Central obesity correlates with an increased incidence of

Managerial Epidemiology

Chapter 4

Descriptive Epidemiology: Person, Place, Time

Learning Objectives

State primary objectives of descriptive epidemiology

Provide examples of descriptive studies

List characteristics of person, place, and time

Characterize the differences between descriptive and analytic epidemiology

Descriptive vs. Analytic Epidemiology

Descriptive studies--used to identify a health problem that may exist. Characterize the amount and distribution of disease

Analytic studies--follow descriptive studies, and are used to identify the cause of the health problem

2

Objectives of Descriptive Epidemiology

To evaluate and compare trends in health and disease

To provide a basis for planning, provision, and evaluation of health services

To identify problems for analytic studies (creation of hypotheses)

3

Descriptive Studies and Epidemiologic Hypotheses

Hypotheses--theories tested by gathering facts that lead to their acceptance or rejection

Three types:

Positive declaration (research hypothesis)

Negative declaration (null hypothesis)

Implicit question (e.g., to study association between infant mortality and region)

4

Mill’s Canons of Inductive Reasoning

The method of difference--all the factors in two or more places are the same except for a single factor.

The method of agreement--a single factor is common to a variety of settings. Example: air pollution.

5

Mill’s Canons (cont’d)

The method of concomitant variation--the frequency of disease varies according to the potency of a factor.

The method of residues--involves subtracting potential causal factors to determine which factor(s) has the greatest impact.

6

Method of Analogy (MacMahon and Pugh)

The mode of transmission and symptoms of a disease of unknown etiology bear a pattern similar to that of a known disease.

This information suggests similar etiologies for both diseases.

Three Approaches to Descriptive Epidemiology

Case reports--simplest category of descriptive epidemiology

Case series

Cross-sectional studies

Case Reports and Case Series

Case reports--astute clinical observations of unusual cases of disease

Example: a single occurrence of methylene chloride poisoning

Case series--a summary of the characteristics of a consecutive listing of patients from one or more major clinical

Example: five cases of hantavirus pulmonary syndrome

7

Cross-sectional Studies

Surveys of the population to estimate the prevalence of a disease or exposure

Example: National Health Interview Survey

Characteristics of Persons Covered in Chapter 4

Age

Sex

Marital Status

Race and ethnicity

Nativity and migration

Religion

Socioeconomic status

Age

One of the most important factors to consider when describing the occurrence of any disease or illness

8

Trends by Age Subgroup

Childhood to early adolescence

Leading cause of death, ages 1-14 years—unintentional injuries

Infants—mortality from developmental problems, e.g., congenital birth defects

Childhood—occurrence of infectious diseases such as meningococcal disease

Trends by Age Subgroup (cont’d)

Teenage years

Leading causes of death—unintentional injuries, homicide, and suicide

Other issues—unplanned pregnancy, tobacco use, substance abuse

Trends by Age Subgroup (cont’d)

Adults—leading causes of death

Unintentional injuries

Cancer

Heart disease

Older adults—deaths from chronic diseases (e.g., cancer and heart disease) dominate.

Elderly—deaths from chronic diseases and limitations in activities of daily living

Age Trends in Cancer Incidence

Age-specific rates of cancer incidence increase with age with apparent declines late in life.

Reasons for Age Associations

Validity of diagnoses across the life span

Multimodality of trends

Latency effects

Action of the “human biologic clock”

Life cycle and behavioral phenomena

Validity of Diagnoses

Classification errors

Age-specific incidence rates among older groups

Exact cause of death can be inaccurate due multiple sources of morbidity that affect elderly.

Age-Specific Distributions of Disease Incidence

Age-specific distributions of disease incidence can be linear or multimodal.

Linear trend—incidence of cancer

Multimodal (having several peaks in incidence)

Tuberculosis—peaks at ages 0 to 4 and ages 20-29

Meningococcal disease—peaks among infants younger than age 1 year and teenagers about 18 years old

Latency Effects

Age effects on mortality may reflect the long latency period between environmental exposures and subsequent development of disease.

Biologic Clock Phenomenon

Waning of the immune system may result in increased susceptibility to disease, or aging may trigger appearance of conditions believed to have genetic basis.

Example: Alzheimer’s disease

9

Sex Differences: Males

All-cause age-specific mortality rates is higher for men than for women.

May be due to social factors

May have biological basis

Men often develop severe forms of chronic disease.

Generally, death rates for both sexes are declining.

10

Sex Differences: Female Paradox

Reports from the 1970s indicated female age-standardized morbidity rates for many acute and chronic conditions were higher than rates for males, even though mortality was higher among males.

