- Background: Pseudomonas aeruginosa, especially multidrug-resistant (MDR) isolates, is an important pathogen in allogeneic hematopoietic stem cell transplant (HCT) recipients. The ability to identify patients at risk for these infections and administer appropriate empiric therapy, particularly during episodes of neutropenia, may improve outcomes and also direct infection control and antimicrobial stewardship efforts. Many transplant centers obtain routine surveillance stool cultures (SSCs) from HCT recipients to test for colonization with vancomycin-resistant enterococci, and extended-spectrum beta lactamase-producing Enterobacteriaceae. Our center initiated the performance of SSCs for P. aeruginosa, because of a perceived increase in the frequency of infection with MDR strains. The aim of this study was to determine the utility of this practice. Methods: We conducted a 2-year (2010-2011) retrospective review of the medical records of all patients who underwent allogeneic HCT at our cancer center to (a) determine the frequency of fecal colonization with P. aeruginosa, including MDR strains; (b) to determine the overall frequency of subsequent P. aeruginosa infection, as well as the frequency of infection with MDR strains; (c) to ascertain the proportion of subsequent infections likely arising from the intestinal tract; and (d) to determine risk factors for progression from colonization to infection. Results: Of 794 study patients, 58 (7.3%) had at least 1 positive SSC for P. aeruginosa; 19/58 (32.8%) developed a subsequent pseudomonal infection (11 with matching antimicrobial resistance patterns). On the other hand, 37/736 (5%) of the patients who were not colonized, developed a pseudomonal infection. The type of infection observed was pneumonia in 26 (46%) patients, bloodstream infection in 20 (36%), urinary tract infection in 8 (14%), and infections at other sites in 2 (4%). The incidence of MDR P. aeruginosa in the entire cohort was 2.2% (18 of 794): 12 had positive SSCs and 7 of these patients later developed MDR P. aeruginosa infections. Patients with acute myelogenous leukemia were more likely to be colonized and to develop subsequent infection. No infection-related deaths were observed during the first 30 days after infection. Conclusions: The incidence of P. aeruginosa colonization and subsequent infection was low. Patients who were not colonized had a low chance of developing P. aeruginosa infection. Most patients who developed infection did not have fecal colonization, suggesting a different source of infection. SSCs for P. aeruginosa provide incomplete information regarding the source of infection.