1. INTRODUCTIONEpidemiology, a basic health science, is characterized by concepts that are defined by specific terms (terminology), principles, methods and topics that have varied over time under the influence of demographic, cultural, social, and economic factors, among others. However, knowledge advances and new problems arise. Accordingly, epidemiology, like other scientific areas, is facing new challenges and must evolve. As Richard Doll put it, “Classical methods of epidemiological research are proving less and less productive as the simple problems are being successfully solved. They will doubtless continue to be used to make new discoveries from time to time… but without some brilliant new inspirations, the rate of discovery of new facts of any importance by the use of these classical methods must be expected to slow down”.
Recently, Saracco R (2010) identified four challenges: the challenge of the evolution of biology, the challenge of the evolution of the environment, the challenge of the evolution of society, and the challenge of diversification versus integration[1]. In the latter challenge, a methodological axis can be identified, for example, developments in the area of measurement of exposures and of measurement errors, of methods in genetic epidemiology, etc. A second axis is the diversification of fields of interest, for example, cancer epidemiology, ageing epidemiology, etc. Another axis of diversification is the separation between those who specialize in aspects of research and those who define plans and implement interventions, like in clinical medicine, with its variety of specialists or "sub-experts" in technical performance, be it in the field of diagnosis or therapy. Another area of specialization is clinical epidemiology.
2. CLINICAL EPIDEMIOLOGY
Concept
These terms correspond to the application of principles and epidemiological methods and statistical techniques to the study of clinical problems and improvement of patient care. Therefore, it is "clinical," because it seeks to answer clinical questions and help make clinical decisions informed by the best available evidence. It is epidemiological, because many of the methods used to answer these questions were developed by epidemiologists, and because the care given to individual patients is seen in the context of a larger group of people the patient is part of.
Fields of interest
The main objectives of clinical epidemiology are: definitions of normality and abnormality (is the individual ill or not? What is the value of a health-related measurement that is associated with disease or from which treatment is justified?); validity of diagnostic tests (what is the accuracy and validity of the diagnostic tests used?); natural history and prognosis of diseases (what are the consequences of untreated disease progression versus the clinical course of disease under treatment?) effectiveness of the treatment (what is the effect of treatment on the clinical course of the disease?); prevention in clinical practice (what interventions are associated with decreased incidence of the disease?, does early diagnosis and treatment improve the course of the disease?). However, etiology is also one of the main areas of interest of clinical epidemiology, although it is already a primary goal of epidemiology (what factors cause the disease?), in addition to the analysis of risks and benefits of diagnostic and therapeutic procedures (cost-effectiveness analysis, decision analysis) and to the evaluation of health care services. Indeed, health care research can be very useful for care provision (management, recommendations, best practices, etc.).
Epidemiological research
The growing awareness of the importance of probability inference with regard to diagnosis, treatment and prognosis of individual patients, justifies the increased interest in approaches to epidemiological research as a means to enhance clinical medicine. However, as a basic principle, in most clinical situations the diagnosis, prognosis and treatment outcomes are uncertain for an individual. Therefore, a prediction should be expressed as a probability, estimated by the experience with identical patient groups or populations. On the other hand, at a time when the costs of health care are increasing, clinical practice and the improvement of clinical outcomes (effectiveness and efficiency) depend on the application of Clinical Guidelines (NOCs) based on evidence (Guidelines). These recommendations are much determined by the results of studies evaluating diagnostic procedures, treatment and prognosis. In turn, these studies result from partnerships (multidisciplinary teams) consisting mainly of clinicians, epidemiologists, bio-statisticians, representatives of institutions/regulatory bodies, representatives from health associations, and health economists [2].
Study designs
Although all classic designs of epidemiological research may be present in clinical discussions, their delineation may be very different from the one set for epidemiology etiology [3]. For example, case-control studies are used to define the different characteristics of a diagnostic test with regard to the gold standard (sensitivity, specificity, accuracy, etc.), not to identify associations by odds ratio. In the context of screening and prevention, research based on case-control observational studies is an ongoing challenge that involves several issues. Without wishing to discuss the multiple components of a screening programme and technical decisions, the following are important topics: the target of the screening - a disease of low prevalence and at a preclinical phase, the problems arising from the risks and benefits of screening; the test used in the screening - sensitivity and specificity relationships; the pattern of events after the screening; the effectiveness of the screening and cost-effectiveness analysis.