Higher female rates for:

Pain

Asthma

Some lung difficulties

Cancer

Cancer of the lung and bronchus is leading cause of cancer death for both men and women in the U.S.

Increases among women are related to changes in lifestyle and risk behavior, e.g., smoking.

CHD among Women

Coronary heart disease (CHD) is the leading cause of mortality among women (and also men).

Women may not be alert for symptoms of CHD and fail to seek needed treatment.

Minority Women in Economically Disadvantaged U.S. Areas

In Los Angeles County, some have higher rates of diabetes and hypertension than men.

A large percentage are physically inactive.

High rates of obesity among Latinas and African Americans.

Marital Status

Categories

Single or non-married (e.g., never married, divorced, widowed)

Married

Living with a partner

Marital Status (cont’d)

In general, married people tend to have lower rates of morbidity and mortality.

Examples: chronic and infectious diseases, suicides, and accidents.

Never married adults (especially men) less likely to be overweight

11

Marital Status (cont’d)

Marriage may operate as a protective or selective factor.

Protective hypothesis: marriage provides an environment conducive to health.

Selective hypothesis: people who marry are healthier than people who never marry.

Marital Status (cont’d)

Widowed persons

Suicide rates

Elevated among young white males who were widowed

Depression

Elevated rates among widowed persons

General Comments About Race

U.S. is becoming increasingly more diverse.

Race is an ambiguous concept that overlaps with other dimensions.

Some scientists propose that race is primarily a social and cultural construct.

Measurement of Race

Census 2000 changed the race category by allowing respondents to choose one or more race categories.

Census 2000 used five categories of race.

Census 2010 continued with this classification scheme (Refer to Exhibit 4-1 in text).

Race/Ethnicity Categories Discussed in Chapter 4

African American

American Indian

Asian

Hispanic/Latino

African Americans

In a classic study of differential mortality in U.S., they had the highest rate of mortality of all groups studied.

Higher blood pressure levels

Possible influence of stress or diet.

Higher rates of hypertensive heart disease.

In 2007, age-adjusted death rate for African Americans was 1.3 times rate for whites.

Differences in life expectancy

12

American Indians/Alaska Natives

High rates of chronic diseases, adverse birth outcomes, and some infectious diseases

Pima Indians (1975-1984 data):

High mortality, e.g., male death rate (ages 25 to 34) was 6.6 times that for all races in U.S.

Infectious diseases were the 10th leading cause of death.

13

Asians

Japanese Americans have lower mortality rates than whites.

Lower rates of CHD and cancer.

Low CHD rates attributed to low-fat diet and institutionalized stress-reducing strategies.

Some Asian groups, e.g., Cambodian Americans, have high smoking rates.

TB rates are highest among Asian/Pacific Islander group.

14

Acculturation

Defined as modifications that individuals or groups undergo when they come in contact with another country

Provides evidence of the influence of environmental and behavioral factors on chronic disease

Example: Japanese migrants experience a shift in rates of chronic disease toward those of the host country.

15

Hispanics/Latinos

Hispanic Health and Nutrition Examination Survey (HHANES).

Examined health and nutrition status of major Hispanic/Latino populations in the U.S.

San Antonio Heart Study

Found high rates of obesity and diabetes among Mexican Americans

Hispanic mortality paradox (text box)

16

Nativity and Migration

Nativity--Place of origin of the individual

Categories are foreign born and native born.

Nativity and migration are related.

17

Impact of Migration

Importation of “Third World” disease by immigrants from developing countries

Leprosy during 1980s

Programmatic needs resulting from migration:

Specialized screening programs (tuberculosis and nutrition)

Familiarization with formerly uncommon (in U.S.) tropical diseases

Healthy Migrant Effect

Observation that healthier, younger persons usually form the majority of migrants

Often difficult to separate environmental influences in the host country from selective factors operative among those who choose to migrate

Religion

Certain religions prescribe lifestyles that may influence rates of morbidity and mortality.

Example: Seventh Day Adventists

Follow vegetarian diet and abstain from alcohol and tobacco use

Have lower rates of CHD, reduced cancer risk, and lower blood pressure

Similar findings for Mormons

18

Socioeconomic Status

Low social class is related to excess mortality, morbidity, and disability rates.

Factors include:

Poor housing

Crowded conditions

Racial disadvantage

Low income

Poor education

Unemployment

19

Measurement of Social Class

Variables include:

Prestige of occupation or social position

Educational attainment

Income

Combined indices of two or more of the above variables

20

Hollingshead and Redlich

Studied association of socioeconomic status and mental illness

Classified New Haven, Connecticut, into five social classes based on occupational prestige, education, and address

23

Hollingshead and Redlich Findings

Strong inverse association between social class and likelihood of being a mental patient under treatment.

