Descriptive Epidemiology Lecture
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Questions and Answers

Which term describes diseases that occur predictably with only minor variations?

  • Point epidemic
  • Endemic (correct)
  • Sporadic
  • Propagating epidemic

What is characterized by diseases occurring in clear excess over a period of time before returning to normal?

  • Point epidemic (correct)
  • Sporadic
  • Endemic
  • Propagating epidemic

How can ecological studies be best described?

  • They provide exhaustive individual-level data.
  • They are mainly concerned with individual case studies.
  • They focus solely on experimental methods.
  • They often lack complete data on contributing factors. (correct)

What does the ecological fallacy imply?

<p>An observed relationship in aggregate data may not apply to individuals. (A)</p> Signup and view all the answers

What type of epidemic occurs with continuing increases over time?

<p>Propagating epidemic (B)</p> Signup and view all the answers

Which of the following best describes an ecological study?

<p>A study that observes aggregate-level variables. (D)</p> Signup and view all the answers

Which study exemplifies an ecological fallacy in relation to cholera and altitude?

<p>Farr's study linking elevation to cholera mortality. (A)</p> Signup and view all the answers

Which type of disease pattern can be described as occurring rarely and without regularity?

<p>Sporadic (B)</p> Signup and view all the answers

What primarily defines place variables in epidemiology?

<p>Characteristics of geographic and environmental contexts (D)</p> Signup and view all the answers

What are urban diseases primarily associated with in the United States?

<p>Person-to-person contact and inner-city poverty (A)</p> Signup and view all the answers

Which disease illustrates variations in incidence on an international scale?

<p>Polio (D)</p> Signup and view all the answers

What influences regional differences in disease frequency within a country?

<p>Geographic climate and environmental pollution (B)</p> Signup and view all the answers

Which of these best describes localized patterns of disease?

<p>Diseases linked to specific environmental conditions in particular areas (A)</p> Signup and view all the answers

What environmental hazard are farm workers in rural areas often exposed to?

<p>Toxic pesticides and farm equipment injuries (C)</p> Signup and view all the answers

Which factor is least likely to contribute to the differences in morbidity between urban and rural areas?

<p>Universal healthcare access (C)</p> Signup and view all the answers

What is an example of a disease vector mentioned in the context of localized disease patterns?

<p>Mosquito species that spread dengue fever (B)</p> Signup and view all the answers

What term describes gradual changes in the frequency of diseases over long time periods?

<p>Secular Trends (A)</p> Signup and view all the answers

Which type of trend refers to the recurring increases and decreases in disease frequency over time?

<p>Cyclic Trend (C)</p> Signup and view all the answers

What illustrates the distribution of cases over time in an epidemic?

<p>Epidemic Curve (A)</p> Signup and view all the answers

Point epidemics typically indicate a response to which of the following?

<p>A common source of infection that groups were exposed to simultaneously (D)</p> Signup and view all the answers

What parameter does time variables NOT include when analyzing disease occurrence?

<p>Demographic factors (B)</p> Signup and view all the answers

How can enterovirus infections be characterized in terms of their frequency?

<p>They have shown increased frequency during summer months in recent decades. (B)</p> Signup and view all the answers

What has been notably unchanged over a seven-year period regarding hypertension prevalence?

<p>The overall prevalence among all adults (B)</p> Signup and view all the answers

What is typically represented on the Y axis of an epidemic curve?

<p>Number or percentage of cases that occurred (D)</p> Signup and view all the answers

Flashcards

Place variables in Epidemiology

Characteristics of a location (e.g., geographic boundaries, environment) affecting health.

Ecological Fallacy

Error of assuming that a correlation between aggregate-level data and an individual characteristic directly reflects a correlation within individuals.

Aggregate-level data

Data collected from groups of individuals (e.g., city-level disease rates).

International variations in disease

Differences in disease frequency between countries, often due to differing factors like healthcare access or environment.

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Urban vs. Rural Health Differences

Variations in health outcomes between urban and rural areas due to environmental factors (e.g., pollution), lifestyle, and poverty.

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Localized patterns of disease

Disease patterns associated with specific, local environmental conditions.

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Disease vector

An intermediary organism (e.g., insect, animal) that transmits disease.

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Polio

Infectious disease showing international variations in incidence, with decreasing worldwide prevalence.

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Secular Trend

A gradual change in disease frequency over a long period of time.

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Cyclic (Seasonal) Trend

Recurring increases and decreases in disease frequency within a year or over several years.

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Point Epidemic

A sudden outbreak of disease in a specific location around the same time, often due to a common exposure.

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What is an example of a point epidemic?

The Vibrio infections outbreak following Hurricane Katrina in 2005 is an example of a point epidemic.

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Epidemic Curve

A visual representation of disease cases over time, showing patterns of outbreaks.

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What does an epidemic curve reveal?

An epidemic curve reveals the induction period of a disease and how it spreads over time.

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Time Variable in Epidemiology

Factors related to time, such as time since exposure, calendar time, and seasonality, affecting disease occurrence.

