AbstractEvidence on risk factors for Clostridium difficile infection (CDI) in hemato-oncologic patients is conflicting. We studied risk factors for CDI in a large, well-characterized cohort of hemato-oncological patients. 144 hemato-oncological patients were identified in this retrospective, single center study with a microbiologically confirmed CDI-associated diarrhea. Patients were compared with 144 age and sex matched hemato-oncologic patients with CDI negative diarrhea. Risk factors such as prior antimicrobial therapy, type of disease, chemotherapy and survival were evaluated. CDI-positive patients received more frequently any antimicrobial agent and antimicrobial combination therapy than CDI-negative patients (79% vs. 67%; OR = 2.26, p = 0.038 and OR = 2.62, p = 0.003, respectively). CDI positive patients were treated more frequently with antimicrobial agents active against C. difficile than CDI negative ones (25% vs. 13%; OR = 2.2, p = 0.039). The interval between last chemotherapy and onset of diarrhea was significantly shorter in patients without CDI (median, 17 days vs 36 days; p < 0.001). Our study demonstrates that chemotherapy is not a significant risk factor for CDI but for early onset CDI negative diarrhea. The predominant modifiable risk factor for CDI is in hemato-oncological patients antimicrobial treatment. These findings should be taken into account in the daily clinical practice to avoid CDI associated complications and excess health care costs.