As social class increased, severity of mental illness decreased.

Type of treatment varied by social class.

24

Mental Health and Social Class

In the U.S., the highest incidence of severe mental illness occurs among the lowest social classes.

Mental Health and Social Class: Two Hypotheses

Social causation explanation (breeder hypothesis)—conditions associated with lower social class produce mental illness.

Downward drift hypothesis—Persons with severe mental disorders move to impoverished areas.

21

Other Correlates of Low Social Class

Higher rate of infectious disease

Higher infant mortality rate and overall mortality rates

Lower life expectancy

Larger proportion of cancers with poor prognosis

May be due to delay in seeking health care

Low self-perceived health status

22

Characteristics of Place

Types of place comparisons:

International

Geographic (within-country) variations

Urban/rural differences

Localized occurrence of disease

25

International Comparisons of Disease Frequency

World Health Organization (WHO) tracks international variations in rates of disease.

Infectious and chronic diseases show great variation across countries.

Variations are attributable to climate, cultural factors, dietary habits, and health care access.

The U.S. fell in the bottom half of OECD countries for both male and female life expectancy; Japan was highest.

26

Within-Country Variations in Rates of Disease

Due to variations in climate, geology, latitude, pollution, and ethnic and racial concentrations

In U.S., comparisons can be made by region, state, and/or county.

Examples include: higher rates of leukemia in Midwest; state by state variations in infectious, vector-borne, parasitic diseases

27

Urban/Rural Differences in Disease Rates

Urban

Diseases and mortality associated with crowding, pollution, and poverty

Example: lead poisoning in inner cities

Homicide in central cities

Rural

Mortality (among all age groups) increases with decreasing urbanization.

Health risk behaviors higher in rural South

28

Standard Metropolitan Statistical Areas (SMSAs)

Established by the U.S. Bureau of the Census to make regional and urban/rural comparisons in disease rates

Metropolitan Statistical Areas (MSAs)

Provide a distinction between metropolitan and nonmetropolitan areas by type of residence, industrial concentration, and population concentration

35

Definition of MSA

Used to distinguish between metropolitan and nonmetropolitan areas

Metropolitan area—large population nucleus together with adjacent communities

Six urban-classification levels used by the National Center for Health Statistics (refer to text.)

Census Tracts

Small geographic subdivisions of cities, counties, and adjacent areas

Each tract contains about 4,000 residents.

Are designed to provide a degree of uniformity of population economic status and living conditions in each tract

36

Localized Place Comparisons

Disease patterns are due to unique environmental or social conditions found in particular area of interest. Examples include:

Fluorosis: associated with naturally occurring fluoride deposits in water.

Goiter: iodine deficiency formerly found in land-locked areas of U.S.

29

Geographic Information Systems (GIS)

A method to provide a spatial perspective on the geographic distribution of health conditions

A GIS produces a choroplath map that shows variations in disease rates by different degrees of shading.

Reasons for Place Variation in Disease

Gene/environment interaction

Examples: sickle-cell gene; Tay-Sachs disease.

Influence of climate

Examples: yaws, Hansen’s disease

Environmental factors

Example: chemical agents linked to cancer

30

Characteristics of Time

Cyclic fluctuations

Point epidemics

Secular time trends

Clustering

Temporal

Spatial

31

Cyclic Fluctuations

Periodic changes in the frequency of diseases and health conditions over time

Examples:

Birth rates

Higher heart disease mortality in winter

Influenza

Unintentional injuries

Meningococcal disease

Rotavirus infections

Cyclic Fluctuations (cont’d)

Related to changes in lifestyle of the host, seasonal climatic changes, and virulence of the infectious agent

Common Source Epidemic

Outbreak due to exposure of a group of persons to a noxious influence that is common to the individuals in the group

Types: point epidemic; continuous common source epidemic

Refer to Figure 4-22 for an example an influenza outbreak in a residential facility.

Point Epidemics

The response of a group of people circumscribed in place and time to a common source of infection, contamination, or other etiologic factor to which they were exposed almost simultaneously.

Examples: foodborne illness; responses to toxic substances; infectious diseases.

32

Influenza-Related Illness at a Residential Facility

Secular Time Trends

Refer to gradual changes in the frequency of a disease over long time periods.

Example is the decline of heart disease mortality in the U.S.

May reflect impact of public health programs, dietary improvements, better treatment, or unknown factors.

33

Clustering

Case clustering--refers to an unusual aggregation of health events grouped together in space and time

Temporal clustering: e.g., post-vaccination reactions, postpartum depression

Spatial clustering: concentration of disease in a specific geographic area, e.g., Hodgkin’s disease