Epidemiology Lecture 1 Introduction PDF

Epidemiology Dr. Asma Sayedali BDS UofK MD SMSB Course contents 1-Introduction to epidemiology. 2-Measuring health and disease. 3-Causation in epidemiology. 4-Epidemiology and prevention: chronic non-communicable diseases. 5-Communicable diseases: epidemiology...

Epidemiology Dr. Asma Sayedali BDS UofK MD SMSB Course contents 1-Introduction to epidemiology. 2-Measuring health and disease. 3-Causation in epidemiology. 4-Epidemiology and prevention: chronic non-communicable diseases. 5-Communicable diseases: epidemiology surveillance and response. 6-Clinical epidemiology. 7-Environmental and occupational epidemiology. 8-Epidemiology, health policy and planning. What is epidemiology? Epidemiology originates from Hippocrates’ observation more than 2000 years ago that environmental factors influence the occurrence of disease. However, it was not until the nineteenth century that the distribution of disease in specific human population groups was measured to any large extent. This work marked not only the formal beginnings of epidemiology but also some of its most spectacular achievements. The finding by John Snow that the risk of cholera in London was related to the drinking of water supplied by a particular company provides a well-known example. Definition “the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the prevention and control of health problems”. Epidemiologists are concerned not only with death, illness and disability, but also with more positive health states and, most importantly, with the means to improve health. The term “disease” encompasses all un favorable health changes, including injuries and mental health. Scope focus of an epidemiological study is the population defined in geographical or other terms; for example, a specific group of hospital patients or factory workers could be the unit of study. Early studies in epidemiology were concerned with the causes(etiology) of communicable diseases, and such work continues to be essential since it can lead to the identification of preventive methods. In this sense, epidemiology is a basic medical science with the goal of improving the health of populations, and especially the health of the disadvantaged. Causation of disease Although some diseases are caused solely by genetic factors, most result from an interaction between genetic and environmental factors. Diabetes, for example, has both genetic and environmental components. Personal behaviors affect this interplay, and epidemiology is used to study their influence and the effects of preventive interventions through health promotion. Natural history of disease Health status of populations Epidemiology is often used to describe the health status of population groups. Knowledge of the disease burden in populations is essential for health authorities, who seek to use limited resources to the best possible effect by identifying priority health programs for prevention and care. In some specialist areas, such as environmental and occupational epidemiology, the emphasis is on studies of populations with particular types of environmental exposure. Achievements in epidemiology Smallpox The elimination of smallpox contributed greatly to the health and wellbeing of millions of people, particularly in many of the poorest populations. Smallpox illustrates both the achievements and frustrations of modern public health. In the 1790s it was shown that cowpox infection conferred protection against the smallpox virus, yet it took almost 200 years for the benefits of this discovery to be accepted and applied throughout the world. An intensive campaign to eliminate smallpox was coordinated over many years by the World Health Organization (WHO). An understanding of the epidemiology of smallpox was central to its eradication, in particular, by: providing information about the distribution of cases and the model, mechanisms and levels of transmission. mapping outbreaks of the disease. evaluating control measures. The fact that there was no animal host was of critical importance together with the low average number of secondary cases infected by a primary case. When a ten-year eradication program was proposed by WHO in 1967, 10–15 million new cases and 2million deaths were occurring annually in 31 countries. The number of countries reporting cases decreased rapidly in the period 1967–76; by 1976 smallpox was reported from only two countries, and the last naturally-occurring case of smallpox was reported in 1977 in a woman who had been exposed to the virus in a laboratory. Smallpox was declared to be eradicated on 8 May 1980. Several factors contributed to the success of the program: universal political commitment. a definite goal, a precise timetable, well-trained staff and a flexible strategy. Furthermore, the disease had many features that made its elimination possible and an effective heat-stable vaccine was available. In 1979, WHO maintained a stockpile of smallpox vaccines sufficient to vaccinate 200 million people. This stockpile was subsequently reduced to 2.5 million doses, but given renewed concern about smallpox being used as a biological weapon, WHO continues to maintain and ensure adequate vaccine stocks. Epidemiological methods were used to establish the following features of smallpox: there are no non-human hosts. there are no subclinical carriers. recovered patients are immune and cannot transmit the infection, naturally-occurring smallpox does not spread as rapidly as other infectious diseases such as measles or pertussis. transmission is generally via long-lasting human-to-human contact. most patients are bedridden when they become infectious, which limits transmission. Thanks