 A public health science (foundation of public health)  Impacts personal decisions about our lifestyles  Affects government, public health agency and medical organization policy decisions

 Epidemiology derives from epidemic, a term that provides an immediate clue to its subject matter.  Originates from the Greek words epi (upon) + demos (people) + logy (study of)

 Friis & Sellers 2009, defines epidemiology as concerned with the distribution and determinants of health and diseases, morbidity, injuries, disability, and mortality in populations.  Application of this study to control and prevent health problems in populations.

 In the past, main causes of death were due to a single pathogen (disease causing microorganism or related substance)  Epidemiologists had the challenge of isolating a single bacteria, virus, or parasite

 The discipline of epidemiology underwent dramatic changes in the first half of the 20th century.  A new kind of epidemiology came into being as a discipline in the decades following the Second World War variously referred to as “modern” or “risk factor” epidemiology (Parascandola, 2011).

 The new epidemiology differed from earlier forms of epidemiology in that it included a focus on chronic rather than infectious diseases, an emphasis on identifying individual risk factors for disease, and use of advanced quantitative methodology (Parascadola, 2011).

Study of the health and disease of the “body politic” – the population. Basic science of public health What causes disease? How does disease spread? What prevents disease? What works in controlling disease?

 Descriptive  Analytic

 Descriptive epidemiology involves characterization of the distribution of health- related states or events by:  Person – who?  Place – where?  Time – when?  Clinical criteria – what?

 Describes frequency and patterns of diseases/conditions  Planning, conduction, and evaluation of effective health education, screening, prevention, and control programs

 Identifying and quantifying associations  Testing hypotheses, and identifying causes of health-related states or events  Explains why and how health-related states or events occur

 Classic descriptors of how common a disease, symptom, or problem is in a population  Incidence- measures the occurrence of new disease in a population  Prevalence - measures the existence of current disease in a population

 Incidence: Fraction of a group initially free of the condition that go on to develop it during a given time period.  How measured? ▪ By identifying group of susceptible people (free of disease) and examining them periodically in order to discover and count new cases that develop during interval.

 Incidence is calculated as the number of new cases of a disease or condition in a specified time period (usually a year) divided by the size of the population under consideration who are initially disease free.  Example:  For example, the incidence of meningitis in the UK in 1999 could be calculated by finding the number of new meningitis cases registered during 1999 and dividing that number by the population of the UK.

 Prevalence: The fraction (proportion) of a group processing a clinical condition at a given point in time  How measured? ▪ By surveying a defined population containing people with and without the clinical condition at a single point in time (snap-shot in time)

 The prevalence is calculated by dividing the number of persons with the disease or condition at a particular time point by the number of individuals examined.  For example: ▪ In a study, 6139 individuals completed a questionnaire (were examined). Of these 6139 people, 519 currently suffered incontinence and so had the condition at the particular time point of the study. Thus the prevalence of incontinence was 519/6139 = 0.085

 Prevalence is often expressed as a percentage, calculated by multiplying the ratio by 100.  The above study expresses prevalence as a percentage, thus the prevalence of incontinence is 8.5% (or rounded is 9%)

 Frequency: the number of time an event occurs  Epidemiology studies the number of times a disease occurs ▪ It answers the question- How many? ▪ Epidemiology is a quantitative study

 Distribution: Distribution of an event by person, place and time  Epidemiology studies distribution of disease ▪ It answers the question: who, where, and when?

 Determinants: Factors or events that are capable of bringing about a change in health(Friis & Sellers, 2009)  Epidemiology studies what determines health events  It answers the question : how and why?

 Endemic: Persistent, usual, expected health- related state or event in a defined population over a given period of time  Epidemic: outbreak of one specific disease in excess of what would be normally expected (W. Nile)  Pandemic: Epidemic affecting a large number of people, many countries, continents, or regions

 Identifying causes of disease and the mechanisms by which they spread remains a primary focus of epidemiology  Etiology: Science and study of the causes of disease and their mode of operation

 The sum of all factors contributing to the occurrence of the disease  Agent factors + Host factors + Environmental factors = Etiology of Disease

 When an infectious disease is contagious, or capable of being communicated or transmitted, it is called a communicable disease  Communicable diseases spread through air, water, food, and contact.  Examples: ▪ HIV/AIDS ▪ Hanta virus ▪ Bird flu

 Some — but not all — infectious diseases spread directly from one person to another. Infectious diseases that spread from person to person are said to be contagious (communicable).  Some infections spread to people from an animal or insect, but are not contagious from another human. ▪ Lyme disease is an example: You can't catch it from someone you're hanging out with or pass in the street. It comes from the bite of an infected tick.