Specimen collection and transportation are critical considerations, because any results the laboratory generates is limited by the quality of the spedmen and its condition on arrival in the laboratory. Specimens should be obtained to predude or minimize the possibility of introducing extraneous (contaminating) microorganisms that are not involved in the infectious process. This is a particular problem, for example, in specimens collected from mucous membranes that are already colonized with microorganisms that are part of an individual's endogenous or "normal" flora; these organisms are usually contaminants but may also be opportunistic pathogens. For example, the throats of hospitalized patients on ventilators may frequently be colonized with Klebsiella pneumoniae; although K. pneumoniae is not usually involved in cases of community-acquired pneumonia, it can cause a hospital-acquired respiratory infection in this subset of patients. Use of spedal techniques that bypass areas containing normal flora when this is feasible (e.g., covered brush bronchoscopy in critically ill patients with pneumonia) prevents many problems assoaated with false-positive results. likewise, careful skin preparation before procedures such as blood cultures and spinal- taps decreases the chance that organisms normally present on the skin will contaminate the spedmen.
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