Lack of association of tcdC type and binary toxin status with disease severity and outcome in toxigenic Clostridium difficile.

The production of binary toxin and presence of truncating mutations in the putative toxin repressor gene, tcdC, have been associated with the increased virulence and spread of Clostridium difficile, especially ribotype 027. We analysed the prevalence of binary toxin genes and tcdC mutations in 207 clinical C. difficile isolates collected between 2008-2010. The majority (83%) belonged to one of five tcdC types and 8% were ribotype 027. There was little evidence of epidemic spread but there was a high prevalence of both predicted tcdC truncating mutations (15%) and binary toxin genes (28%), which occurred in both 027 and other ribotypes. We measured risk factors (age and laboratory markers) and patient outcomes (severity of disease, ICU admission, mortality, recurrence and length of stay) for patients infected with C. difficile strains with and without these mutations and genes. There was a significantly higher serum C-reactive protein and total peripheral white cell count in the group with predicted tcdC truncating mutations, but no difference in patient outcome. The group with binary toxin genes had a significantly higher total peripheral white cell count and 30 day all cause mortality. We have demonstrated a high prevalence of both predicted tcdC truncating mutations and binary toxin genes in a variety of C. difficile ribotypes, however neither of these factors by themselves predicted clinical virulence. This and other work show that commonly described deletions and truncating mutations do not by themselves explain the virulence of ribotype 027 and other C. difficile strains and further work is required to explain why some isolates appear to produce more severe disease than others.