Epidemiology BS Public Health 2024 PDF

# Introduction to Epidemiology ## Dr Ishtiaque Ali Bhan (DPT) MSPH SZABIST Karachi ## Meaning of Epidemiology Epidemiology is derived from the Greek word "Epidemic" - **EPI**: On/upon - **DEMOS**: People - **LOGOS**: Study of **Epidemiology means the study of disease in human populations....

# Introduction to Epidemiology ## Dr Ishtiaque Ali Bhan (DPT) MSPH SZABIST Karachi ## Meaning of Epidemiology Epidemiology is derived from the Greek word "Epidemic" - **EPI**: On/upon - **DEMOS**: People - **LOGOS**: Study of **Epidemiology means the study of disease in human populations.** ## Definition "The study of the distribution and determinants of health-related states or events in specified populations, and the application of this study for the prevention and control of health problems". **As defined by John M. Last (1988)** ## Definition ... ### Distribution - **Frequency** refers not only to the number of health events such as the number of cases of meningitis or diabetes in a population but also to the relationship of that number to the size of the population. The resulting rate allows epidemiologists to compare disease occurrence across different populations. - **Pattern** refers to the occurrence of health-related events by time, place, and person. ### Determinants - **Determinants** are the causes and other factors that influence the occurrence of disease and other health-related events. - Illness does not occur randomly in a population, but happens only when the right accumulation of risk factors or determinants exists in an individual. ## Other Definitions ... - The epidemiology is that branch of medical science which deals with epidemics (Parkin, 1873). - Epidemiology is the study of any disease, as a mass phenomenon (Greenwood, 1934). - It is the study of the disease frequency, distribution and determinants among man (Mac Mohan- 1960). ## Aims - To describe and measure the magnitude of health and disease problems in human populations. - To identify etiological factors in the pathogenesis of the disease. - To provide the data essential to the planning, implementation and evaluation of services for the prevention and control of the disease and to the setting up of priorities among those services. ## Objectives - To identify the etiology or cause of disease. - To determine the extent of disease. - To study the progression of disease. - To evaluate preventive and therapeutic measures for a disease or condition. - To develop public health policy. ## History of Epidemiology ### John Snow - Father of epidemiology Snow conducted studies in 1854 when an epidemic of cholera erupted in the Golden Square of London. He began his investigation by determining where in this area persons with cholera lived and worked. He marked each residence on a map of the area. Snow believed that water was a source of infection for cholera, he marked the location of water pumps on his spot map, then looked for a relationship between the distribution of households with cases of cholera and the location of pumps. He noticed that more case households clustered around Pump A. However, that no cases of cholera had occurred in a two-block area just to the east of the broad street pump. Upon investigating, Snow found a brewery located there with a deep well on the premises. Brewery workers got their water from this well and also received a daily portion of liquor. Access to these uncontaminated rations could explain why none of the brewery's employees contracted cholera. ### Hippocrates - “Environmental Influences” On essay entitled "On Airs, Waters, and Places," Hippocrates suggested that environmental and host factors such as behaviors might influence the development of disease. ## Scope of Epidemiology 1. **Causation of the disease:** - Most of diseases are caused by interaction between genetic and environmental factors. (Diabetes) - Personal behaviors affect this interplay. - Epidemiology is used to study their influence and the effects of preventive interventions through health promotion. 2. **Natural history of the disease:** - Epidemiology is also concerned with the course and outcome (natural history) of diseases in individuals and groups. ### Natural History of Disease Hence it refers to the progression of a disease process in an individual over time, in the absence of treatment. For example, untreated infection with HIV causes a spectrum of clinical problems beginning at the time of seroconversion (primary HIV) and terminating with AIDS and usually death. | Stage | Description | | :----------------------------- | :------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | Stage of Susceptibility | | | Stage of Subclinical Disease | | | Stage of Clinical Disease | | | Stage of Recovery, Disability or Death | | | Usual Time of Diagnosis | Pathologic Changes | Onset of Symptoms | | :----------------------- | :------------------ | :----------------- | | | | | 3. **Health status of the population:** - Epidemiology is often used to describe the health status of the population. - Knowledge of the disease burden in populations is essential for health authorities. - To use limited resources to the best possible effect by identifying priority health programmes for prevention and care. 4. **Evaluation of Interventions:** - To evaluate the effectiveness and efficiency of health services. * This means determining things such as - * Impact of Contraceptive use on Population Control. * the efficiency of sanitation measures to control diarrheal diseases ## Uses of Epidemiology The uses of epidemiology are: - To study the health history of the population and their disease trends. - To arrive at community Diagnosis. - To plan and evaluate health services. - To estimate individuals’ risk and chance. - To define and redefine syndromes. - To complete the natural history of disease. - To search for causes of health and disease by employing epidemiological methods. ## Terminologies Used in Epidemiology ### Infection  The entry and development or multiplication of an infectious agent in the body of man or animal. ### Epidemic  An epidemic is the rapid spread of infectious disease to a large number of people in a given population within a short period of time. ### Endemic The constant presence of a disease or infectious agent within a given geographical area or population group, without importation from outside. Eg. Common cold. ### Pandemic An epidemic which spreads from country to country or over the whole world. Eg. AIDS ### Zoonosis Diseases or infections which are transmitted from vertebrate animal to human. Eg. Rabies, plague ### Reservoir The habitat (place for living) where an infectious agent living, grows and multiplies. ### Carrier  Disease carrier could refer to: Asymptomatic carrier, a person or organism infected with an infectious disease agent, but displays no symptoms. ### Isolation A separation of a person with infectious disease from contact with other human beings for the period of communicability. ### Incubation Period This is the time interval between the entry of the disease agent into the body and the appearance of first sign and symptom of the disease. ### Pathogenicity  Ability to cause the disease. ### Contagious  A disease that is transmitted through direct contact. Eg. STD, flu..etc ### Virulence Measure the severity of disease. ### Fomites Inanimate articles other than food or water contaminated by the infectious discharges. e.g. Clothes, utensil, furniture etc. ### Vector Usually an arthropod eg. Mosquito which transfers an infectious agent from an infected person to a healthy person. Ticks, mites, lice etc.