Foundations of Epidemiology Lecture 7: Measures Continued

Key Concepts: Case Definitions

ICD Codes:

• ICD: International Classification of Diseases

  • Historical Context: Initiated in 1893 by Jacques Bertillion in France, adopted in the U.S. in 1898 as ICD-1, and is now coordinated by the World Health Organization (WHO) for global health reporting.

  • Updates: Regular revisions reflect advancements in medical knowledge and practices, with the current version being ICD-11, which includes new categories such as digital health and emerging health threats.

Detailed Overview of ICD Codes

• Uses:

  • Diagnosing Health Conditions: ICD codes are fundamental for the accurate diagnosis and treatment of diseases.

  • Reporting Healthcare Information: Healthcare providers use these codes for billing and tracking patient outcomes, which informs health policy and resource allocation.

  • Revision and Data Collection: Adapted to capture new diseases, prevalence, and the effectiveness of treatment modalities.

Example ICD Codes and Importance

• Examples of ICD Codes:

  • W61.62: Struck by duck, highlighting how specific and unusual injury codes can provide insights into unusual health trends.

  • V91.07XD: Burn due to water-skis on fire, illustrating how ICD-10’s unique codes allow for a nuanced understanding of diverse causes and diagnoses.

Basic Public Health Statistics

Definitions

• Incidence: Defines the number of new cases among at-risk populations, critical for tracking disease outbreaks.

• Prevalence: Indicates existing cases of a disease at a given time, providing a snapshot of the disease burden in the community.

Rates Calculation Example

• HIV Incidence Rate Example:

  • In 2015, the HIV incidence rate in the population was reported at 23.0 new cases per 100,000 population, crucial for assessing the effectiveness of public health interventions.

  • Prevalence Example in 2022: 0.91%, indicating the ongoing burden of HIV within the community and informing resource allocation for healthcare services.

Relationship Between Incidence & Prevalence

• Cumulative Incidence:

  • Indicates the probability of developing a disease over a specified time period, allowing for more informed public health strategies.

• Prevalence:

  • Reflects the probability that any individual in the population has the disease at a specific point in time, emphasizing the ongoing impact of the disease on public health.

  • Mathematical Note: Prevalence (P) = Incidence (I) x Duration (D), illustrating the relationship between these key epidemiological measures.

Mortality Metrics Explained

• Mortality Rate:

  • A measure of the deaths occurring among a population within a given timeframe and is vital for assessing the impact of diseases on a population.

• Cumulative Mortality:

  • Similar to cumulative incidence but refers to the risk of death within a specific timeframe, essential for planning healthcare resources.

• Case-Fatality Rate:

  • The proportion of diagnosed individuals who die from the disease within a specified timeframe, crucial for evaluating disease severity and treatment effectiveness.

Years of Potential Life Lost (YPLL)

• YPLL measures the economic impact of mortality on society by quantifying the years lost due to premature death, helping policymakers prioritize health initiatives.

  • Calculation: Subtract the age at death from an index age (often 75 years).

  • Example:

    • A 25-year-old man has a YPLL of 50, indicating significant societal loss due to premature death.

    • A 70-year-old man has a YPLL of 5, emphasizing the impact of aging on life expectancy.

Disability-Adjusted Life Years (DALYs)

• Purpose: DALYs provide a comprehensive measure of overall disease burden by combining:

  • Years of Life Lost (YLL): Due to premature death.

  • Years Lived with Disability (YLD): Accounting for the severity and duration of those disabilities.

  • Significance: 1 DALY corresponds to 1 lost year of healthy life, thus informing health interventions and priorities.

Epidemiologic Transition

• Refers to the observed shift from predominance of infectious diseases to chronic diseases as life expectancy increases, which affects health policy and community health strategies.

  • Example Statistics: Comparison from 1990 to 2020 reveals significant changes in the prevalence of communicable versus noncommunicable diseases, changing healthcare resource allocation requirements.

Final Notes on Measures of Mortality & Prognosis

• Covered:

  • Mortality rates, case fatality rates, Years of Potential Life Lost, and Disability-Adjusted Life Years (DALYs).

Upcoming Topics:

• Life-tables for survival analysis,

• Understanding survival curves,

• Exploring median survival rates in various diseases and their implications for public health.

Key Questions for Understanding

• Which measure indicates the probability of contracting a disease over a specified period?(Cumulative incidence)

• How is incidence rate represented in a population or area: Point prevalence, Period prevalence, Cumulative incidence, or Incidence rate?(Incidence rate)

Key Takeaways

• Differentiation between cumulative incidence and incidence rates is essential for understanding risk and public health messaging.

• The importance of ICD coding in public health for interpreting disease burden and mortality statistics is crucial for effective health communication and resource allocation.

• A solid understanding of statistics related to public health interventions can significantly aid in effective policymaking and public health planning.