What is Epidemiology? (1) Epidemiologic basis of public health What is Epidemiology? (1) Epidemiology is that field of medical science which is concerned with the relationship of various factors and conditions which determine the frequencies and distributions of an infectious process, a disease, or a physiologic state in a human community. (Maxcy) Detels - PH150 - 2 Oct 2013

What is Epidemiology? (2) Epidemiologic basis of public health What is Epidemiology? (2) 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 of health problems (Last) Detels - PH150 - 2 Oct 2013

What is Epidemiology? (3) Epidemiologic basis of public health What is Epidemiology? (3) Epidemiology is a strategy for the study of factors relating to the etiology, prevention, and control of disease; to promote health; and to efficiently allocate efforts and resources for health promotion, maintenance and medical care in human populations. (Detels) Detels - PH150 - 2 Oct 2013

Epidemiologic basis of public health EPI DEMOS LOGOS upon people study Epidemiology is a philosophy, a strategy, a methodology, a way of studying a health problem. Epidemiology is not a body of knowledge. Detels - PH150 - 2 Oct 2013

Two Holy Trinities of Epidemiology Epidemiologic basis of public health Two Holy Trinities of Epidemiology Disease characteristics: agent host environment Health is a state of equilibrium between: Agent Host  Environment Detels - PH150 - 2 Oct 2013

Two Holy Trinities of Epidemiology (2) Epidemiologic basis of public health Two Holy Trinities of Epidemiology (2) Disease descriptors: Time Place Person Epidemiologists describe disease/states in terms of time, place and person Detels - PH150 - 2 Oct 2013

Ultimate truth = denominator Epidemiologic basis of public health Ultimate truth = denominator Detels - PH150 - 2 Oct 2013

Epidemiologic basis of public health Incidence = # of New Cases Occurring in a Given Population in a Specified Time Period_ Population at Risk in That Time Period (Speedometer) Detels - PH150 - 2 Oct 2013

Epidemiologic basis of public health Prevalence = # of Cases Existing in a Given Population at a Single Point in Time__ Population at That Time (odometer) Detels - PH150 - 2 Oct 2013

Epidemiologic basis of public health An example of the use of time, place, and person to describe disease characteristics: Gathering evidence Ordering hypotheses by probability Observing place, time (trend), and person characteristics Detels - PH150 - 2 Oct 2013

Epidemiologic basis of public health Detels - PH150 - 2 Oct 2013

Epidemiologic basis of public health Detels - PH150 - 2 Oct 2013

Epidemiologic basis of public health Detels - PH150 - 2 Oct 2013

Epidemiologic basis of public health Detels - PH150 - 2 Oct 2013

Epidemiologic basis of public health Detels - PH150 - 2 Oct 2013

Epidemiologic basis of public health Detels - PH150 - 2 Oct 2013

Epidemiologic basis of public health Detels - PH150 - 2 Oct 2013

Epidemiologic basis of public health Detels - PH150 - 2 Oct 2013

Epidemiologic basis of public health Detels - PH150 - 2 Oct 2013

Epidemiologic basis of public health Reported incidence of disease X 1925-1962, Los Angeles Detels - PH150 - 2 Oct 2013

WHAT DRIVES AN EPIDEMIC Reproductive number – number of secondary infections from one case Transmission probability per contact Contact rate/frequency Duration of infectiousness Available susceptibles Agent characteristics

REPRODUCTIVE NUMBER R = number of secondary infections from one individual Ro = reproductive at the beginning of epidemic R > 1 Epidemic spreads R < 1 Epidemic dies out R subject to changes in presence and levels of determinants of epidemic spread

Epidemiologic basis of public health Public health is concerned with health of the public; i.e., populations. Epidemiology is the method/strategy of studying disease/health in human populations. Epidemiology is therefore the core science of public health. Detels - PH150 - 2 Oct 2013

Uses of Epidemiology (1) Epidemiologic basis of public health Uses of Epidemiology (1) a. Community diagnosis; i.e., what are the major health problems occurring in a community b. Establishing the history of a disease in a population; e.g., identifying the periodicity of an infectious disease c. Describing the natural history of disease in the individual; e.g., natural history of HIV infection in the individual (infection-acute syndrome-asymptomatic phase-clinical disease-death) Detels - PH150 - 2 Oct 2013

Uses of Epidemiology (2) Epidemiologic basis of public health Uses of Epidemiology (2) d. Describing the clinical picture of disease; i.e., who gets the disease, who dies from the disease, and what the outcome of the disease is Estimating risk; e.g., what factors increase the risk of heart disease, automobile accidents, and violence f. Identifying syndromes and precursors; e.g., the relationship of high blood pressure to stroke, kidney disease, and heart disease Detels - PH150 - 2 Oct 2013

Uses of Epidemiology (3) Epidemiologic basis of public health Uses of Epidemiology (3) g. Evaluating prevention/intervention programs; e.g., vaccine and clinical trials h. Investigating epidemics/diseases of unknown etiology i. Assessing the cost-effectiveness of interventions j. Assessing strategies to translate science to action (“implementation science”) Detels - PH150 - 2 Oct 2013