Clinical significance of direct cytotoxicity and toxigenic culture in Clostridium difficile infection.
BACKGROUND
Clostridium difficile infection (CDI) is the leading cause of hospital-acquired diarrhoea in developed countries. Although an optimal diagnosis is crucial, laboratory diagnostics remain challenging. Currently, the reference methods are direct cytotoxicity assay and toxigenic culture; however there is controversy in the interpretation of discordant results of these tests.


OBJECTIVE
The aim of our study was to determine the clinical significance of detecting C. difficile only by toxigenic culture with a negative direct cytotoxicity assay.


METHODS
We conducted a prospective study in which patients aged >2 years with CDI were enrolled and monitored at least 2 months after their last episode. Samples were tested by both cytotoxicity assay and toxigenic culture.


RESULTS
During the 6-month study period, we identified 169 episodes meeting CDI criteria that had been tested by both assays, out of which 115 were positive for both cytotoxicity assay and toxigenic culture, and 54 CDI episodes (31.9%) were positive only by toxigenic culture. Overall, patients median age was 71.3, 50.9% were male and the most frequent underlying disease was malignancy. The comparison of CDI episodes positive for both assays and by toxigenic culture only revealed the following, respectively: mild CDI (77.4% vs 94.4%; p = 0.008), severe CDI (21.7% vs 5.6%; p = 0.008), severe complicated (0.9% vs 0.0%; p = 1.000), pseudomembranous colitis (1.7% vs 1.9% p = 1.000), recurrence (17.4% vs 14.8%; p = 0.825), overall mortality (8.7% vs 7.4%; p = 1.000) and CDI related mortality (2.6% vs 0%; p = 0.552).


CONCLUSIONS
CDI episodes positive by cytotoxicity assay were more severe than those positive only by toxigenic culture, however there were a significant proportion of CDI cases (31.9%) that would have been missed if only cytotoxicity had been considered as clinically significant for CDI treatment, including severe CDI cases. Our data suggest that a positive test by toxigenic culture with a negative result for cytotoxicity should not be interpreted as colonization.
Department of Clinical Microbiology and Infectious Diseases, Hospital General Universitario Gregorio Marañón, Madrid, Spain; Medicine Department, School of Medicine, Universidad Complutense de Madrid (UCM), Madrid, Spain; Instituto de Investigación Sanitaria Gregorio Marañón, Madrid, Spain. Electronic address: helenrei@hotmail.com.
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Reigadas
Department of Clinical Microbiology and Infectious Diseases, Hospital General Universitario Gregorio Marañón, Madrid, Spain; Instituto de Investigación Sanitaria Gregorio Marañón, Madrid, Spain; CIBER de Enfermedades Respiratorias (CIBERES CB06/06/0058), Madrid, Spain.
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Alcalá
Department of Clinical Microbiology and Infectious Diseases, Hospital General Universitario Gregorio Marañón, Madrid, Spain; Medicine Department, School of Medicine, Universidad Complutense de Madrid (UCM), Madrid, Spain; Instituto de Investigación Sanitaria Gregorio Marañón, Madrid, Spain; CIBER de Enfermedades Respiratorias (CIBERES CB06/06/0058), Madrid, Spain.
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Marín
Department of Clinical Microbiology and Infectious Diseases, Hospital General Universitario Gregorio Marañón, Madrid, Spain.
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Muñoz-Pacheco
Department of Clinical Microbiology and Infectious Diseases, Hospital General Universitario Gregorio Marañón, Madrid, Spain.
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Catalán
Department of Clinical Microbiology and Infectious Diseases, Hospital General Universitario Gregorio Marañón, Madrid, Spain; Instituto de Investigación Sanitaria Gregorio Marañón, Madrid, Spain.
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Martin
Department of Clinical Microbiology and Infectious Diseases, Hospital General Universitario Gregorio Marañón, Madrid, Spain; Medicine Department, School of Medicine, Universidad Complutense de Madrid (UCM), Madrid, Spain; Instituto de Investigación Sanitaria Gregorio Marañón, Madrid, Spain; CIBER de Enfermedades Respiratorias (CIBERES CB06/06/0058), Madrid, Spain. Electronic address: emilio.bouza@gmail.com.
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Bouza
D000368:Aged; D000369:Aged, 80 and over; D015373:Bacterial Typing Techniques / Q000379:methods*; D002460:Cell Line; D019411:Clinical Laboratory Techniques / Q000379:methods; D016360:Clostridioides difficile / Q000254:growth & development; D003015:Clostridium Infections / Q000175:diagnosis*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies
Clostridium difficile infection; Colonization; Cytoxicity; Laboratory diagnosis; Toxigenic culture