PHHE 295. Chapter 3. Epidemiology: The Study of Disease, Injury, and Death in the Community

PHHE 295

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

Chapter Objectives:

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

2)      List some diseases that caused epidemics in the past and some that are causing epidemics today.

3)      Discuss how the practice of epidemiology has changed since the days of Benjamin Rush and John Snow.

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

5)      Define incidence and prevalence rates and provide examples of each.

6)      Calculate a variety of rates from the appropriate data.

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

8)      Define the following standardized measurements of health status—life expectancy, years of potential life lost, disability-adjusted life years, and the health-adjusted life expectancy.

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

10)   List and describe the various types of epidemiological studies and explain the purpose of each.

Key Terms

·         Epidemiology: The study of the distribution and determinants of health-related states or events in specified populations.

·         Epidemic: An unexpectedly large number of cases of an illness, specific health-related behavior, or other health-related event in a particular population.

·         Endemic Disease: A disease that occurs regularly in a population as a matter of course.

·         Epidemiologist: One who practices epidemiology.

·         Pandemic: An outbreak of disease over a wide geographical area such as a continent.

·         Cases: People afflicted with a disease.

·         Rate: The number of events that occur in a given population in a given period of time.

·         Natality (Birth) Rate: The number of live births divided by total population.

·         Morbidity Rate: The rate of illness in a population.

·         Mortality (Fatality) Rate: The number of deaths in a population divided by the total population.

·         Population At Risk: Those in the population who are susceptible to a particular disease or condition.

·         Incidence Rate: The number of new health-related events or cases of a disease in a population exposed to that risk during a particular period of time, divided by the total number in that same population.

·         Acute Disease: A disease that lasts three months or less.

·         Prevalence Rate: The number of new and old cases of a disease in a population in a given period of time, divided by the total number in that population.

·         Chronic Disease: A disease or health condition that lasts longer than 3 months.

·         Attack Rate: An incidence rate calculated for a particular population for a single disease outbreak and expressed as a percentage.

·         Crude Rate: A rate in which the denominator includes the total population.

·         Crude Birth Rate: The number of live births per 1,000 in a population in a given period of time.

·         Crude Death Rate: The number of deaths per 1,000 in a population in a given period of time.

·         Age-Adjusted Rate: Rate used to make comparisons of relative risks across groups and over time when groups differ in age structure.

·         Specific Rate: A rate that measures morbidity or mortality for particular populations or diseases.

·         Cause-Specific Mortality Rate: The death rate due to a particular disease.

·         Case Fatality Rate: The percentage of cases of a particular disease that result in death.

·         Proportionate Mortality Ratio: The percentage of overall mortality in a population that is attributable to a particular case.

·         Notifiable Diseases: Infectious diseases for which health officials request or require reporting for public health reasons.

·         National Electronic Telecommunications System: The electronic reporting system used by state health departments and the CDC.

·         Life Expectancy: The average number of years a person from a specific cohort is projected to live from a given point in time.

·         Years of Potential Life Lost: The number of years lost when death occurs before the age of 65 or 75.

·         Disability-Adjusted Life Years: A measure for the burden of disease that takes into account premature death and loss of healthy life resulting from disability.

·         Health-Adjusted Life Expectancy: The number of years of healthy life expected, on average, in a given population.

·         U.S. Census: The enumeration of the population of the United States that is conducted every 10 years.

·         Vital Statistics: Statistical summaries of records of major life events such as births, deaths, marriages, divorces, and infant deaths.

·         Descriptive Study: An epidemiological study that describes an epidemic with respect to person, place, and time.

·         Epidemic Curve: A graphic display of the cases of disease according to the time or date of onset symtoms.

·         Point Source Epidemic Curve: An epidemic curve depicting a distribution of cases that all can be traced to a single source of exposure.

·         Incubation Period: The period between exposure to a disease and the onset of symptoms.

·         Propagated Epidemic Curve: An epidemic curve depicting a distribution of cases traceable to multiple sources of exposure.

·         Analytic Study: An epidemiological study aimed at testing hypotheses.

·         Risk Factors: Factors that increase the probability of disease, injury, or death.

·         Observational Study: An analytic, epidemiological study in which the investigator observes the natural course of events, noting exposed and unexposed subjects and disease development.

·         Case/Control Study: A study that seeks to compare those diagnosed with a disease with those who do not have the disease for prior exposure to specific risk factors.

·         Cohort Study: An epidemiological study in which a cohort is classified by exposure to one or more specific risk factors and observed to determine the rates at which disease develops in each class.

·         Cohort: A group of people who share some important demographic characteristic.

·         Odds Ratio: A probability statement about the association between a particular disease and a specific risk factor, resulting from a case/control study.

·         Relative Risk: A statement of the relationship between the risk of acquiring a disease when a specific risk factor is present and the risk of acquiring that same disease when the risk factor is absent.

·         Experimental Studies: Analytic studies in which the investigator allocates exposure or intervention and follows development of disease.

·         Placebo: A blank treatment.

Chapter Summary

·         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 control health problems.

·         Rates of birth, death, injury and disease are essential tools for epidemiologists.

·         Incidence rates are a measure of the number of new cases of disease, injury, or death in a population over a given period of time. Prevalence rates measure all cases. An attack rate is a special kind of incidence rate used for a single outbreak.

·         Cases of certain diseases, called notifiable or reportable diseases, are reported by doctors, clinics, medical laboratories, and hospitals to local health agencies. These agencies then report them to state health agencies, who then forward the data to the CDC. These reports assist epidemiologists who study disease trends.

·         The health status of a population or community can be measured in a number of different ways, including mortality statistics, life expectancy, years of potential life lost, disability-adjusted life years, and health-adjusted life expectancy.

·         Epidemiologists conduct three general types of studies to learn about disease and injury in populations—descriptive studies, analytic studies, and experimental studies.

·         Descriptive studies describe the extent of outbreaks in regard to person, place, and time.

·         Analytic studies test hypotheses regarding associations between diseases and risk factors.

·         Analytic studies can be either observational or experimental.

·         Observational studies can be either case/control or cohort in design.

·         Experimental studies examine the effects of specific factors under carefully controlled conditions.

·         Criteria for judging whether an association identified in epidemiological studies represents a casual relationship include strength of association, consistency, specificity, temporal correctness, and biological plausibility.

·         Epidemiological studies provide the data and information that enable public health officials and policy makers to make decisions and take actions to improve health.