Prognosis studies are naturally cohort studies, preferably from the first event (inception cohort), but with survival analysis methods (Kaplan-Meier curves and cumulative incidence curves), identification of risk factors in the evolution of the disease (prognosis), probability of events over time, censored data, etc. However, prognostic factors are characteristic of the disease (i.e. tumour staging, degree of stenosis or location of atherosclerotic lesions) or of the treatment (drug type and/or dosage, medication regime). Cross-sectional studies are frequently used in clinical epidemiology, not to study prevalence, but to compare clinical measures and to evaluate the association between measurement and the stage of the disease (i.e. diagnosis in case-control analysis). Clinical trials are rarely addressed in etiological epidemiology courses, but justify a particular emphasis in clinical epidemiology courses because they are very important to guide decisions in terms of treatment, screening and prevention. In most cases they are experimental, multi-centred studies, a special type of cohort study, which is developed using a rigorous and detailed procedure that involves randomization of the intervention-exposure groups (each treatment group) and concealment, in a rigorous follow-up informed by systematic records of pre-defined clinical parameters. On the subject of clinical trials, both those that are designed to demonstrate superior efficacy, which are the majority, and the tests for equivalence or noninferiority, it is important to discuss other topics: internal and external validity (generalization), subgroup analysis, meta-analysis, hierarchy of scientific evidence, and guidelines for clinical practice. Molecular and genetic methods have been used in clinical epidemiology in the areas mentioned earlier of diagnostic, screening, risk stratification, prognosis, and choice of treatment (pharmacogenetics). It is an area of research from which many contributions to health are expected, and whose implementation requires skills and interdisciplinary effort.
3. EPIDEMIOLOGY AND CLINICAL PRACTICE
Evidence Based Medicine (EBM) is a modern name for the application of epidemiology to clinical patient care, using formal methods to characterize evidence over the results of medical interventions. It is, nonetheless, the integration of individual clinical expertise with the best available external evidence and which has its origins in systematic search. It is based on the application of the scientific method to all medical practice, i.e., it corresponds to the "conscientious, explicit and judicious use of current best evidence." This approach applies at the level of clinical care, management/administration and political decision[2]. Despite the initial reluctance of some physicians with regard to the introduction of clinical epidemiology, medical education and literature recognize the value that science can offer to clinical medicine [4]. Currently, epidemiology cannot be seen as a mere instrument, since it is a scientific interdisciplinary discipline which, in translational research and in partnership with clinical medicine and other sciences, sectors and organizations, is essential to meet the challenges posed by the health sector[5]. In this sense, it is important that epidemiological thought and epidemiological research are seen as an evolving process to which different types of study, often descriptive, can be applied, depending on the issues under study. In the field of clinical epidemiology, research in the areas of diagnosis, prognosis and therapy continue to be necessary, as they constitute important objectives to help improve patient care, and are essential to help set guidelines/Clinical Practice Norms, and normative precepts that are determinant for medical performance, i.e. medical ethics. Epidemiology is well established as a key support to the process of decision making, now and in the future.
Evangelista Rocha
Evangelista Rocha – Institute of Preventive Medicine of the Faculty of Medicine of the University of Lisbon (FMUL)
Guest Auxiliary Professor at FMUL
evangelistarocha@hotmail.com
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Bibliography:
1. Saracci R., Introducing the history of epidemiology. In: Olsen J, Saracci R, Trichopoulos D, editores. Teaching Epidemiology – a guide for teachers in epidemiology, public health and clinical medicine. Oxford: Oxford University Press; 2010.
2. R Andreia, Bugalho A, Carneiro AV. Manual de Elaboração, Disseminação e Implementação de Normas de Orientação Clínica. Manual de NOCs CEMBE 2007. Centro de Estudos de Medicina Baseada na Evidência. Faculdade de Medicina de Lisboa.
3. Rocha E. Investigação epidemiológica: Uma visão geral. Revista Factores de Risco 2007; 4 (Ano 2): 64-68.
4. Rocha E, Miguel JMP. A importância da investigação epidemiológica. Rev. Port. Cardiol. 1997; 16(9): 667-71.
5. Barros H. Evolução do Pensamento Epidemiológico – O Ser de uma Disciplina. Arquivos de Medicina 2006; 20 (4): 121-5.
