Subject, theory, methods and tasks ofPresentation Transcript
Subject, Theory, Methods and Tasks of Epidemiology Prof. Dr. N. Ribarova, MD
Medical science as a whole encompasses a great number of formal sciences which are estimated in two major trends, prophylaxis and therapy, depending on their subjects and aims.
Prophylactic disciplines have as their subject to study healthy man , and their aim is to preserve human health by studying the causes of diseases and their terms of emergence as well as the ways of preventing them.
Epidemiology is one of the main disciplines in this group.
The development of epidemiology of infectious diseases during the centuries have been governed by public health needs.
The definition of epidemiology as a science in various historical periods has relied on the relative authenticity of social phenomena and processes.
Till the middle of XX century many authors define epidemiology as a science for study and fight against epidemic diseases.
Progress in infectology later defines it as a science of the epidemic process ; most recently, it has been noted that this definition does not reveal its essence as well.
WHO – 1960 – Prague:
Epidemiology is an independent trend of medical science studying the causes for the emergence and dissemination of infectious diseases in human society and applying thus gained knowledge for fight against, restriction and, eventually, complete eradication of these diseases.
Epidemiology is a scientific area studying infectious diseases in respect to evolution and ecology as well as in relation to antiepidemic and prophylactic issues; it studies their biosocial nature and dependence on social and natural factors.
Epidemiology realizes various aims including elimination and liquidation of infectious diseases as well.
Epidemiology of infectious diseases is a scientific area with broad frames of knowledge in the field of existence, occurrence and disappearance of parasitic pathology in human society.
Epidemiology of infectious diseases , as a separate medical science, is a fundamental science within prophylactic medicine because it studies and offers prophylactic measures for mass diseases. It has one of the basic activities in medical science and practice.
Subject of Epidemiology
At the current stage of development of knowledge, the subject of epidemiology is defined as the state of interactions between a microorganism and a microorganism on individual and population level, at specific social and ecosystemic conditions – or the epidemic process , notwithstanding the theories of many authors specifying a series of forms, states, and factors in the development of infectious diseases in human society which do not find their place within the definition of epidemic process.
Theory of Epidemiology
As any independent medical science, epidemiology has its theory. Having been developed in the course of historical and logical development of knowledge, it encompasses the following trends:
Principles of epidemic process;
Principles of infectious process;
Theory of immunity and use of specific immunoprophylaxis;
Principles of natural focal diseases;
Theory of elimination and liquidation of infectious diseases;
Theory of the systemic character of epidemic process and systemic approach for its study and prevention;
Scientific system of epidemic surveillance and control of infectious diseases;
Scientific system of infectious diseases prevention;
Organizational foundations of the activities for infectious diseases prevention and control;
Aim of Epidemiology
To study the laws and dissemination of infectious diseases; to organize the epidemiological practice of the entire society for their restriction, prevention of complications, reduction of economic and social damages and, in the final account, elimination and liquidation of these diseases.
Goals of the epidemiology
To explain theoretically the causes for arising, development and expirerius of the epidemical processes.
To create and apply effective means and methods for control of the infectious diseases.
To create and apply effective means and methods for prevention of infectious diseases, encluding their elimination and liquidation.
History of Epidemiology
Without studying the history of the subject of a science, a theory of the discipline and logical reflection of the nature of the processes in the different stages of its development cannot exist.
The historical development of knowledge on epidemiology has progressively enriched its theory.
Stages of development of the knowledge on the epidemiology of infectious diseases:
Empirical speculations on the contagiousness of infectious diseases;
Enrichment of the knowledge on the causes, emergence and dissemination of epidemic diseases and enlargement of the empirical measures to fight these diseases;
Emergence and disappearance of an infectious disease during the Middle Ages;
Confirmation of the principles of the contagiousness of infectious diseases. Beginning of specific vaccine prophylaxis;
Development of bacteriology and the theory of special epidemiology;
Empirical data showing alterations in the severity of the course of infectious diseases;
Emergence of the idea for a public stand on the fight against infectious diseases;
Establishment of the principles of epidemic process;
Implementation of the program for eradication of malaria in the 1950s;
Molecular epidemiology: molecular-biological and molecular-genetic methods for diagnosing infectious diseases
Method of Epidemiology
The epidemiological method is an aggregate of methodological know‑how – observation, historical and geographical description, juxtaposition, statistical analysis, diagnostic methods designed to characterize the epidemic process as well as to substantiate the measures for prevention and control of infectious diseases and to estimate their effectiveness.
The method is specific for the epidemiology of infectious diseases because it studies the triad:
parasite – in biological, ecological and epidemiological aspect;
macroorganism – reaction during the encounter with the parasite;
environment – in all its aspects with the aim to develop and apply prophylactic programs for liquidation and elimination of infectious diseases.
