A cluster of bloodstream infections and pyrogenic reactions among hemodialysis patients traced to dialysis machine waste-handling option units

From June 17 through November 15, 1995, ten episodes of Enterobacter cloacae bloodstream infection and three pyrogenic reactions occurred in patients at a hospital-based hemodialysis center. In a case-control study limited to events occurring during October 1-31, 1995, seven dialysis sessions resulting in E. cloacae bacteremia or pyrogenic reaction without bacteremia were compared with 241 randomly selected control sessions. Dialysis machines were examined, dialysis fluid and equipment were cultured, and E. cloacae isolates were genotyped by pulsed-field gel electrophoresis. Each dialysis machine had a waste-handling option (WHO) through which dialyzer-priming fluid was discarded before each dialysis session; in 7 of 11 machines, one-way check valves designed to prevent backflow from the WHO into patient bloodlines were dysfunctional. In the case-control study, case sessions were more frequent when machines with greater than or equal to 1 dysfunctional check valves were used. E. cloacae with identical pulsed-field gel electrophoresis patterns were isolated from case patients, dialysis fluid, station drains, and WHO units. Our investigation shows that bloodstream infections and pyrogenic reactions were caused by backflow from contaminated dialysis machine WHO units into patient bloodlines. The outbreak was terminated when WHO use was discontinued, check valves were replaced, and dialysis machine disinfection was enhanced.