Microwave: practical cost-effective method for sterilizing urinary catheters in the home

The microbiological and physical properties of catheters for intermittent catheterization: a systematic review on the impact of reuse and cleaning

STUDY DESIGN

Systematic Review.

OBJECTIVES

To review systematically the clinical evidence of the effectiveness of various intermittent catheter cleaning methods that have been proposed as methods to prepare catheters for reuse.

METHODS

A keyword search in Medline, Excerpta Medica dataBASE, the Cumulative Index to Nursing and Allied Health Literature, Web of Science and Cochrane Central Register of Controlled Trials, was undertaken to identify all English, Russian and German language literature evaluating the effectiveness of various intermittent catheter cleaning methods. Studies selected for review included analytical experimental, prospective cohort and cross-sectional. Cleaning methods reviewed included heat-based sterilization, chemical cleaning solutions, mechanical abrasion, photocatalytic sterilization, and combined methods.

RESULTS

Overall, 12 studies were included. Heat-based sterilization and mechanical abrasion methods were either not effective or damaged the physical properties of catheters. Two studies reported evidence that their chemical cleaning methods (i.e., soaked catheters in a 70% alcohol solution for 5 min or combined approach detergent wash followed by soaking in Milton sterilizing fluid also known as the Milton method) both preserved the structural integrity of their catheters and were bactericidal.

CONCLUSIONS

Numerous cleaning methods resulted in the destruction of catheters. However, there are two reported cleaning methods, submersion for 5 min in 70% alcohol and the "Milton method", that eliminate bacterial colonization while leaving the physical properties of the catheters unchanged. While these cleaning methods are promising, each was published in just one study, therefore higher-powered / longitudinal studies confirming the safety and efficacy of these cleaning methods must be obtained before current clinical recommendations can be modified.

An effective evidence-based cleaning method for the safe reuse of intermittent urinary catheters: In vitro testing

AIMS

To determine a safe bactericidal cleaning method that does not damage urethral catheters used for intermittent catheterization. In some countries, single-use catheters are the norm; in others, the reuse of catheters is common depending on health insurance, personal preference, or individual concerns about the environment. However, no recent study of cleaning methods has been published to provide evidence for the safe reuse of catheters.

METHODS

Using advanced microbiological methods, a laboratory study of eight cleaning methods was conducted. Sections of uncoated polyvinylchloride (PVC) catheters were exposed to bacterial uropathogens in physiologically correct artificial urine media then tested with a range of heat, chemical, and mechanical cleaning methods. Analysis of culturable and viable but nonculturable (VBNC) bacteria was done and direct microscopy was used. Descriptive statistics were used to compare values.

RESULTS

Heat treatments, although effective, resulted in catheter surface breakdown and damage. Ultrasonic cleaning and vinegar showed evidence of VBNC populations indicating the methods were bacteriostatic. Detergent and water wash followed by immersion in a commercially available 0.6% sodium hypochlorite solution and 16.5% sodium chloride (diluted Milton) gave consistent bactericidal results and no visible catheter damage.

CONCLUSIONS

Combined mechanical and chemical treatment of a detergent and water wash followed by immersion in diluted Milton (the "Milton Method") provided consistent and effective cleaning of uncoated PVC catheters, showing bactericidal action for all uropathogens tested after repeated exposure. If found safe in clinical testing, this method could increase the reuse of catheters, reduce plastic waste in the environment, reduce cost, and increase patient choice.

Diagnosis, prevention, and treatment of catheter-associated urinary tract infection in adults: 2009 International Clinical Practice Guidelines from the Infectious Diseases Society of America

Guidelines for the diagnosis, prevention, and management of persons with catheter-associated urinary tract infection (CA-UTI), both symptomatic and asymptomatic, were prepared by an Expert Panel of the Infectious Diseases Society of America. The evidence-based guidelines encompass diagnostic criteria, strategies to reduce the risk of CA-UTIs, strategies that have not been found to reduce the incidence of urinary infections, and management strategies for patients with catheter-associated asymptomatic bacteriuria or symptomatic urinary tract infection. These guidelines are intended for use by physicians in all medical specialties who perform direct patient care, with an emphasis on the care of patients in hospitals and long-term care facilities.

