Evaluation of a Stenotrophomonas maltophilia bacteremia cluster in hematopoietic stem cell transplantation recipients using whole genome sequencing

ubiquitously occurs in the hospital environment. This opportunistic pathogen can cause severe infections in immunocompromised hosts such as hematopoietic stem cell transplantation (HSCT) recipients. Between February and July 2016, a cluster of four patients on the HSCT unit suffered from bloodstream infections (BSI). For epidemiological investigation we retrospectively identified the colonization status of patients admitted to the ward during this time period and performed environmental monitoring of shower heads, shower outlets, washbasins and toilets in patient rooms. We tested antibiotic susceptibility of detected isolates. Environmental and blood culture samples were subjected to whole genome sequence (WGS)-based typing. Of four patients with BSI, three were found to be colonized previously. In addition, retrospective investigations revealed two patients being colonized in anal swab samples but not infected. Environmental monitoring revealed one shower outlet contaminated with . Antibiotic susceptibility testing of seven strains resulted in two trimethoprim/sulfamethoxazole resistant and five susceptible isolates, however, not excluding an outbreak scenario. WGS-based typing did not result in any close genotypic relationship among the patients' isolates. In contrast, one environmental isolate from a shower outlet was closely related to a single patient's isolate. WGS-based typing successfully refuted an outbreak of on a HSCT ward but uncoverd that sanitary installations can be an actual source of transmissions.