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.
Chap 3: Epidemiology
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.
Chap 3: Epidemiology
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).
Chap 3: Epidemiology
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
Chap 3: Epidemiology
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
Chap 3: Epidemiology
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
Chap 3: Epidemiology
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”
Chap 3: Epidemiology
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
Chap 3: Epidemiology
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
Population in the area in the same year
Population in the area in the same year
Chap 3: Epidemiology
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
Chap 3: Epidemiology
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
Chap 3: Epidemiology
Reporting Births, Deaths, & Diseases
Doctors
Clinics
Hospitals
Local HealthDepartment
State HealthDepartment
Centers for Disease Control and
Prevention (CDC)
Chap 3: Epidemiology
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
Chap 3: Epidemiology
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
Chap 3: Epidemiology
Standardized Measurements of Health Status• Mortality Statistics
• Life Expectancy
• Years of Potential Life Lost
• Disability-Adjusted Life years
• Disability-Adjusted Life Expectancy
Chap 3: Epidemiology
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
Chap 3: Epidemiology
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.
Chap 3: Epidemiology
Epidemiological Studies
• Analytical Studies - testing of hypotheses about relationships between health problems– 2 Basic Types
• Case/Control Study (Retrospective)
• Cohort Study (Prospective study)
Chap 3: Epidemiology
Epidemiological Studies
• Experimental– a study carried out under controlled
conditions
Chap 3: Epidemiology
Epidemiology:Epidemiology:The Study of The Study of
Disease, Injury, and DeathDisease, Injury, and Death in the Communityin the Community
Chapter 3