Color Stability of Dry Earth Pigmented Maxillofacial Silicone A-2186 Subjected to Microwave Energy Exposure

PURPOSE

The purpose of this study was to measure spectrophotometrically the color stability of pigmented A-2186 silicone maxillofacial elastomer with 10% by volume of titanium white dry earth opacifier before and after exposure to microwave energy over a simulated 1.5-year period of microwave sterilization.

MATERIALS AND METHODS

A-2186 silicone elastomer opacified with titanium white dry earth pigment, pigmented with 5 cosmetic dry earth pigment colors [no pigment (control) group (Pc), red (Pr), yellow ochre (Py), burnt sienna (Po), and a mixture of Pr + Py + Po color group (P3)], was used in this study. Each of the 5 experimental groups consisted of 5 specimens. All specimens were placed in a 250 ml glass beaker filled with 150 ml of water (replenished for each microwave exposure). An exposure of 6 minutes was used 18 times (simulating 1.5 years of microwave sterilization with one 6 minute exposure monthly). Reflectance values were measured by spectrophotometer. Three- and two-way analyses of variance with repeated measures were performed for the color difference (DeltaE*) with the factors of group/color/months, and group/months, respectively. Means were compared by Tukey Honest Significant Difference (HSD) multiple range test calculated at the 0.05 level of significance using SPSS.

RESULTS

The trained human eye can detect color changes (DeltaE*) greater than 1.0. Most DeltaE* values of the red pigment group at all intervals and the mixed pigment group at 15- and 18- month intervals increased significantly greater than 1.0 (p < 0.001) compared with the control group. Yellow and burnt sienna groups remained the most color stable over time with DeltaE* values below 0.35.

CONCLUSIONS

Lack of color stability of red dry earth pigmented A-2186 silicone maxillofacial elastomers was clinically significant after 12-month exposure to microwave energy as compared with yellow, burnt sienna, and opacified A-2186 dry earth pigments.

The Physical and Antimicrobial Effects of Microwave Heating and Alcohol Immersion on Catheters that Are Reused for Clean Intermittent Catheterisation

INTRODUCTION

Due to worldwide different health insurance policies, patients are often forced to reuse the catheters when performing Clean Intermittent Catheterisation (CIC). We have compared the physical qualities and the antimicrobial effects of two methods of reusing catheters: microwave heating and storage of the catheters in a 70% alcohol solution. The studies were performed during different lengths of time.

MATERIALS AND METHODS

Three types of catheters (a standard polyvinylchloride catheter, a special polyvinylchloride catheter with flexible Ergothan tip and a prelubrified catheter), normally intended for single use, were submitted to the effect of a microwave oven (Multitech 215 High Grade and Whirlpool M220 750 W and 1000 W with rotating plate) or preservation in a 70% alcohol solution. To study the effects of microwave heating, a recipient of water was placed in the oven to spread the microwaves and to absorb the heat. The catheters were placed in a resealable plastic bag (Ziploc. To study the effects of preservation in a 70% alcohol solution, the catheters were immerged in the solution for different lengths of time. Thereafter were the physical qualities of the catheters evaluated by using the technique of Differential Scanning Calorimetry (DSC). The antimicrobial effect of the method was evaluated after grafting the catheters with pathogenic E. coli, P. aeruginosa or S. aureus strains.

