Outbreaks of infectious diseases often result from exposure to a common source of the etiologic agent. Generally, the etiologic agent involved in an outbreak of disease is derived from a single cell whose progeny are genetically identical or closely related to the source organism. In epidemiological terms, the organisms involved in the outbreak are clonally related; that is, they have a common origin. Clonally related organisms are members of the same species that share virulence factors, biochemical properties, and genomic characteristics. However, there is sufficient diversity at the species level that organisms isolated at different times and in different geographical areas may be differentiated or classified into subtypes or strains.
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The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.