Multiple Clostridium Difficile Strains Cause Severe Patient Outcomes

Clostridium difficile is the most common cause of hospital acquired infections in the USA and the incidence of C. difficile infection (CDI) has increased dramatically since 2001, coinciding with the emergence of the epidemic ribotype 027 (R027).

The high mortality rate associated with R027 led to it being described as a hypervirulent strain and since that characterization, additional ribotypes of C. difficile have been described as hypervirulent using similar criteria, but the impact of C. difficile ribotype on disease outcomes remains unclear, especially in endemic rather than epidemic settings.


Scientists at the University of Houston College of Pharmacy (Houston, TX, USA) and their colleagues collected and cultured stool samples that tested positive for C. difficile toxin from patients who presented to any of seven different local hospitals from 2011 to 2013. The study included 715 patients aged 61 ± 18 years with females making up 63% of the study population.

Enzyme-linked immunoassay or a polymerase-chain reaction (PCR) detection of the tcdB gene in unformed stool was the diagnostic methodology used at all study sites during the study period. C. difficile toxin-positive stool samples were plated onto cefoxitin-cycloserine-fructose agar (CCFA) plates and incubated under strict anaerobic conditions for 48 to 72 hours. The growth of toxigenic C. difficile was confirmed using multiplex PCR to determine the presence of tcdA, tcdB, and binary toxin genes and fluorescent ribotyping was performed.

In this large multicenter study, C. difficile R027 was the most common ribotype and was associated with severe CDI presentation and severe CDI outcomes. Although R027 was independently associated with severe disease, R027 was not independently associated with severe outcomes. No single strain was more virulent than the others. The ribotype 014-020 was associated with significantly lower incidence of severe CDI and severe CDI outcomes compared with other ribotypes.

Samuel L. Aitken, PharmD, the lead author of the study, said, “Clinical severity markers of CDI, such as white blood cell count and albumin level, a protein in blood, are more important predictors of severe outcomes than any specific strain, especially in hospitals with no single predominant strain. Strain typing remains a valuable source of information for tracking emergence of different strains and may potentially influence treatment decisions, but clinical severity markers appear to be more important predictors for the determining the severity of CDI patient outcomes.” The study was published on August 20, 2015, in the journal Infection Control & Hospital Epidemiology.

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University of Houston College of Pharmacy