Gastrointestinal pathogens profoundly affect human health and well being. The provider's ability to render optimal care often highly depends on diagnostic microbiologic support. We aim to provide a clinically pertinent assessment of the current state of our ability to diagnose human gastrointestinal pathogens and describe (and decry) the unsophistication of many current diagnostic methods and strategies.
Recent advances involve improved stool polymerase chain reaction assays and application of this technology to a broader panel of pathogens, stool antigen assays, and improved culture techniques, but there is little penetration of such diagnostic advances into clinical practice. Many such techniques remain limited to research or epidemiologic use and are not typically available in the clinical laboratory.
Multiple clinical and laboratory factors need to be considered when attempting to diagnose the wide variety of gastrointestinal pathogens afflicting humans. Careful interpretation of diagnostic tests with attention to the population studied and the characteristics of each test is necessary.
[Show abstract][Hide abstract] ABSTRACT: Acute bloody diarrhea should be considered a medical emergency. Its causes are frequently serious or actionable or both and are usually identified. However, acute bloody diarrhea as a stand-alone clinical presentation has received little scholarly attention in the past several decades. Although the range of possible causes of acute bloody diarrhea is broad, infectious considerations are paramount and should always be prioritized in the evaluation of such patients. History, examination, and laboratory testing should be focused on minimizing time to diagnosis (and, by extension, to implementing appropriate therapy). Strategically chosen tests and imaging, avoidance of extraneous diagnostic pursuits, and provision of supportive care while awaiting diagnostic clarity are central to the adroit management of patients with acute bloody diarrhea. Diagnostic considerations differ somewhat between adults and children but have many elements in common, including the need for vigilance in detecting Escherichia coli O157:H7 infection. In this review, we discuss diagnostic approaches (emphasizing the importance of rapid, accurate, and thorough microbiologic investigation) and measures that can be taken to support patients while awaiting information that determines the cause of their disease. These topics are discussed in the context of the medical care that is available to children and adults with bloody diarrhea in most institutions in developed nations.
[Show abstract][Hide abstract] ABSTRACT: We evaluated the performance and cost-effectiveness of a matrix-assisted laser desorption ionization time-of-flight mass spectrometry-based Biotyper system for the routine identification of common enteric bacterial pathogens seen in middle Tennessee from suspicious colonies grown on selective stool culture media. A total of 304 suspicious colonies were selected and further identified from 605 stool specimens. The suspicious colonies were analyzed by the Biotyper system, and the results were compared to those from routine phenotypic methods, which identified 22 Salmonella species, 39 Shigella species, 3 enterohemorrhagic Escherichia coli (EHEC) isolates, 2 Yersinia enterocolitica isolates, 2 Campylobacter species, and 236 gastrointestinal normal flora isolates. The Biotyper system correctly identified the Salmonella species, Yersinia enterocolitica, and Campylobacter species but failed to distinguish the Shigella species and EHEC isolates from E. coli. Among the 236 normal flora isolates, 233 (98.7%) and 228 (96.6%) agreed at the genus and species levels, respectively, between the phenotypic and Biotyper methods. Organism identification scores were insignificantly different between colonies directly from selective media and subsequently from pure subculture. The entire Biotyper identification procedure, from smear preparation to final result reporting, can be completed within 30 min. The Biotyper system provides a rapid and simple screening tool for identifying many, but not all, suspicious colonies grown on selective media within 24 h after inoculation, which shortens test turnaround time by 2 to 3 days.
[Show abstract][Hide abstract] ABSTRACT: Shiga toxin-producing Escherichia coli (STEC) are a leading cause of bacterial enteric infections in the United States. Prompt laboratory identification of STEC strains is essential for detecting new and emerging serotypes, for effective and timely outbreak responses and control measures, for monitoring trends in disease epidemiology, and to ensure accurate diagnosis and treatment. Guidelines for laboratory identification of STEC infections by clinical laboratories were published in 2006 and 2009 (CDC, MMWR Morb. Mortal. Wkly. Rep. 55:1042-1045, 2006; MMWR Recomm. Rep. 58[RR-12], 1–14, 2009). We summarize these recent recommendations for STEC testing by clinical laboratories to emphasize the recommendation that all stools submitted for routine testing from patients with acute community-acquired diarrhea (regardless of patient age, season of the year, or presence or absence of blood in the stool) be simultaneously cultured for E. coli O157:H7 (O157 STEC) and tested with an assay that detects Shiga toxins to detect non-O157 STEC.
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