Does ultrapure dialysate prevent the development of biofilm in dialysis therapy?

Sir, Bio®lm, macroscopically visible as greenuyellowish deposit of ¯uid pipes, is commonly present in dialysis modules and parts of the water treatment system. Bio®lm consists of a ®ne ®brillar meshwork of bacterial origin, with trapped microorganisms w1x. The presence of bio®lm in dialysis systems is a point of concern, ®rst because bio®lms continuously release bacterial components such as peptidogly-cans and endotoxins. Moreover, bacteria present in bio®lm are highly resistant against cleaning and disinfection procedures and therefore eradication, once a bio®lm is present, is virtually impossible w1x. The continuous release of bacterial components into the dialysate may contribute to the activation of the immune system and, therefore, to a chronic in¯ammatory state in haemodialysis patients w2x. This suggests that prevention of the development of bio®lm is relevant in haemodialysis therapy. As contamination of the dialysate may lead to the development of bio®lm, the use of ultrapure dialysate is expected to result in a reduced development of bio®lm; however, no data on this subject are as yet available. In our hospital, a new water treatment system was installed in 1998, including continuous ultraviolet disinfection. Moreover, this installation is (except for the RO unit) treated