Parts of the epidemiological method:
1. Universal part:
Definition of the problem;
Collection, classification and analysis of the information;
Formulation of a hypothesis and determination of the hypotheses subject to testing;
Testing the formulated hypothesis – through prospective and longitudinal studies;
Determination of specific factors leading to emergence of a particular disease in the group of highly exposed individuals;
Conclusions and subsequent control and preventive measures. Estimation and testing their effectiveness.
2. Specific part:
Studying the biology, ecology and immunology of the specific etiological agent;
Studying the epidemiology of the infectious disease;
Creation of a scientific theory of the nature of the infectious disease and the fight against such a disease;
Setting up a program for prevention;
Practical application of the program for prevention and acquisition of the assigned aim.
The logical sequence of know-how skills utilized by the epidemiological approach helps to the formulation of the following methods:
Aim – to determine the incidence of the disease, the risk factors and its medicosocial significance and to formulate the hypothesis for the possible prevention and control measures.
Baseline data: the registered and reported materials and the results from the representative studies.
The registered and reported materials are characterized by accessibility and ease of collection.
The representative studies are more precise but more complex for performance.
Representativeness is a variable determined by means of an estimation of the variation series.
Variants of representative studies utilized in the epidemiology
Individual selection Cluster selection Stratified selection Method of forming representativeness Single-point (cross-section) study. Long-term (longitudinal, prospective) study Time of performance Variants Signs
Parameters of the descriptive method:
Incidence – the ratio between the number of newly registered individuals with an infectious disease for a specified period of time and the individuals at risk of developing the disease during the same period in % 000 .
Prevalence – the ratio between the number of cases with an infectious disease (newly registered and old cases) at a definite point of time and the magnitude of the population at risk at the same point in % 0 .
Mortality – the ratio between the number of deaths for a specified period and the number of individuals at risk of death for the same period x 100 000.
Lethality – the ratio between the number of individuals deceased from a particular disease for a specified period and the number of diseased individuals during the same period in %.
Incidence in respect to particular variables:
* gender, education, socioeconomic status;
* territorial characterization;
* isolated microorganisms;
* seasonal variations;
* focal variations;
* index of effectiveness of the measures.
In the epidemiological studies, all available to medical statistics generally accepted statistical parameters are utilized:
- absolute values (numbers);
- intensive parameters;
- average values;
- extensive parameters;
- cumulative data;
- relative values;
- ratio parameters;
- standardized parameters.
The reliability of statistical parameters and the relation among the studies epidemiological events is subject to estimation. Leveling of dynamic series and estimation of the direction and occurrence of trends is performed.
Descriptive epidemiology is occupied with collection of data for the health status of the population and its change over time with the aim to establish the foundation for organizational measures, planning and management of medical aid as well as formulation of hypotheses on possible cause-effect relations.
The descriptive method of epidemiology is used for analyzing the characteristic features of the distribution of the incidence of a specific nosological entity according to territory among various social and age populations and specific groups, and according to time (multi-annual and annual dynamics, cyclic and seasonal variations) expressed in intensive parameters.
The formulation of the hypothesis for the risk factors utilizes logical methods to discover causal relations . Quantitative methods are used for statistical estimation of the relations between epidemiological phenomena. This method does not clarify the character of these relations which is done through the analytical method.
It discovers the causal relation between the disease and the external factors; it estimates and confirms the hypothesis for the risk factors causing the emergence of the problems discovered with the help of the descriptive epidemiological method; it forms the theory of epidemiology and the prevention of diseases.
Major analytical trends of research are:
Cohort study – an analytical research study in which the groups of individuals are defined on the basis of the presence or absence of exposure to a probable risk factor, and subsequently the groups are compared in relation to the proportions within these groups who have developed the studied disease.
Case-control study – a type of analytical research study in which subjects are selected on the basis of whether they have (case) or have not (control) a particular disease. Subsequently the groups are compared in relation to the proportions within these groups who have been exposed to a specific risk factor.
It is applied only in cases of controlled reduction of exposition.
Experimental epidemiology is closely related with primary prevention of the disease. In many cases, the setting up of a program for prevention is much more a question of applying existing knowledge than gathering new information.
Experimental epidemiological studies can be performed with a group of individuals where a suspected factor is influenced by means of various diagnostic, therapeutic and prophylactic interventions, and the effect of their influence is compared among 2 or more experimental and control groups.
During the last decades, epidemiological models have been developed to be used for the study of the natural course of the epidemic process in a particular disease as well as for the study of the perspectives of prevention and control in view of the elimination and liquidation of infectious diseases.