infection. In 1977, Larson et al. reported that stool specimens commonness of fever, depression and decreased appetite. This from affected patients contained a toxin that produced cytopathic is consistent with recognition in humans that CDI is not always changes in tissue culture cells. C. difficile was identified as accompanied by overt diarrhea, as discussed above. The high the source of the cytotoxin. It is now clear that C. difficile is rate of CDI in 2014 at HEMI neonatal unit resulted in a suspicion responsible for virtually all cases of human pseudomembranous of hospital-associated infection, but preliminary investigation colitis and 20% of the cases of antibiotic-induced colitis. has revealed 7 different ribotypes from nine clinically-affected Pathogenesis of antibiotic-associated diarrhea/colitis begins foals that were tested, something that is consistent with multiple with a disruption of colonization resistance (disruption of the community sources rather than a hospital focus. Farms in Central normal colonic flora) of C. difficile. Colonization occurs by the Kentucky have also experienced outbreaks (>10% incidence) of C. oral-fecal route. C. difficile forms heat-resistant spores that can difficile neonatal enterocolitis within their foaling barns. persist in the environment for years. These spores can survive Diagnosis of C. difficile infection depends on the demonstration the acid environment of the stomach and convert to vegetative of C. difficile toxins in the stool. The cytotoxin assay that uses forms in the colon. Environment contamination by C. difficile tissue cell culture had been the gold standard for diagnosis. It is particularly common in human hospitals that have reported is the most sensitive test (sensitivity 94-100% and specificity isolation rates of 11.7% to 29%. Health care personnel may carry 90%), detecting as little as 10pg of toxin B (This test is not used bacteria on their hands, under rings, or on stethoscopes, but fecal commonly because it is time consuming and expensive). A stool carriage by staff is rare. High rates of infection can be isolated culture of C. difficile is a less efficient method of establishing from stalls (hospital rooms), scales, thermometers and surgical a laboratory diagnosis, since some strains of C. difficile are preparation room. Clostridium difficile has also been implicated nontoxigenic (approximately 25%). Two enzyme immunoassays in an outbreak of colitis among horses at veterinary teaching have been introduced that 1) detect toxin A/toxin B (Clostridium hospitals. difficile TOX A/B test, Techlab®, Blacksburg VA USA ) or 2) detect When established in the colon, pathogenic strains of C. difficile antigen of Clostridium difficile and toxin A (TRIAGE® Micro; produce toxins that cause diarrhea and colitis. Strains that do BIOSITE, San Diego CA 1-888-BIOSITE). These tests have a good not produce toxins are not pathogenic. Two large exotoxins, sensitivity (69-87%) and specificity (99 to 100%). Clostridium toxin A (enterotoxin) and toxin B (cytotoxin) are produced by C. difficile TOX A/B test, Techlab® has been validated for use in feces difficile. Toxins A and B appear to act synergistically which cause of horses. The C. difficile toxins have been found to be stable in fluid secretion, mucosal damage, and intestinal inflammation. fecal samples which were refrigerated at 4˚C for 60 days. DO Toxin A is also a chemoattractant for human neutrophils in vitro. NOT USE STYROFOAM CUPS to submit a fecal sample because Recently, a third toxin, an actin-specific ADP-ribosyltransferase they can bind the toxins. PCR techniques can also be used to (binary toxin), has been identified in certain strains of C. difficile differentiate toxigenic strains from nontoxigenic strains in isolated from human patients. The role and the pathogenesis of feces or among bacterial isolates. However, PCR methods can binary toxin is unclear, but it may act synergistically with toxins detect toxigenic C. difficile organisms that are present in low A and B. The toxic effects appear to follow binding of toxins to and clinically irrelevant levels. A related issue is the accuracy membrane receptors. After binding to its intestinal receptor, of testing in foals. The author has noted an increased number Toxin A enters the cell and alters the actin cytoskeleton, leading of C. difficile enterocolitis cases that have tested positive for the to cell rounding. Toxin B causes the identical rounding. C. difficile glutamate dehydrogenase antigen (a highly sensitive Clinical presentation of C. difficile in foals range from anorexia test that detects the organism) and negative for Toxins A and and pyrexia to fulminate colitis with ileus. The foals with severe B utilizing a commercially available Rapid Membrane Enzyme colitis become anorexic and dehydrated. In addition to the Immunoassay. Results from 2013 and 2014 at HEMI revealed diarrhea, foals become tachypneic, which may be secondary 11.6% (34/291) and 15.6% (71/454), respectively, samples that to discomfort associated with the enteritis, pyrexia, metabolic were antigen positive but toxin negative. This could be caused by acidosis or the anxiety of being in the hospital. Hypoproteinemia a few different reasons, each with different clinical implications. is also a feature of C. difficile secondary to the effects of toxins It could indicate the presence of C. difficile in the absence of A and B leading to extravasation of plasma proteins. Metabolic relevant toxin production. It could also result from sub-optimal acidosis is also consistent with clostridial enterocolitis and sensitivity of the assay. Another possible cause is presence of hypovolemia or gastrointestinal tract loss of bicarbonate. high levels of toxin in the proximal intestinal tract with disease Hyponatremia may also be attributable to the gastrointestinal at that location (e.g. accounting for fever and colic) but little toxin tract losses, as well as to an excess of free water associated with in feces. It could also result from the presence of strains that are water consumption by these foals. nontoxigenic (and therefore clinically irrelevant). Understanding In Kentucky, there has been recognition of an increased which of these occur is critical because of the marked differences incidence of C. difficile infection (CDI) in the equine community in clinical relevance of test results in those situations. Pilot over the past several years, with increased disease on farms study of discrepant results has been performed. In 10 antigen and an increase in the number of foals arriving to a hospital positive, toxin negative cases, enrichment culture for C. difficile setting without enteric disease that later develop clinical disease was performed, and C. difficile that possessed genes encoding (e.g. pyrexia, leucopenia and colic) usually after 48 hours of toxins A and B genes were isolated in 9 (90%). A separate subset hospitalization. CDI is often subtle initially and not consistent of 30 antigen-positive/toxin-negative samples were submitted for with classical CDI, with a lower incidence of overt diarrhea but commercial PCR for Toxin A and B genes, with 74% (22/30) being
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The Practitioner 29