An outbreak of gram-negative bacteremia in hemodialysis patients traced tohemodialysis machine waste drain ports

OBJECTIVE: To investigate an outbreak of gram-negative bacteremias at a hem odialysis center (December 1, 1996-January 31, 1997). DESIGN: Retrospective cohort study. Reviewed infection control practices an d maintenance and disinfection procedures for the water system and dialysis machines. Performed cultures of the water and dialysis machines, including the waste-handling option (WHO), a drain port designed to dispose of salin e used to flush the dialyzer before patient use. Compared isolates by pulse d-field gel electrophoresis. SETTING: A hemodialysis center in Maryland, RESULTS: 94 patients received dialysis on 27 machines; 10 (11%) of the pati ents had gram-negative bacteremias. Pathogens causing these infections were Enterobacter cloacae (n=6), Pseudomonas aeruginosa (n=4), and Escherichia coli (n=2); two patients had polymicrobial bacteremia. Factors associated w ith development of gram-negative bacteremias were receiving dialysis via a central venous catheter (CVC) rather than via an arterio-venous shunt (all 10 infected patients had CVCs compared to 31 of 84 uninfected patients, rel ative risk [RR] undefined; P<.001) or dialysis on any of three particular d ialysis machines (7 of 10 infected patients were exposed to the three machi nes compared to 20 of 84 uninfected patients, RR=5.8; P=.005). E cloacae, P aeruginosa, or both organisms were grown from cultures obtained from sever al dialysis machines. WHO valves, which prevent backflow from the drain to dialysis bloodlines, were faulty in 8 (31%) of 26 machines, including 2 of 3 machines epidemiologically linked to case-patients. Pulsed-field gel elec trophoresis patterns of available dialysis machine and patient E cloacae is olates were identical. CONCLUSIONS: Our study suggests that WHO ports with incompetent valves and resultant backflow were a source of cross-contamination of dialysis bloodli nes and patients' CVCs. Replacement of faulty WHO valves and enhanced disin fection of dialysis machines terminated the outbreak.