Occurrence of fungi in water used at a haemodialysis centre

AIMS

The aim of this study was to identify and determine the diversity, occurrence and distribution of fungi in water used at a haemodialysis centre.

METHODS AND RESULTS

Samples in the hydraulic circuit for the distribution of the water, dialysate samples and samples of sterilization solution from dialysers were collected over a 3-month period, and 500 ml of each sample was filtered through membranes. All together 116 isolates of fungi were recovered from 89% of all water samples collected inside the haemodialysis unit, with prevalence of moulds in tap water samples and of yeasts in dialysate samples. Fusarium spp. was the most abundant genus found, whereas Candida parapsilosis was the predominant yeast species.

CONCLUSIONS

This study demonstrated that various fungi were present in the water system. These data suggest the inclusion of the detection and quantification of fungi in the water of haemodialysis.

SIGNIFICANCE AND IMPACT OF THE STUDY

The recovery of fungi from aqueous haemodialysis environments implies a potential risk for haemodialysis patients and indicates the need for continuous maintenance and monitoring. Further studies on fungi in haemodialysis water systems are required to investigate the organism ability to persist, their role in biofilm formation and their clinical significance.

Characterization of the DialGuardTM Device for Endotoxin Removal in Hemodialysis

Bacterial pyrogens, capable of penetrating dialyzer membranes, are responsible for a systemic inflammatory reaction in hemodialysis patients. Dialyzer reuse, involving rinsing of the dialyzer with pyrogen-containing water, may exacerbate this situation. Studies of the mechanism of action of endotoxin suggest that it irreversibly damages the vascular endothelium. The novel endotoxin removal method described here, is based on affinity-binding of endotoxin by the adsorbent ClarEtox, a USP Class VI-certified resin that is the active component of the medical device DialGuard. Under standard hemodialysis operating conditions, challenge of DialGuard with Pseudomonas maltophilia supernatant-spiked dialysate, containing 35-193 EU/ml endotoxin, resulted in endotoxin levels below 0.05 EU/ml in the treated dialysate. DialGuard was able to decrease endotoxin concentrations in the dialysate from a range of 2.39-8.49 to <0.005 EU/ml. DialGuard supports high fluid velocities at low back pressures and can be sanitized using the heat sanitization cycle of hemodialysis machines. DialGuard offers a simple, user-friendly way to reduce the concentration of endotoxin in dialysate and water for dialysis at a low cost.

Microbial contamination of dialysate and its prevention in haemodialysis units

At the haemodialysis centres of nine hospitals in Japan, microbial contamination of treated water (reverse osmosis method), acid and bicarbonate concentrates, and dialysate was investigated. Among these fluids used in haemodialysis, the dialysate was most frequently contaminated and had the highest concentration of bacteria. Of 40 dialysate samples analysed, 42.5% showed a bacterial count of more than 2000cfu/mL, which was above the Association for the Advancement of Medical Instrumentation (AAMI) standard. However, among the 40 samples from 20 dialysis machines, all six dialysate samples from three dialysis machines that used an ultrafiltration membrane in the circuit before the entrance of the dialysate into the dialyser, showed a bacterial count of < or =10 cfu/mL. In addition, when an ultrafiltration membrane was used in the circuit before the entrance of the dialysate into the dialyser for four dialysis machines showing dialysate samples contaminated with 10(4)-10(5)cfu/mL the bacterial count in dialysate samples from these machines became zero. Because dialysis machines are susceptible to microbial contamination, it is necessary to take measures such as placing an ultrafiltration membrane into the circuit before the entrance of dialysate into the dialyser.

Inflammatory response of a new synthetic dialyzer membrane. A randomised cross-over comparison between polysulfone and helixone

Hemodialysis patients suffer from chronic inflammation due to intradialytic contact of blood with artificial materials. The FX 60 dialyzer which belongs to the new FX-class series of dialyzers is composed of the new membrane Helixone. This membrane is derived from the original Fresenius Polysulfone membrane. The FX-class design is based on modified geometry of fibres and housing and has resulted in a new dialyzer with improved efficiency, safety and ease of handling compared to the F series (F 60S) dialyzer. The aim of the study was to investigate whether the biocompatibility pattern in terms of inflammatory parameters of the new type of polysulfone dialyzer has changed compared to the standard. A clinical in vivo study was conducted to compare the intradialytic inflammatory response of the two dialyzers, FX 60 and F 60S. Eight chronic dialysis patients were selected for the study: mean age 65.5 +/- 15.5 years, mean time on dialysis 100 +/- 95 months. The randomized cross-over study involved a treatment period of 2 weeks (total 6 sessions), one week with each dialyzer, starting with one or the other according to the randomization scheme. Blood samples were taken at 0 (T0), 15, 60, and 240 minutes to evaluate white blood cell (WBC) count, complement factor C5a, leukocyte elastase, soluble intercellular adhesion molecule 1 (sICAM-1), platelet count, C-reactive protein (CRP). At 15 min, WBC count showed a comparably, low decrease for both dialyzers: -7.6% for FX 60 versus -6.6% for F 60S, p=not significant (ns). At the same time the C5a concentration decreased from 15.0 +/- 7.5 ng/ml to 13.5 +/- 6.7 ng/ml (p=ns) for FX 60, and from 15.1 +/- 12.5 ng/ml to 14.9 +/- 25.0 ng/ml for F 60S (p=ns). The elastase concentration progressively increased over time with no statistical difference between the two dialyzers. The levels of sICAM-1, CRP, and platelet count were similar at each time point for both dialyzers, varying around the baseline values (p=ns). No significant difference emerged in terms of inflammatory response between the two dialyzers, hemo demonstrating that the biocompatibility of the F-series was maintained in the FX-class series of dialyzers and is independent of design factors.

