Chap 3: Epidemiology: The Study of Disease, Injury, and Death in the Community Anita Sego Spring, 2005

Chap 3: Epidemiology: The Study of Disease, Injury, and Death in the Community

Anita Sego

Spring, 2005

Chap 3: Epidemiology

Chapter Objectives

• Define the terms epidemic, epidemiology, and epidemiologist, and explain their importance in community health.

• List some diseases that causes epidemics in the past and some that are causing epidemics today.

• Discuss how the practice of epidemiology has changes since the days of Benjamin Rush and John Snow.


Chapter Objectives

• Explain why rates are important in epidemiology and list some of the commonly used rates.

• Define incidence and prevalence rates and provide and example of each

• Calculate a variety of rates from the appropriate data.

• Discuss the importance of disease reporting to a community’s health and describe the reporting process.


Chapter Objectives

• Identify sources of standardized data used by epidemiologists, community health workers, and health officials and list the types of data available from each source.

• Define the following standardized measurements of health status - life expectancy, years of potential life lost (YPLL), disability-adjusted life expectancy (DALEs).


DefinitionsEpidemiologyEpidemiology

– is “the study of the distribution and determinants of diseases and injuries in human populations.” Mausner & Kramer, 1985Mausner & Kramer, 1985

Endemic DiseasesEndemic Diseases– a disease that occur regularly in a population

EpidemicEpidemic– an unexpectedly large number of cases of

disease in a particular population


Recent Epidemics in the United States

Disease Cases/Prev. yrs Period # Disease Cases/Prev. yrs Period # of Casesof Cases

St. Louis 5-72 1975 St. Louis 5-72 1975 1,815 1,815encephalitisencephalitis

Legionnaires’ Unknown 1976 Legionnaires’ Unknown 1976 235 235

AIDS Unknown 1981-1999 AIDS Unknown 1981-1999 733,374 733,374

Lyme Disease Unknown 1990-1999 Lyme Disease Unknown 1990-1999 121,000 121,000


Definitions

Epidemiologist– one who practices epidemiology

Epizootiologist– one who studies disease outbreaks in animals

Pandemic– an outbreak of disease over a wide geographical

area such as a continent– influenza pandemic of 1918-1919 killed 25 million

people worldwide


History of Epidemiology

• 300 B.C. - Hippocrates “Father of Medicine”– suggested a relationship between the occurrence of

disease and the physical environment.

• 1793 - Yellow fever in Philadelphia– Killed 4,044 People– Cause discovered in 1901 by Walter Reed - Mosquito

• 1849 - Cholera in London– Dr. John Snow investigated – 30 years before Pasteur “Germ Theory of disease”


Numbers and Rates

• Case Definition or “What”– a set of criteria for deciding whether a

person has a particular disease or other health-related condition

• Rates– the number of events that occur in a given

population in a given period of time

• Importance of Rates– allow for a comparison of outbreaks that

occur at different times or in different places


3 Important Kinds of Rates

Natality (birth) rate =Natality (birth) rate =

# of live births to residentsin an area in a calendar year

Morbidity (disease) rate Morbidity (disease) rate = =

# of cases of residents with illnessin an area in a calendar year

Mortality (fatality) rate Mortality (fatality) rate ==

# of deaths to residentsin an area in a calendar year

Population in the area in the same year




3 Important Types of Rates

Incidence rate =Incidence rate =

# # of new cases of a diseasein a certain time period

Prevalence rate =Prevalence rate =# of new and old cases of a disease

in a certain time period

Attack rate =Attack rate =# of new cases in a narrowly

defined population during a specific time periodPopulation at risk in same time period

Population at risk in same time period

Population at risk in same time period


Crude & Specific Rates

Crude death rate =Crude death rate = Number of deaths (all causes)

Cause-specific death rate =Cause-specific death rate =

Number of deaths (35-44)Age-specific death rate =Age-specific death rate =

Number of deaths (specific cause)

Estimated midyear population

Estimated midyear population (35-44)

Estimated midyear population


Reporting Births, Deaths, & Diseases

Doctors

Clinics

Hospitals

Local HealthDepartment

State HealthDepartment

Centers for Disease Control and

Prevention (CDC)


Sources of Standardized Data

• U.S. Census– conducted every 10 years, enumeration of

population

• Statistical Abstract of the U.S.– statistics on social, political, & economic

organization

• Vital Statistics– statistical summaries of records of major life

events


Sources of Standardized Data

• Morbidity & Mortality Weekly Reports (MMWR)– lists cases of notifiable diseases in the U.S.

• National Health Surveys– health interviews of people– clinical tests, measurement, and physical

examinations – survey of places where people receive medical care

• NHIS NHANES BRFSS YBRS NHCS


Standardized Measurements of Health Status• Mortality Statistics

• Life Expectancy

• Years of Potential Life Lost

• Disability-Adjusted Life years

• Disability-Adjusted Life Expectancy


Epidemiological Study Measures• Probability statements or testing the differences

in groups

• Cohort Study– Relative Risk: measure of association between

incidence of disease in unexposed group & exposed group

• Case/Control Study– Odds Ratio: Estimates “relative risk” because incidence

measures can not be obtained from two groups

• Experimental– Use statistical t-test, or F-test to test probability of

differences between groups


Epidemiological Studies

• Descriptive Studies – “Who” or Person

• Age, Sex, Ethnic, Race, Socioeconomic Status– “When” or Time

• Time of day, week, month, season, year, decades• incubation period

– “Where” or Place • country, state, county, street, urban or rural,

domestic or foreign, institutional or noninstitutional.



• Analytical Studies - testing of hypotheses about relationships between health problems– 2 Basic Types

• Case/Control Study (Retrospective)

• Cohort Study (Prospective study)



• Experimental– a study carried out under controlled

conditions


Epidemiology:Epidemiology:The Study of The Study of

Disease, Injury, and DeathDisease, Injury, and Death in the Communityin the Community

Chapter 3

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Chap 3: Epidemiology: The Study of Disease, Injury, and Death in the Community Anita Sego Spring, 2005