PLoS Medicine by Sarah Walker et al. in the UK that measured the proportion of C. diff cases in hospitalized patients that were acquired during their index hospital stay. The results are pretty surprising. Using MLST, only ~25% of cases could be linked to inpatient transmission, ranging from 37% in renal/transplant down to 6% in specialist surgery. Additionally, many of the C. difficile cases linked to in-hospital transmission manifest soon after the index case appeared clinically. In the accompanying editorial, Harbarth and Samore suggest that this means "the hospital environment was not, as has previously been claimed, a long-lasting reservoir for this pathogen."
1) Walker AS, et al PLoS Medicine February 2012
2) Harbarth S and Samore MH et al. PLoS Medicine (Editorial)