RESULTS

Microwave heating up to 12 minutes at 750 W caused only minimal changes in the physical qualities of all the catheters. However, there was only an antimicrobial effect of the microwave heating on E. coli and not on P. aeruginosa or S. aureus. If the catheter remained longer than 45 minutes in a 70% alcohol solution, the physical qualities of the catheter changed either minimal in the special polyvinylchloride catheter with flexible Ergothan top but changed significantly in the prelubrified catheter). However, already after 5 minutes of immersion in the 70% alcohol solution there was a complete antimicrobial effect on E. coli, P. aeruginosa and S. aureus in all catheters.

CONCLUSIONS

It should be recommended to patients on CIC to use a sterile packed and not previously used catheter. In this study we have shown that immersing the catheters in a 70% alcohol solution during 5 minutes can effectively disinfect the catheter without jeopardising the physical qualities. Thereafter, the catheters could be placed in a resealable (e.g. Ziploc bag without being rinsed under water, in order that the few drops of alcohol cause alcohol vapours within the closed plastic bag and maintain the antimicrobial effect.

Immobilized bacterial spores for use as bioindicators in the validation of thermal sterilization processes

Spores of Bacillus subtilis ATCC 6051 and Bacillus stearothermophilus NCTC 10003 were immobilized in monodisperse alginate beads (diameter, 550 microm +/- 5%), and the capacity of the immobilized bioindicators to provide accurate and reliable F-values for sterilization processes was studied. The resistance of the beads to abrasion and heat was strong enough to ensure total retention of the bioindicators in the beads in a sterilization cycle. D- and z-values for free spores were identical to those for immobilized spores, which shows that immobilization does not modify the thermal resistance of the bioindicators. A D(100 degrees C) value of 1.5 min was found for free and immobilized B. subtilis spores heated in demineralized water, skimmed milk, and milk containing 4% fat, suggesting that a lipid concentration as low as 4% does not alter the thermal resistance of B. subtilis spores. Providing that the pH range is kept between 3.4 to 10 and that sufficiently low concentrations of Ca2+ competitors or complexants are present in the medium, immobilized bioindicators may serve as an efficient, accurate, and reliable tool with which to validate the efficiency of any sterilization process. The environmental factors (pH, media composition) affecting the thermoresistance of native contaminants are intrinsically reflected in the F-value, allowing for a sharper adjustment of the sterilization process. Immobilized spores of B. stearothermophilus were successfully used to validate a resonance and interference microwave system that is believed to offer a convenient alternative for the sterilization of temperature-sensitive products and medical wastes.

Transurethral microwave thermotherapy for the treatment of prostatitis

The lethal action of microwaves on various microorganisms is well established and has been exploited in various clinical settings. Transurethral microwave thermotherapy (TUMT) has become a recognized modality for the treatment of prostatic diseases. Recently, it has been applied for the treatment of patients with nonbacterial prostatitis unresponsive to traditional therapeutic schemes. We review the current literature and present our recent encouraging experience with the in vitro bactericidal effect of microwaves on bacteria considered possible etiologic agents of prostatitis. Thus, we may consider the application of TUMT in patients with chronic bacterial prostatitis.

Killing activity of microwaves in milk

The killing activity of microwaves of 2450 MHz frequency and 600 W power on Pseudomonas aeruginosa, Escherichia coli, Enterobacter sakazakii, Klebsiella pneumoniae, Staphylococcus aureus, Candida albicans, Mycobacterium terrae and poliomyelitis vaccine-virus suspended in five infant formula preparations was investigated. The samples were brought to the boil (85-100 s depending on milk type). They had reached average temperatures of 82-93 degrees C at this point. Most of the vegetative organisms were killed. In those samples where growth was still detectable after microwave treatment, a significant reduction in viable micro-organisms (at least 5000-fold) was noted. We conclude that microwave beating to the boil is a convenient and fast method to reduce microbial contamination of infant feeds. However, care should be taken to ensure that milk is adequately cooled to the required temperature before it is fed to an infant.

