Atici, SerkanMemisoglu, Asli CinarAksu, BurakBilgen, Hulya SelvaOzek, ErenSoysal, Ahmet2026-03-152026-03-1520261471-233410.1186/s12879-026-12577-32-s2.0-105029686852https://doi.org/10.1186/s12879-026-12577-3https://hdl.handle.net/20.500.14517/8893Background Healthcare-associated infection outbreaks are frequently linked to environmental reservoirs, particularly contaminated water sources. Preterm infants in neonatal intensive care units (NICUs) represent a high-risk population for such outbreaks. Methods Through weekly rectal swab surveillance cultures in the NICU, we detected and contained a Stenotrophomonas maltophilia outbreak. Environmental sampling was performed to identify potential sources. Results S. maltophilia was isolated from 6 of 15 neonates during routine surveillance, representing an outbreak of colonization without invasive infection. Environmental cultures revealed contamination in the carboy water system (carboy water, carboy pump, and carboy tubes). Repetitive extragenic palindromic sequence analysis demonstrated clonal relatedness between environmental and clinical isolates, though not complete genetic identity (100%). Conclusion This outbreak highlights carboy water systems as a previously unreported source of S. maltophilia colonization in NICUs. The observed high genetic diversity among isolates was potentially driven by antibiotic selection pressure and differential distribution of gene expression. Our findings emphasize the critical role of routine surveillance cultures for early outbreak detection. During outbreaks, comprehensive environmental sampling, molecular surveillance beyond serotyping, and robust infection control measures are essential for successfully outbreak management.eninfo:eu-repo/semantics/openAccessNosocomial OutbreakGenetic DiversityStenotrophomonas MaltophiliaArticle