Lecture 2A Principles of epidemiology

Principles of Epidemiology

Overview

  • Descriptive Studies: Discuss patterns of disease in populations, using routinely collected data for a useful overview of health issues.

  • Aetiological Studies: Help define problems by identifying the amount of disease and pointing to localized issues (e.g., among occupational groups).

Clinical Considerations

  • Clinician impressions may misrepresent disease prevalence; population data is essential for accurate understanding.

  • Understanding the natural history of disease requires knowledge of disease progression over time.

Health Service Planning

  • Planning often utilizes historical data to forecast future service demands, supported by descriptive data.

Describing Disease Patterns

Key Aspects

  • Time: When do diseases occur? Trends can include long-term trends, periodic changes, and epidemics.

  • Place: Where are diseases more prevalent? Geographical variations can indicate localized problems or trends.

  • Personal Characteristics: Who is affected? Factors include age, gender, and social class.

Variation of Disease

Time

  • Long-term Trends: Observable changes over years, such as life expectancy variations by demographic groups.

  • Periodic Changes: Seasonality in disease incidence, periodic epidemics affecting specific populations.

Example Cases

  • Tuberculosis Trends: Historical death rates in England and Wales highlighting the impact of chemotherapy and vaccination.

  • Lung Cancer Incidence: Secular trend analysis from 1948 to 2015 in New Zealand

Health Trends in New Zealand

  • Variations in respiratory, circulatory, and infectious disease rates demonstrated across decades.

Additional Factors Affecting Disease Incidence

Cohort Effects

  • Cohort: Defined as a group sharing a common experience or exposure (e.g., birth or environmental exposures).

Personal Characteristics

  • Age: Disease frequency increases with age due to biological aging and lead times for chronic conditions.

  • Gender: Examination of disease incidence and mortality rates by gender reveals disparities in health outcomes.

Social Factors

  • Marital Status: Data shows higher suicide rates and serious health implications among divorced individuals.

  • Ethnicity: Variations in morbidity and mortality rates are influenced by cultural, dietary, environmental, and genetic factors.

Socioeconomic Factors

  • Social Deprivation: Associated with disease prevalence and health outcomes, but does not directly cause disease. Requires understanding which characteristics increase disease risk.

  • Occupation: Certain occupations have higher incidences of specific diseases, as seen in lung cancer data.

Summary Considerations

  • In epidemiology, consider important aspects for each disease: trends over time, geographical variations, and personal characteristics such as age, gender, social class, and ethnicity.