Comparison study of home catheter cleaning methods

Three methods of cleaning urinary catheters for reuse at home by clients on intermittent catheterization programs were studied. Reused catheters were collected from clients, autoclaved, and then incubated in a culture of Escherichia coli broth. Three different isolates of E. coli were used at concentrations ranging from 4.8 x 10(5) to 1.0 x 10(8) colony-forming units per milliliter. The catheters were then rinsed with tap water for 1 minute and soaked in one of three cleaning solutions for 30 minutes. The three cleaning solutions studied were 0.6% hydrogen peroxide, bleach in a 1:4 solution with tap water, and betadine in a 1:2 solution with tap water. None of the cleaned catheters showed detectable growth for 48 hours after the cleaning procedure was performed.

The bactericidal effect of microwaves on Mycobacterium bovis dried on scalpel blades

The action of microwaves on stainless steel scalpel blades contaminated with Mycobacterium bovis was investigated. The complete destruction of M. bovis was obtained with 4 min of microwave exposure. When the preparations were subjected to scanning electron microscopy, the bacteria had undergone a progressive series of alterations consisting, initially, of the formation of deep pits in the bacterial body and eventually the complete disintegration of the microorganisms. Such phenomena are less evident when this mycobacterium is exposed to other sterilization methods such as dry heat or autoclaving.

Bacteriuria in intermittent catheterization users: the effect of sterile versus clean reused catheters

Monthly urine cultures were analyzed at the University of Alberta Department of Medical Microbiology and Infectious Diseases to determine whether single-use sterile catheters and clean technique reduced the incidence of bacterial colonization in those using long-term intermittent self-catheterization. Thirty subjects with spina bifida, ages 3 years to 16 years, entered a crossover study with random assignment to 6 months of sterile single-use catheters or clean reused catheters. Seventeen subjects were catheterized by a parent or caregiver; 13 were responsible for self-catheterization and cleaning of the catheters. Six months of descriptive data were also collected at Alberta Children's Hospital from a similar group of subjects with spina bifida who used sterile catheters only. In the crossover group, 38% of all urine cultures were positive regardless of whether sterile single-use or clean reused catheters were employed. The other group using only sterile catheters had a 36% positive culture rate. No difference in positive cultures was found between males and females or between children who catheterized themselves and children whose parents catheterized them. The authors concluded that plastic urethral catheters may be reused.

Microwave sterilization of polyethylene catheters for intermittent self-catheterization

A standard household 650 W microwave oven was used to sterilize polyethylene catheters of the type used for intermittent self-catheterization. The catheters were infected with Proteus sp. bacteria and microwaved at 650 W for periods of 2, 4, 6 and 8 minutes. The effect of microwaving was assessed by determining the resultant colony counts following catheter culture. It was determined that 6 minutes of microwaving were required to achieve sterility. It is suggested that use of a microwave oven is a reliable and cost-effective method of sterilizing polyethylene catheters for intermittent self-catheterization.

The killing activity of microwaves on some non-sporogenic and sporogenic medically important bacterial strains

The killing activity of microwaves of 2450 MHz frequency and 325 W, 650 W and 1400 W power on some bacterial strains was investigated. Vegetative strains of Staphylococcus aureus, Streptococcus pyogenes Group A, Escherichia coli, Pseudomonas aeruginosa and Enterococcus faecalis and spores of Bacillus subtilis and Bacillis stearothermophilus in aqueous suspensions were exposed to 325 W and 650 W waves for different lengths of time. Enterococcus faecalis and spores of B. subtilis and B. stearothermophilus were exposed additionally to 1400 W waves in aqueous and 'dried' suspensions. Vegetative bacteria were promptly killed in 5 min or less, E. faecalis being slightly more resistant. Bacterial spores were only killed in aqueous suspension when a 1400 W setting was used for 10 to 20 min. Bacterial spores adhering to the tube walls after the aqueous suspension was poured out were reduced in number. We assume that the conventional microwave ovens available on the market may be used for a high level of disinfection but not for sterilization, and only then if sufficient water is present.