Types of Surveillance

  1. Communicable Diseases: e.g., Tuberculosis, HIV.
  2. Emerging Infectious Diseases: e.g., SARS, Ebola.
  3. Chronic Diseases: e.g., diabetes, heart disease.
  4. Preventable Diseases: e.g., Measles, pertussis.
  5. Foodborne Illnesses: e.g., Salmonella.
  6. Occupational Illnesses: e.g., black lung disease.
  7. Environmental Illnesses: e.g., lead poisoning.

Case Definitions

  • Need to objectively define if a patient has a disease.
  • Considerations:
    • Symptoms (non-specific/asymptomatic)
    • Biomarkers (cross-reactivity)
    • Observation of the agent.
    • Sequencing (costly & not all diseases are genetic).
  • Validity and reliability are crucial for definitions.

Sensitivity and Specificity

  • Sensitivity: True Positive rate; the ability to identify those with the disease.
  • Specificity: True Negative rate; the ability to identify those without the disease.
  • Objective is to balance sensitivity and specificity to minimize false positives and negatives.

Examples in Practice

  • Influenza & COVID-19: Definitions can differ and may require iterations based on the testing methods and contact definitions (close vs casual).
  • Central Line-Associated Bloodstream Infection (CLAB): Defined by specific criteria related to blood cultures and timing of infections.
  • Malaria: Symptoms must be present and confirmed with positive blood smear for diagnosis.

Errors and Biases in Surveillance

  • Variations in measurement, definitions, and populations can lead to errors.
  • Biases can be intentional or unintentional; therefore, caution is needed in data interpretation.

Public Health Applications

  • Surveillance helps in understanding disease severity, tracking public health interventions, and determining outbreak responses.
  • Data can be collected passively (ongoing report) or actively (targeted during outbreaks).

Summary

  • Accurate public health surveillance is vital for improving population health via informed decision-making.
  • Implementations depend on meticulous definitions and consideration of biases/errors in data.
  • Surveillance is often a legally mandated process to ensure community health and safety.