Evaluation of the clinical usefulness of C. difficile toxin testing in hospitalized patients with diarrhea

Effective utilization of evolving methods for the laboratory diagnosis of Clostridium difficile infection

Physicians should understand the performance characteristics of evolving laboratory tests used to diagnose Clostridium difficile infection if they are to correctly integrate test results with clinical information and formulate an appropriate therapeutic intervention for patients with antibiotic-associated diarrhea.

Antibiotic-associated bloody diarrhea in infants: clinical, endoscopic, and histopathologic profiles

OBJECTIVE

Antibiotic-associated diarrhea constitutes 1 of the most frequent side effects of antimicrobial therapy with widely varying clinical presentations; however, little is known about its antibiotic-associated bloody diarrhea (AABD) form, particularly in very young children. The aim of this study was to describe the clinical, endoscopic, and histopathologic profiles of community-acquired AABD in infants.

PATIENTS AND METHODS

The study included 23 infants referred with bloody diarrhea that developed a few days after receiving antibiotics on an outpatient basis for watery diarrhea (18), respiratory tract infections (4), or urinary tract infection (1). Detailed clinical assessment, videosigmoidoscopy, and histopathologic examination of endoscopic biopsies were performed for all.

RESULTS

Clinically, on presentation, bloody diarrhea was acute in all except 1 patient with a prolonged course (for 25 days) and stopped in all 2 to 6 days after discontinuation of antibiotics. Fever and/or leukocytosis were present only in 8 (34.8%). Sigmoidoscopy revealed varying types of erythema (patchy, ring, diffuse) and ulcers (aphthoid, diffuse) in 18 and pseudomembranes in 5. Histopathologically, only 3 showed the characteristic mushroom-like pseudomembranes, whereas all of the other infants had nonspecific colitis.

CONCLUSIONS

Community-acquired AABD is not uncommon in infants presenting with acute or chronic forms even without fever or leukocytosis. When suspected, discontinuation of antibiotics is a good policy if facilities for bacterial culture with cytotoxin assays are limited. The characteristic endoscopic or histopathologic pseudomembranes are encountered only in a small percentage (26%). Rational use of antibiotics should be adhered to particularly in cases of watery diarrhea that is mostly of viral origin.

Identification of a pseudo-outbreak of Clostridium difficile infection (CDI) and the effect of repeated testing, sensitivity, and specificity on perceived prevalence of CDI

OBJECTIVE

To describe a pseudo-outbreak of Clostridium difficile infection (CDI) caused by a faulty toxin assay lot and to determine the effect of sensitivity, specificity, and repeated testing for C. difficile on perceived CDI burden, positive predictive value, and false-positive results.

DESIGN

Outbreak investigation and criterion standard.

PATIENTS

Patients hospitalized at a tertiary care hospital who had at least 1 toxin assay for detection of C. difficile performed during the period from July 1, 2004, through June 30, 2006.

METHODS

The run control chart method and the chi(2) test were used to compare CDI rates and the proportion of positive test results before, during, and after the pseudo-outbreak. The effect of repeated testing was evaluated by using 3 hypothetical models with a sample of 10,000 patients and various assay sensitivity and specificity estimates.

RESULTS

In November of 2005, the CDI rate at the hospital increased from 1.5 to 2.6 cases per 1,000 patient-days (P < .01), and the proportion of positive test results increased from 13.6% to 22.1% (P < .01). An investigation revealed a pseudo-outbreak caused by a faulty toxin assay lot. A decrease of only 1.2% in the specificity of the toxin assay would result in a 32% increase in perceived incidence of CDI at this institution. When calculated by use of the manufacturer's stated specificity and sensitivity and this institution's testing practices, the positive predictive value of the test decreased from 80.6% to 4.1% for patients who received 3 tests.

CONCLUSION

Specificity is as important as sensitivity when testing for CDI. False-positive CDI cases can drain hospital resources and adversely affect patients. Repeated testing for C. difficile should be performed with caution.

Identification and screening for antimicrobial activity against Clostridium difficile of Bifidobacterium and Lactobacillus species isolated from healthy infant faeces

The antimicrobial activity against Clostridium difficile of 109 lactic acid bacteria (LAB) isolated from 32 healthy Korean infants was measured. The ability to show similar activity against Escherichia coli O157:H7 and Staphylococcus aureus was also looked for. Twelve of the 109 LAB showed activity against C. difficile and 19 strains were active against E. coli O157:H7, but none against S. aureus. Four strains had antimicrobial activity against both C. difficile and E. coli O157:H7. Of the 12 strains that had activity against C. difficile, four strains were excluded as Streptococcus species, while the other eight were identified using polymerase chain reaction (PCR) assays using group-specific primers designed from the nucleotide sequences of the 16S rDNA and internal transcribed spacer (ITS) regions of the Bifidobacterium and Lactobacillus species. Based on the sequencing results, the eight strains screened were identified as Bifidobacterium infantis and Lactobacillus salivarius.

Evaluation of six commercial assays for the rapid detection of Clostridium difficile toxin and/or antigen in stool specimens

OBJECTIVE

To evaluate six commercially available assays for the detection of Clostridium difficile toxin and/or antigen in stool samples: one latex agglutination test (Culturette brand CDT, Becton Dickinson), two ELISAs (Culturette brand Toxin CD, Becton Dickinson, and Ridascreen C. difficile Toxin A/B, R-biopharm), two chromatographic assays (Clearview C. difficile A, Oxoid, and ColorPac Toxin A, Becton Dickinson) and one enzyme immunoassay for the simultaneous detection of C. difficile common antigen and toxin A (Triage C. difficile Panel, Biosite).

METHODS

Over a period of 3 months, 366 liquid or semi-liquid stool samples were tested using cell-culture cytotoxin assay as standard, ethanol shock stool culture and latex agglutination (Culturette brand CDT). Of these, 78 samples, positive with at least one of these three methods, and 98 randomly selected negative samples were further evaluated using the other five kits. PCR was also performed on positive cultures to confirm the presence of toxin A and B genes.

RESULTS

Triage C. difficile Panel had the best sensitivity (95%), followed by Clearview C. difficile and ColorPac Toxin A (both 89%), Culturette brand Toxin CD (73%), Ridascreen C. difficile Toxin A/B (57%) and Culturette brand CDT (23%). For Triage, the sensitivity of C. difficile antigen detection was 93%, and the sensitivity of toxin detection was lower (77%). Most false-positive results were obtained with the Triage C. difficile Panel (25 specimens) and Clearview C. difficile A (20 specimens). Culturette brand CDT had the best specificity (99%); followed by Ridascreen C. difficile Toxin A/B (97%), Culturette brand Toxin CD (95%), ColorPac Toxin A (89%), Clearview C. difficile A (83%) and Triage C. difficile Panel (75%). The positive predictive values ranged from 68% to 94%, and the negative predictive values from 83% to 98%.

CONCLUSIONS

The sensitivity is much higher for Triage and the two new chromatographic assays than for the conventional EIAs. These tests also have a high negative predictive value. For Triage, C. difficile antigen-positive, toxin A-negative results can be obtained; the clinical value of these must be established by additional studies. Overall, the new-generation assays are still less sensitive than the cytotoxin assay; however, they provided same-day results, could be used as a screening test and may be useful in laboratories without tissue-culture facilities. Our results do not allow the recommendation of one single assay for the diagnosis of C. difficile-associated diarrhea. It remains the case that laboratory results must be correlated and interpreted with the clinical presentation of the patient.