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  • Understand the important contributions of chance, bias, and confounding as potential sources of false epidemiologic associations and apply methods to control for these factors
  • Describe commonly used measures of morbidity and mortality as they are used in the global setting
  • Discuss the various types of epidemiologic study designs together with their relative strengths and weaknesses as well as the measures of association they provide
  • Interpret test results within the context of screening and surveillance with attention to sensitivity, specificity, and predictive value
  • Apply epidemiologic methods to the control of infectious disease
  • Distinguish the two types of surveillance and describe the components of a useful surveillance program

Epidemiology is concerned with the identification, measurement, and analysis of factors that may be associated with differences in the health status of populations. The goal of such investigations is to modify these factors to improve the health status of individuals. Classical epidemiology is focused on populations, seeks to identify risk factors, and has been described as the “basic science” of public health. Therefore, some familiarity with epidemiologic methods is essential to the understanding of public and global health. The public health approach can be illustrated by the epidemiologic triad as applied to malaria (Figure 3-1).

Figure 3-1.

Epidemiologic triad for malaria.

According to this model, disease arises through interactions between a host, environment, and agent. In the case of many infectious diseases, a vector through which the agent is transmitted is also relevant. This model allows opportunities for the interruption of disease transmission to be clarified. For example, in the case of malaria, opportunities might include the use of insecticide-treated bednets for the host, reduced areas of standing water in the environment, destruction of the Anopheles mosquito vector through pesticides, and chemoprophylaxis targeted at the plasmodium.

Note that the public health model takes a very broad view of what constitutes a risk factor for disease. Whereas a traditional biomedical paradigm tends to focus on a small number of causes for a disease, such as a specific microorganism, public health considers more diverse social, economic, and environmental factors as playing a potentially causative role in disease development, each offering an opportunity for intervention.

Indeed, there are potentially an infinite number of causative factors, each acting at various points along a timeline as shown in Figure 3-2, which depicts two such factors for simplicity. For each factor, there is an induction period between when that factor acts and when the disease is initiated. After disease initiation, there follows a latent period corresponding to a preclinical phase before the disease is recognized. Preventive strategies can be placed into three groups based on this chronology. The preferred approach is always primary prevention because interventions are made prior to disease initiation, such as vaccination to confer immunity to measles. Screening is by definition a form of secondary prevention...

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