In response to the questions of epidemiology. Here is a brief explanation on the why, what, and how’s behind the science.
What is epidemiology?
Epidemiology provides the scientific basis of public health through description, quantification, and analysis of patterns of health and disease in populations and includes the study of biological, environmental, behavioral, and social factors underlying disease and health patterns. Such analyses lead to identification of the underlying causes of disease, the planning and evaluation of health services delivery, and the development of intervention strategies, programs, and policies to prevent disease and promote health.
Here it is presented in a different manner.
Epidemiology is the study of diseases in populations of humans or other animals, specifically how, when and where they occur.
Epidemiologists attempt to determine what factors are associated with diseases (risk factors), and what factors may protect people or animals against disease (protective factors). The science of epidemiology was first developed to discover and understand possible causes of contagious diseases like smallpox, typhoid and polio among humans. It has expanded to include the study of factors associated with non-transmissible diseases like cancer, and of poisonings caused by environmental agents.
Epidemiological studies can never prove causation; that is, it cannot prove that a specific risk factor actually causes the disease being studied. Epidemiological evidence can only show that this risk factor is associated (correlated) with a higher incidence of disease in the population exposed to that risk factor. The higher the correlation the more certain the association, but it cannot prove the causation.
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The first step in an epidemiological study is to strictly define exactly what requirements must be met in order to classify someone as a “case.” This seems relatively easy, and often is in instances where the outcome is either there or not there (a person is dead or alive). In other instances it can be very difficult, particularly if the experts disagree about the classification of the disease. This happens often with the diagnosis of particular types of cancer. In addition, it is necessary to verify that reported cases actually are cases, particularly when the survey relies on personal reports and recollections about the disease made by a variety of individuals
(This is where the case definitions of possible, probable, and confirmed become part of the process.)
For Infectious diseases, the science of epidemiology is applied by looking at all the common factors between patients to make informed decisions on the care of the patient, identify a possible source, to limit the spread, to assess the incidence, and provide interventions to decrease the spread and protect public health.
This is over-simplified, and explains the purpose of epidemiology, but it is important to know for the next step. (below)
Here is how clinicians use a systematic approach in identifying (almost any) disease.
Differential diagnosis is the method by which the clinician considers the possible causes of a patient’s clinical findings before making a final diagnosis. [2] [3] Experienced clinicians often group the findings into meaningful clusters, summarized in brief phrases about the symptom, body location or organ system involved, such as “generalized pruritis”, “painless jaundice” and “constitutional symptoms” . . . .
We call these clusters ‘clinical problems’, [3] [4] and include problems of biologic, psychologic or sociologic origin. [5] It is for these clinical problems, rather than for the final diagnosis, that the clinician selects a patient’s differential diagnosis.
(Do not confuse this description of “Clusters” with the common use of the word “cluster” used on this board; they are essentially the same)
Definition of Cluster
Cluster: In epidemiology, an aggregation of cases of a disease or another health-related condition, such as a cancer or birth defect, closely grouped in time and place. The number of cases in the cluster may or may not exceed the expected number. This is determined by cluster analysis, a set of statistical methods used to analyze clusters.
(Clusters are part of the definition in the epidemiological survey. They are specifically defined with parameters, such as in this example.)
A cluster of cases was defined as the occurrence of more than one case among persons presenting an epidemiological link. . . .
Hope that provides some clarification on the study of epidemiology, and why it is so important to monitor all cases reported, confirmed, probable, and possible.
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