Verification of the chemical composition and specifications of haemodialysis membranes by NMR and GPC-FTIR-coupled spectroscopy

The chemical composition of a dialysis membrane is decisive towards determining its physical and biochemical properties--two fundamental determinants of the success of therapy offered to patients suffering from chronic renal failure. From the vast variety of synthetic polymers available, only a few are suitable for the manufacture of dialysis membranes that have to conform to the diverse demands of modern haemodialysis and related therapies. Recently, a membrane labelled as polyamide (Polyamide S) has caused some confusion to end-users in that the product specification for the membrane is given as 'polyarylethersulfone' or simply as Polyamide S membrane. As the chemical and physical properties of these two polymer types are distinctly different, it is unclear whether the functional characteristics of Polyamide S are to be attributed to polyamide, polyarylethersulfone, or, to both polymers. We therefore undertook investigations to ascertain the exact chemical nature of the Polyamide S membrane using a series of chemical analytical tools and an appropriate polyamide reference. The analytical techniques were conventional gel permeation chromatography (GPC), GPC-FTIR coupled spectroscopy using dimethyl acetamide and hexafluoroisopropanol as solvents and nuclear magnetic resonance spectroscopy. Glass transition temperature measurements and quantitative elemental analysis were also carried out. None of the analytical techniques used showed any traces of polyamide in Polyamide S; no aliphatic or aromatic polyamide chemical entities were detected in any of the samples tested. The Polyamide S dialysis membrane thus comprises, solely, of polyarylethersulfone, which is also known as polyethersulfone.

Filtration fluid for hemodialysis treatment

Bacterial contamination of dialysis fluid has long been recognized as a problem in hemodialyis. Cytokines released as a consequence of contaminated dialysis fluid are believed to be responsible for many acute and chronic side effects in patients undergoing renal replacement therapy. For several years now, attempts have been made to eliminate pyrogenic substances and ensure a sterile and endotoxin-free dialysis fluid. A recent dialysis fluid filter known as DIASAFE, containing a membrane based on Polysulfone (Fresenius), was tested for a period of 1,000 hours (approx. 14 weeks). Dialysis fluid samples were collected once weekly before and behind the filter and cultivated for detection of microorganisms and endotoxins. Additionally, starting after the fourth week of the study, serum samples were collected weekly and the beta2-microglobulin concentration was determined. The filter reduced microorganisms at a rate of at least 10(5) and in the majority of cases (86% of samples) by more than 106. Under clinical conditions the stability and microbiological functionality of the filters could be demonstrated for more than 1,000 hours and 150 disinfecting cycles. In four cases of endotoxin burden (> 0.5 IU/ml) in the dialysis fluid in front of the filter the concentration behind the filter was lower than 0.1 IU/ml, indicating effective reduction of endotoxins. A tendency to a reduction of beta2-microglobulin in serum from 32.5+/-3.9 mg/L to 21.5+/-5.3 mg/L was observed. These results indicate that the dialysis fluid filter used was effective, dramatically reducing the bacterial contaminants in dialysis fluid, thus protecting patients from the potentially harmful acute and long-term life-threatening consequences of contaminated dialysis fluid.

Dialysis membranes today

In recent years, hemodialytic therapies have evolved from the simple, diffusion-dependent removal of small molecular weight substances from blood to advanced therapy modalities involving the convective removal of larger uremic sloutes. The clinical benefits of removal of substances such as beta2-microglobulin (beta2-m) have been reported by several authors: elimination of large-molecular weight "uremic toxins" is now widely accepted as being beneficial to the overall quality of life of patients. This trend would not have been possible without parallel technical developments, especially that of new membranes having more open pore structures resulting in higher sieving coefficients and increased hydraulic permeability. Not all polymer types are suitable for the manufacture of high-flux membranes required for convective therapies in which large fluid volumes are exchanged. Amongst the more important criteria are: the selected polymer must be able to undergo steam sterilisation, have high endotoxin retention capabilities, be versatile for the fabrication of a range of hydraulic permeabilities and, of course, have high blood compatibility. The aim of this paper is, firstly, to review the major membrane development phases over the last quarter of a century. Secondly, the suitability of current membrane materials to meet the aforementioned requirements will be examined. Thirdly, in view of the recent, rapid proliferation of polysulfone-based membranes, dialysis membranes of the polysulfone 'family' are placed under scrutiny; membranes of this class represent a significant portion of the product portfolio of dialyser manufacturers today, yet, few end-users are able to distinguish between the salient features of the respective products because of a combination of confusing membrane nomenclature, classification, tradenames and product claims.

Defining the microbiological quality of dialysis fluid

With increasing awareness about the degree and the potential impact of microbiological contamination in dialysis fluids, there is a desire to improve their microbiological quality. To achieve this goal, the origin of the microbiological contamination has to be identified. The water, the bicarbonate concentrate, and the fluid distribution system can be major contributors. Regular disinfection of the entire fluid path is necessary to prevent the formation of biofilm. The bicarbonate concentrate should be handled with special attention because it constitutes an excellent growth medium for microflora that may not be detected with regular assays. With a well maintained reverse osmosis (RO) system, frequent disinfection of the entire flow path, and microbiological awareness, it is possible to produce dialysis fluid that meets the most stringent standard (<10(2) colony forming units (CFU)/ml and <0.25 IU/ml of endotoxin). Adding a step of ultrafiltration just before the dialyzer can make the dialysis fluid ultrapure (<10(-1) CFU/ ml and <0.03 IU/ml). One additional step of controlled ultrafiltration provides sterile and pyrogen-free fluids (<10(-6) CFU/ml and <0.03 IU/ml) that can be used for infusion.