Reply to Walker et al

To the Editor—We thank Walker et al for their interest in our work [1]. Our study found no evidence of difference in clinical severity of Clostridium difficile infection (CDI) between patients infected with ribotype 027/078 strains compared with others, when adjusted for other covariates [2]. Adjustment for factors on the hypothesized causal pathway between exposure (ribotype) and outcome (severity), such as leukocyte count, has been addressed elsewhere [3]. Removing the leukocyte count as a covariate or including it in the definition of severe disease did not alter our findings [3].