Microbiological monitoring of dialysis water systems ‑ is there a need for increased sampling?

R James

The Royal London Hospital

PROBLEM Assurance of adequate water quality is one of the most important aspects of ensuring a safe and effective delivery of haemodialysis. An extensive microbiological survey of several water systems highlighted a contamination problem which routine sampling had failed to detect.

PURPOSE The aim was to investigate whether or not our current microbiological testing regime

provided an effective method of monitoring the efficacy of the disinfection programme.

DESIGN Current guidelines suggest that samples for microbiological and endotoxin analysis should be taken from the outlet of water treatment plant and points expected to have the highest bacterial load, normally the end of the distribution loop and connections to the dialysis machines, where the flow is lowest. Points of connection to machines should be tested in `several month' rotation. The survey extended sampling to include all machine connection points.

FINDINGS Four systems were investigated. The bacterial culture method used was R2A media for 7 days at 22°C and endotoxin levels monitored using the Limulus Amoebocyte Lysate (LAL) assay. The samples from routine test points generally returned results within our operational limits (<10 CFU/ml and <0.06 EU/ml). However, results from several machine connection points on two sites exceeded these limits by a large margin. Several disinfection cycles were required in order to achieve results in keeping with our operational limits.

CONCLUSION Sample results from the end of the distribution loop may give a false sense of security by not indicating a contamination problem at the machine connection points. Increasing the number and frequency of machine connection points tested should provide greater security in detecting contamination and allowing for remedial action at an earlier stage.