Background: CDI is the primary cause of infectious diarrhea in immunocompromised patients including those undergoing autologous stem cell transplant (SCT). Given the key role of gut microbiome and its interaction with host immune system, we investigated whether polymorphisms in innate immunity genes (identified through Ingenuity Pathway Analysis) were associated with CDI. Methods: We queried our database to identify MM patients who underwent an autologous SCT between April 2015-June 2019. Patients who had their buccal swabs collected through an IRB approved specimen collection protocol were included herein. Data were collected on age, conditioning regimen, CDI diagnosis, time from admission until CDI diagnosis, absolute neutrophil count (ANC) at time of CDI diagnosis, and antibiotic prophylaxis. Genomic DNA was extracted from buccal swabs and genotyped for 62 single nucleotide polymorphisms (SNPs) in ASPH, RLBP1L1, ATP7B, IL-8, FAK, TNFRSF14, CTH, TLR andIL-4. Univariate and multivariate logistic regression analyses were performed to assess association between CDI and presence of SNPs in these genes. Results: A total of 83 patients were identified (25 cases and 58 controls). Baseline characteristics were comparable between two groups. Median age was 67 years (range: 50-79). All patients received high dose melphalan as conditioning, and the same antibiotic prophylaxis during peri-transplant period. Median time from hospitalization until CDI diagnosis was 10 days (IQR:9 days), and median ANC was 0.7/mL (IQR:1.6/mL). Two SNPs (rs2227307 T > G in IL-8 and rs2234167 G > A in TNFRSF14) were significantly associated with CDI risk in both univariate and multivariate logistic regression analyses (Table). Conclusions: Our findings suggest that rs227307G (in IL-8) and rs2234167A (in TNFRSF14) alleles are potential risk factors for CDI after autologous SCT. Our findings, if validated in a larger cohort, would support genetic testing as a screening tool to identify patients who might benefit from prophylaxis against CDI.