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What are three examples of time variables?

Secular trends, cyclic trends, and point epidemics are examples of time variables.

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Sporadic Pattern

Disease occurs rarely and unpredictably, with no regular pattern.

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Endemic Pattern

Disease occurs consistently in a population at a predictable level.

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Propagating Epidemic

Disease outbreak with increasing cases over time, spreading throughout the population.

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Ecological Studies

Epidemiologic studies based on aggregate-level variables (group data, not individual data) to understand health patterns.

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Aggregate-level Variables

Data that describes characteristics of groups of individuals, like population density or average income.

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Farr's Faux Pas

Study showing a correlation between cholera and altitude in London, incorrectly attributing the cause to altitude rather than contaminated water.

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Study Notes

Descriptive Epidemiology

  • This lecture is on descriptive epidemiology, covering the topics of place, time, and ecological correlations.
  • Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems.

Lecture Objectives

  • Identify epidemiological variables (place, time)
  • Discuss ecological correlations about aggregate-level data
  • Explain the ecological fallacy

Place Variables

  • Place variables refer to the locale where people live, work, and visit.
  • They include geographic boundaries (street, city, state, region, country).
  • Place characteristics may also include environmental factors (rural/urban, domestic/foreign, institutional/noninstitutional).
  • Place variables are crucial for understanding the distribution of disease.

International and National Variations

  • International: Infectious diseases like polio show international variations in incidence and occurrence.
  • Within-country variations: Large countries with in-country variations in disease frequency.
  • Environmental factors within a country affect disease prevalence and incidence (climate, latitude, pollution).

Urban-Rural Differences

  • Urban and rural areas show variations in morbidity and mortality related to the environment and lifestyle.
  • Urban areas have a higher likelihood of diseases spread by person-to-person contact, overcrowding, and inner-city poverty, or linked to urban pollution.
  • Agriculture is a primary occupation in rural areas, with farm workers facing hazards like toxic pesticides and injuries from farm equipment.

Localized Patterns of Disease

  • Localized disease patterns are specific to environmental conditions in a geographic area.
  • Examples include cancer associated with radon gas, arsenic poisoning from water, or the presence of disease vectors.
  • A localized dengue outbreak in Texas/Mexico demonstrated a mosquito vector that is specific to the geographic area.

Place Variables: Illustration

  • An illustration includes data about age-adjusted breast cancer mortality in different countries between 1958-1959.
  • This shows variability between different countries in mortality rates.

Example 1: Victorian Water Pipes

  • This demonstrates interconnected water pipes within a city.
  • Pipes of different companies were interconnected (not regulated), increasing the risk of contamination from poor hygiene.

Time Variables

  • Time variables examine disease occurrences in relation to time since exposure, calendar time, and seasonality.
  • Examples are secular trends, cyclic (seasonal) trends, and point epidemics.
  • Secular trends are gradual changes in disease frequency over long time periods.
  • Hypertension is an example. While effective treatments exist, about one-third of the U.S. population still has hypertension.
  • Comparisons by gender, age, or race/ethnicity showed no remarkable secular change in prevalence in the seven-year period tracked.
  • Cyclic trends involve increases or decreases in disease frequency during a year or several years.
  • Pneumonia and influenza mortality peaks in February and decreases in March/April before reaching a lowest level during the early summer.
  • Enteroviruses show increasing detection during summer months in recent decades.

Point Epidemics

  • A point epidemic indicates a common source of infection, contamination, or exposure affecting a group of people simultaneously.
  • An example was the Vibrio outbreak following Hurricane Katrina in 2005.

Epidemic Curves

  • Epidemic curves visually display the distribution of illness cases over time.
  • They help identify various temporal patterns, including sporadic occurrences, consistent patterns (endemic), sudden outbreaks (point epidemic), and spreading outbreaks (propagating).

Ecological Studies

  • Epidemiological studies based on aggregate-level variables are known as ecological studies.
  • These data are often incomplete as they don't show the detailed factors contributing to disease occurrence.
  • Ecological studies tend towards descriptive analyses due to this data limitation

Ecological Fallacy

  • The ecological fallacy (aggregation bias) assumes that an association found at a group (aggregate) level is also true for individual cases.
  • This can be viewed as a form of confounding.

Illustrative Example: Dietary Fat and Cardiovascular Disease (Ecological Correlation)

  • This example demonstrates an ecological correlation between dietary fat intake and cardiovascular deaths in several countries.
  • The graph displays data for cardiovascular deaths per 1000, in relation to percentage of calories from fat, by different countries.

Illustrative Example: William Farr's Study on Cholera and Geographic Altitude

  • William Farr's 1852 study examined cholera and geographic altitude in 19th-century London.
  • While he studied higher correlation between cholera and altitude as a factor, he failed to note several other contributing factors.
  • He misinterpreted the data.

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Description

This lecture on descriptive epidemiology focuses on key concepts such as place, time, and ecological correlations. It aims to equip students with the ability to identify epidemiological variables and understand the implications of ecological correlations in health data analysis.

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