The prevalence and prevalence of diseases, infectious and non-infectious, also affect epidemiology. New infectious diseases such as HIV infection have emerged in low-income countries. Nevertheless, the prevalence of these infectious diseases has decreased over time. Infectious diseases still exist in low-income countries [78], but the incidence of chronic diseases is increasing [79]. Epidemiological definitions have evolved in this direction, with a decrease in the presence of terms for infectious diseases. Epidemiology and the social sciences converge most completely in research on social stress and health. Hypotheses linking stress and health were generated (not exclusively, but very importantly) from observations on social inequalities, social integration and health. Basic socio-epidemiological research has shown almost conclusively that associations of these factors are not an artifact of research design. When subjected to the most rigorous forward plans that include relevant control variables from other domains (e.g. other risk factors, access to health care and nutrition), social inequality and social integration independently contribute to disease risk. Often referred to as the «gold standard» for scientific evidence, human experiments are often impractical and unethical for studying the effects of exposure to potentially toxic environmental influences. Animal and in vitro experiments make an invaluable contribution to the assessment of environmental health risks, but differences in toxicokinetics and toxicodynamics between animal species, the use of genetically homogeneous test populations, and unrepresentative exposure scenarios pose a challenge for extrapolation to humans.

Environmental epidemiology helps address these challenges; It is a systematic approach to collecting data observed by events occurring in defined populations, called «natural experiments». As a first example, Dr. John Snow identified the consumption of contaminated drinking water as the cause of a virulent cholera epidemic in London in 1854. In conjunction with environmental toxicology, environmental epidemiology makes a critical contribution to the assessment of risks to human health and the design of interventions to protect human health. Clinical epidemiology has not been without its critics, especially among more traditional epidemiology departments, which have (often rightly) perceived their loss of resources and bright young minds for this new discipline. For example, in 1983, Walter Holland advocated the complete abandonment of the concept of clinical epidemiology. While acknowledging its usefulness over the past 15 years, he found it to be a divisive term that only gave «seriousness» to epidemiologists who practised medicine, giving the impression that one form of education (using epidemiology to solve clinical problems) was more appropriate than another (mastering classical epidemiological methods) and shaped students` perceptions of societal priorities and needs. In response to his criticisms, it was suggested that the distinction between clinical and nonclinical epidemiologists was nominal and not ordinal, but that his other criticisms were not only true, but also welcome: clinical epidemiology was a better way to teach medical students, and clinical epidemiology changed the perception not only of medical students (who began to consider them as basic sciences). relevant), but entire faculties (departments of clinical epidemiology).

increase in number and size; Clinical departments conducted more and better «clinical» practical research), and learned societies recognized the relevance of clinical epidemiology to «clinical research» in ways that classical epidemiology could not achieve (Sackett, 1984). The field of epidemiology is highly interdisciplinary. In addition to its close connection with statistics, especially biostatistics, it draws heavily on concepts, knowledge and theories from disciplines such as biology, pathology and physiology in the health and biomedical sciences, as well as the disciplines of anthropology, psychology and sociology in the behavioral and social sciences. At the same time, from the point of view of refined social theory, the concepts of social inequality and social integration are rather blunt instruments; None of these concepts specify very well the exact types of social processes that influence disease risk in individuals. In 1976, an influential paper emerged that provided a conceptual basis for the work in progress and for the work that would follow over the next 2 decades. John Cassel, an epidemiologist, has been critical of conventional epidemiological models for more than 20 years, saying a narrow focus on biological risk factors has led researchers to ignore the extent to which social factors affect groups` risk status. This criticism bore fruit in 1976 with his essay «The Contribution of the Social Environment to Host Resistance». The key concept here, host resistance, is a brilliant rhetorical appeal to the fundamental ideas of basic infectious disease epidemiology. In the classical Triassic-host environment, agent and host interaction in a given environment does not automatically lead to host disease; Rather, there are factors (e.g., nutritional status) that allow the host to resist the penetration of a pathogen. Cassel made the analogy with human social life. Individuals are exposed to certain types of stressful events and circumstances, often due to their disadvantage in the socio-economic hierarchy.

However, there are resources that individuals can use to resist these psychosocially harmful events and circumstances, resources that are social in nature. Greater social inclusion can give individuals a greater chance to receive help and support from others in times of crisis, as well as their emotional support. This support, says Cassel, «cushions» the impact of social stressors on disease risk. By buffering, Cassel means that under conditions of low support from others, increased exposure to stressors is associated with a significant increase in disease risk, but that under conditions of high social support, increased exposure to stressors has little association with health outcomes. This protects people with better access to social support from the harmful effects of stressors. One of the first great figures in the historical development of epidemiology was the ancient Greek physician Hippocrates, traditionally considered the father of medicine. Hippocrates is believed to have written Epidemics and On Air, Water, and Places, works in which he tried to explain the onset of diseases on a rational rather than supernatural basis. Hippocrates recognized disease both as a mass phenomenon and as a phenomenon that affects individuals. The distribution of concepts by frequency is as follows: health (12/30); population (18/30); illness (27/30); Study (19/30); Distribution (16/30). This distribution is almost that of the definition of epidemiology in books.

Epidemiology was associated with statistics in 6% (4/69) of definitions [3, 30, 32, 52]. Definitions of online dictionary pages, encyclopedias such as Wikipedia or student websites have also been retained, using the above strategy (keywords: (definition AND epidemiology) OR (epidemiology definition)). In 1979, Evans [3] analyzed the content of the definitions used by Lilienfeld to create his definition of epidemiology. In summary, he identified 23 different terms and concepts. For each term and concept, the frequency of occurrence in the definitions was calculated. Then they were divided into eight categories: status of the person (disease, infectious disease, physiological conditions, injuries, health); the group affected (populations, community, mass phenomena, epidemic); distribution of the disease; propagation (spread, spread, dynamics); incidence, occurrence; etiology (causes, determinants, circumstances of occurrence, ecology); understanding of diseases (natural or natural history, understanding of the process); Prevention and control.