An Unusual Cluster of Urinary Tract Infections, Including Salmonella spp., in an Iranian Ulcerative Colitis Cohort Treated With Vedolizumab: A Case Series and Comparative Analysis.

Background: Vedolizumab, a gut-selective α4β7 integrin antagonist, is widely used for the treatment of ulcerative colitis (UC) and is generally considered to have a favorable systemic infection safety profile. During routine clinical practice, we observed an unexpected clustering of urinary tract infections (UTIs) among patients initiating vedolizumab in an Iranian cohort, prompting further evaluation. Methods: This single-center, observational case series included 15 adult patients with moderate-to-severe UC treated with vedolizumab and followed prospectively for 12 weeks for the occurrence of UTIs. A contemporaneous comparator cohort of 30 UC patients treated with infliximab ( Results: Patients treated with vedolizumab demonstrated significant clinical improvement, with a mean Mayo score reduction from 8.2 to 3.5 during follow-up. An unexpectedly high number of early symptomatic UTIs was observed in the vedolizumab group, including cases caused by non-typhoidal Salmonella species, whereas no UTIs were detected in the small comparator cohorts. Given the limited sample size and observational design, reliable estimation of relative risk was not possible. Conclusions: In this small, single-center cohort, an unusual clustering of early symptomatic UTIs was observed among patients initiating vedolizumab. These findings are observational and hypothesis-generating, and no causal relationship can be inferred. They highlight the importance of real-world pharmacovigilance and the need for larger, multicenter studies to clarify whether such infection patterns reflect contextual clustering or reproducible safety signals influenced by regional epidemiological factors.