Novosad SA, Lake J, Nguyen D, et al. - Via matched case-control studies, researchers examined an outbreak of Gram-negative bloodstream infections at 3 outpatient hemodialysis facilities, including 58 cases, of which hospitalization was needed in 48 (83%). The odds of using a central venous catheter for dialysis were higher in cases vs controls. S marcescens and P aeruginosa were identified in the environmental samples from wall boxes. As per results of pulsed-field gel electrophoresis and whole-genome sequencing, a close link was found between S marcescens isolated from wall boxes and case-patients from the same facilities. Findings revealed an association of this large outbreak with wall boxes, a previously undescribed source of contaminated fluid and biofilms in the immediate patient care environment.