HLSC 4613Principles of Epidemiology Instructor: Ches Jones, PhD University of Arkansas
Contents • Unit One-Introduction and Definitions • Unit Two-Rates and Measurements • Unit Three-Descriptive Epidemiology • Unit Four-Analytic Epidemiology • Unit Five-Screening and Surveillance
Unit One Introduction and Definitions
Epidemiology-Definition Branch of medicine dealing with a combination of knowledge and research methods concerned with the distribution and determinants of health and illness in populations, and with contributors to health and control of health problems.
Main Components of Epi • An analytic, descriptive component termed classical epidemiology, and • A diagnosis, management of illness, and critical review of literature termed clinical epidemiology.
Evolution of Modern Epidemiology 3 Eras • Miasma (Sanitary statistics) • Disease due to bad air. • Prior to 1850 • Infectious Disease (Germ theory) • 1850-1930 • Chronic Disease (Black box) • 1930-present
Infectious Disease (Acute) • Cause DiagnosisTreatment Severity • Disease of short duration • Affects mainly the young
Chronic Disease • Cause Diagnosis Treatment (cure) • Disease of long induction period • Time allows multiple causes to develop • Affects mainly the old
Public Health Approach Implementation How to do it? Intervention Evaluation What works? Risk Factor Identification What’s the cause? Surveillance What’s the problem? Problem Response
3 Levels of Prevention • Primary- prevention of the development of disease • Secondary- early detection and treatment of disease • Tertiary-rehabilitation and/or restoration of effective functioning after treatment of disease
Epidemiologic Surveillance Definition The ongoing process and systematic collection, analysis, and interpretation of health data in the process of describing and investigating the health status of a population.
Epidemiological Surveillance Two types: Passive-Disease frequency data collected Periodically. Current results not available Active-Disease status is updated constantly. Usually as the result of an outbreak or other identified epidemic. Is more costly than passive surveillance.
Current Uses of Epidemiology • Identifying the etiology and cause of a new epidemic or syndrome. Examples: • Carpal Tunnel Syndrome • Toxic Shock Syndrome • Post Traumatic Stress Syndrome
Current Uses of Epidemiology • Investigating the risk associated with a harmful exposure • Examples: Health risks associated with: • Radon exposure • Lead • Environmental tobacco smoke • Dioxin
Current Uses of Epidemiology • Determine if a treatment is effective. • Results from a study showing survival rates following segmental and total mastectomies.
Current Uses of Epidemiology • Study and identify health service utilization needs and trends. Examples: • Effect of health insurance coverage on health services used by poor and near-poor populations. • Impact of youth violence on emergency room services and utilization
Current Uses of Epidemiology To provide rationalization and justification for health policy planning. Examples: • Smoking bans • Gun-control bans • Drunk-driving laws • Hazardous waste regulations
Aims of Epidemiology • Study occurrence, distribution, and progression of diseases and to describe the health status of a population. • Provide data that will contribute to the understanding of the etiology of health and disease • Promote utilization of epidemiological concepts to the management of health services.
Types of Epi Strategies Used • Descriptive • Analytic (retrospective (case-control), prospective (longitudinal or cohort), and cross-sectional) • Experimental (cause and effect)
Limitations of Epidemiology Difficult to assess risk from epidemiology data because: 1) Research studies on humans are sometimes unethical, expensive, and difficult to obtain. 2) Chronic disease situations often finds very low risk.
Limitations of Epidemiology(Continued) 3) The number of persons with the disease or exposure is very small. 4) Latency period between exposure and disease status are sometimes many years apart. 5) Humans may be exposed to multiple chemical, biological, and physical hazards.
Epidemiological Models • Traditional Model • Health Field Concept • Other Models
Traditional Model Agent Host Environment
Health Field Concept Biology/Heredity Lifestyle Environment Health Care System
Health Field Concept • Lifestyle • Leisure • Consumption patterns • Employment/occupational risks • Environment • Physical • Social Psychological
Health Field Concept • Human Biology • Genetic Inheritance maturation and aging • Medical Care System • Preventive • Restorative • Curative
Use of HFC in Epi • Selection of diseases that are of high risk and contribute to mortality and morbidity. • Allocate resources proportionally to disease occurrences. • Allocate total health expenditures to the four elements of the epidemiology model.
Web of Causation • Shows multiple factors • Antecedents of risk factors • Time • Illustrates complication of disease etiology • Identifies intervention points
Concept of Risk With multiple causes and chronic diseases, epidemiologists like to refer to the concept of causality based on the odds (risks, chances) of the occurrence of disease or health status as associated with the occurrence of a specific exposure (risk/protective factor).
Criteria for determining causality (more applicable to single cause/single effect) • Temporal relationship: a causes b, then a comes first • Specificity: a cause leads to a single effect • Strength or intensity (strong relationship between findings) • Consistency (same association is found study after study) • Coherence (does it make sense?)
Criteria for a Risk factor • Risk increases with increased exposure • Time sequence Risk Factor Disease • Limited or no error involved
Unit Two Epidemiological Measurement
Epidemiological Measurement Mortality Rates Morbidity Rates
Epidemiological Measurement • Where to get data? • Mortality/Vital Statistics • Morbidity/Hospital/Clinic Records • Health Assessments/Behavior Surveys • Surveillance Systems
Measures of Mortality • Crude Mortality Rate • Infant Mortality Rate • Specific Mortality Rate (age, sex, race, and cause) • Case Fatality Rate • Proportionate Mortality Ration (PMR)
Epidemiological Measurements General Formula Number of events (cases, deaths, services) In a specified time period Population at risk of experiencing the event X 10n Some base of ten: 1,000 10,000 100,000
Rates and Risks Reasons to Use Caution When Interpreting Rates and Risks • Ecological Fallacy (generalizing) • Variations in Base (what base is used) • False Association (rates apply to pop’n) • Variance of Rates (differences based on rates)
Crude Mortality Rate All deaths during a calendar year Population at mid-year X 1,000 = deaths per 1,000
Infant Mortality Rate Most widely accepted measure for estimating the health status of a population Number of infant deaths * (less than 1 year of age) Number of live births *excludes fetal deaths X 1,000 (common rate)
Specific Mortality Rates • Before the experiences of two populations can be compared, account must be taken for differences in age, sex, race, or cause. • Rates are adjusted in order to remove the effect of a confounding variable, such as age, sex, or race.
Specific Mortality Rates Examples Mortality Rates Specific For: Age Specific MR: by age group Gender Specific MR: for males, for females Race/Ethnic Group: for white, blacks, etc.
Cause Specific-Mortality Deaths assigned to the specified disease during a calendar year Population at mid-year X 100,000 =deaths per 100,000 population per year
Case Fatality Ratio Number of deaths due to the disease in a specific time period number of cases of the disease in the same time period X 100 Express as %
Case Fatality Ratio This measure represents the probability of death among diagnosed cases, or the killing power of a disease.
Proportionate Mortality Ratio Deaths assigned to the disease in a certain year Total deaths in the population in the same year X 100 Express as %
Proportionate Mortality Ratio Used to describe the proportion of the overall mortality that is ascribed to a specific cause.
Morbidity Rates • Attack Rate • Incidence • Prevalence • Years of Potential Life Lost (YPLL)
Attack Rate An incidence rate used to describe the occurrence of food borne illnesses, infectious diseases, and other acute, short time period diseases. ill ill + well X 100 (%)