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Although not all infectious diseases require diagnostic laboratory testing, clinicians often rely on laboratory tests to help identify a causative agent, select an appropriate antimicrobial agent, and/or assess response to therapy. Children are more susceptible than adults to certain infections such as viral respiratory infections, streptococcal pharyngitis, and otitis media. The variety of potential pathogens and difficulties in collection of specimens create diagnostic challenges that are specific to children. Ordering the right test at the right time is paramount for laboratory diagnosis of infectious diseases and for preventing false-positive and false-negative results. Therefore, it is important that clinicians have a basic understanding of diagnostic microbiology so that they collect the optimal specimen and order the most appropriate test for diagnosing and selecting the most appropriate therapy for the infectious process.
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COLLECTING AND PROCESSING BACTERIAL CULTURES
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No test methodology or degree of laboratory expertise can correct the error of inappropriately collected and transported specimens. The proper collection and handling of clinical specimens is as important as selecting the correct medication for treatment. Common problems with clinical specimen collection and handling include insufficient quantity, contamination, inappropriate transport conditions, and delay in transport to the laboratory. Swabs, although commonly used, are less likely to yield reliable results, and their use for obtaining bacterial cultures should be discouraged, except when submitted for throat culture (or for rapid antigen tests, which include swabs as part of the test kit). Submission of sterile body fluid, scrapings, biopsy, or tissue samples increases the chance of recovery of pathogens and reduces the isolation of contaminants that may mislead or result in misdiagnosis. Table 221-1 provides important and useful tips for collection of specific specimens.
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