154
Letters
to the Editor
References 1. George
JD,
Yates
MD.
Infections
caused
by
opportunistic
mycobacteria:
a review.
r
R
Sot Med 1986: 79: 226-229. 2. Prince DS, Peterson DD, Steiner RM, et al. Infection with Mycobacterium avium complex in patients without predisposing conditions. N EnglJ Med 1989; 321: 863-868. 3. Nunn PP, McAdam KPWJ. Mycobacterial infections and AIDS. Br Med Bull 1988; 44: 801-813. 4. Wallace RJ. Nontuberculous mycobacteria and water: a love affair with increasing clinical importance. Infect Dis Clin North Am 1987; 1: 677-686. 5. Pelletier PA, du Moulin GC, Stottmeier KD. Mycobacteria in public water supplies: comparative resistance to chlorine. Microbial Sci 1988; 5: 147-148. 6. du Moulin GC, Stottmeier KD, Pelletier PA, Tsang, Anna Y, Hedley-Whyte J. Concentration of Mycobacterium avium by hospital hot water systems. JAMA 1988; 260: 1599-1601. 7. Iseman M. Atypical Mycobacterial Diseases. In: Mitchell RS, Petty TL, Schwarz MI, Eds. Synopsis of Clinical Pulmonary Disease, 4th edn. St. Louis: CV. Mosby Company 1989; 85-91. 8. British Society of Gastroenterology. Cleaning and disinfection of equipment for gastrointestinal flexible endoscopy: interim recommendations of a Working Party of the British Society of Gastroenterology. Gut 1988; 29: 113~115 1.
Sir, ‘Silverline’,
a device
for the prevention
of nosocomial
bacteriuria?
Hospital-acquired infections in England have been estimated to ‘have cost the National Health Service more than El14 million in 1987.’ Catheter-associated urinary tract infection is the most common of these, accounting for more than 30% of all reported nosocomial infections.2-4 Nearly 75% of patients with nosocomial urinary tract infection have undergone some form of urological instrumentation, often urinary catheterization, before their infection.5 The prevalence of urinary tract infection increases with the duration of catheterization, which is the predisposing factor most frequently associated with Gram-negative septicaemia and its mortality rate of 20-50°h.6 We have evaluated a device, ‘Silverline’ (Giltech Ltd, Ayrshire, Scotland, UK), consisting of a moulded tube containing a silver-releasing inorganic polymer. When in position, the insert is bathed in urine as it flows to the collection bag and it releases silver ions at a constant rate, for a period of seven days. Biocompatibility studies of the polymer have been undertaken.7 The well-documented broad-spectrum activity of silver7 is claimed to prevent bacteria entering the catheter lumen, to provide an antibacterial internal surface coating on the tubing and to act as a barrier against bacterial contamination following the use of the drainage tap and the sampling port. Patients of either sex who were admitted to the acute medical, surgical or urological wards of three participating hospitals, and who required short-term catheterization (up to 7 days), were included in our evaluation. Ethics committee approval and written informed consent was obtained from
Letters to the Editor
155
all patients. Silver cartridges, or placebo cartridges of identical appearance, were inserted aseptically between the catheter and the drainage bag at the time of catheterization. Patients who had been catheterized before admission to hospital were excluded. For the purpose of this study a catheter-associated bacteriuria was defined as the presence of 10’ cfu ml-’ of bacteria in the urine. Patients who had no bacteria at the first assessment and who subsequently developed growth of 10’ cfu ml-’ urine by day 5 of catheterization were, for the purposes of the study, identified as having a nosocomial bacteriuria. Mid-stream samples of urine were collected before catheterization and on day 5. When a patient remained catheterized for longer than 5 days, a catheter specimen of urine on day 5 was used to determine the day 5 reading. All samples were collected via the sampling by standard aseptic procedure, and sent immediately for port, microbiological investigation. Differences in nosocomial bacteriuria rates were assessed by analysis of variance appropriate for binomial data (logistic regression) using the computer programme GLIM.’ Of the 182 patients (100 male, 82 female) who were admitted to the study, 83 were randomly assigned to active treatment and 99 to control. The age of these patients ranged from 24-98 years (mean 72.9 years). Of the 182 patients admitted to the study, 130 (71.4%) had a sterile urine on first examination at the time of catheterization and 34 (26.2%) of these developed catheter-associated bacteriuria during the five days following catheterization. The overall bacteriuria rate among controls (35.2%) was used as a baseline for calculating an adjusted bacteriuria rate among the Silverline patients. This computation took into account the differences between centres and sexes as determined by logistic regression analysis. The adjusted bacteriuria rate when the Silverline device was in use was 16*4%, a reduction in the overall incidence of nosocomial catheter-associated bacteriuria of 53 % . There was no significant interaction between treatment and centre (P= 0.6) or between treatment and sex (P= O-2). In other words, the treatment effect was consistent between centres and between sexes. The presence of organisms in a catheter system frequently represents colonization rather than infection. Nevertheless, presence of bacteria remains potentially harmful. Another problem allied to catheter-associated bacteria is their ability to form a biofilm, namely a population of microorganisms and their extracellular products bound to a solid surface. Ramsay et aL9 demonstrated the presence of biofilms on 16 out of 33 urethral catheters removed from an unselected group of hospitalized patients. Biofilms were observed on all types of catheter material examined, including latex, silicone elastomer, solid silicone, PVC and Teflon coated latex. Whilst bladder washouts and various types of antiseptics have been widely used in an attempt to control bacteriuria in patients with long-term indwelling catheters, recent studies have suggested that although bacteria such as Escherichia coli may be inhibited in the urine, they may persist in the
156
Letters
to the Editor
biofilm and perpetuate the cycle of infection.” Thus the possibility of preventing the initiation of such a cycle by the constant release of silver ions is attractive. In comparison with a visually identical placebo, the device that we tested reduced nosocomial urinary tract bacteriuria by 53 % (P= 0.028) in the population studied. Its routine use as a prophylactic measure has the potential to improve the health care of short-term catheterized patients and to reduce hospital costs. Furthermore, it has the potential to be used in areas such as orthopaedic prosthetic surgery where catheter-associated bacteraemia may be disastrous. We gratefully
acknowledge
the assistance
of Mr
P. Royston
E. L. Teare” H. Lewit A. Peacock* S. Marshall* M. Norton1 M. B. Robertsong D. Mackg J. Fultons
with
the statistical
analysis.
“Public Health Laboratory, New Writtle Street, Chelnasford; Essex CM2 0 YX; tBroom$eld Hospital, Chelmsford; $Princess Alexandra Hospital, Harlow; &S’tobhill Hospital, Glasgow
References 1. Currie E, Maynard A. The economics of hospital acquired infection. Discussion Paper 56. Centre for health economics, University of York 1989. 2. Garibaldi RA, Burke JP, Dickman ML, Smith CB. Factors predisposing to bacteriuria during indwelling urethral catheterisation. N Engl J Med 1974; 291: 215-219. 3. Vollaard EJ, Clasener HAL, Zambin JV, Joosten HJM, Van Griethuysen AJA. Prevention of catheter-associated Gram-negative bacilluria with norfloxacin by selective decontamination of the bowel and high urinary concentration. J Antimicrob Chemother 1989; 24: 915-922. 4. Stamm WE. Guidelines for prevention of catheter-associated urinary tract infections. Ann Intern Med 1975; 82: 386-390. 5. Kunin CM. Detection, Prevention and Management of Urinary Tract Infections. 4th Edn. Philadelphia, PA: Lea & Febinger 1987. ” 6. Platt R. Polk BF. Murdock B. Rosner B. Mortalitv associated with nosocomial urinarv tract infection. k EnglJ Med’1982; 307: 637-642.7. Gilchrist T, Healy DM, Drake C. Controlled silver-releasing polymers and their potential for urinary infection control. Biomaterials 1991; 12: 76-78. 8. Baker RT. Nelder TA. The GLIM ,&stem. Release 3.77. Oxford: Numerical Algorithms Group i&35. ” 9. Ramsay JW, Garnham AJ, Mulhall AB, Crow RA, Bryan JM, Eardley I, Vale JA, Whitfield HN. Biofilms. bacteria and bladder catheters. A clinical studv. Bri 7 Ural 1989; 64: 395-398. 10. Stickler D, Dolman J, Rolfe S, Chawla J. Activity of antiseptics against Escherichia coli growing as biofilms on silicone surfaces. Eur J Clin Microbial Infect Dis 1989; 8: 974-978.
Letters
to the Editor
References 1. George
JD,
Yates
MD.
Infections
caused
by
opportunistic
mycobacteria:
a review.
r
R
Sot Med 1986: 79: 226-229. 2. Prince DS, Peterson DD, Steiner RM, et al. Infection with Mycobacterium avium complex in patients without predisposing conditions. N EnglJ Med 1989; 321: 863-868. 3. Nunn PP, McAdam KPWJ. Mycobacterial infections and AIDS. Br Med Bull 1988; 44: 801-813. 4. Wallace RJ. Nontuberculous mycobacteria and water: a love affair with increasing clinical importance. Infect Dis Clin North Am 1987; 1: 677-686. 5. Pelletier PA, du Moulin GC, Stottmeier KD. Mycobacteria in public water supplies: comparative resistance to chlorine. Microbial Sci 1988; 5: 147-148. 6. du Moulin GC, Stottmeier KD, Pelletier PA, Tsang, Anna Y, Hedley-Whyte J. Concentration of Mycobacterium avium by hospital hot water systems. JAMA 1988; 260: 1599-1601. 7. Iseman M. Atypical Mycobacterial Diseases. In: Mitchell RS, Petty TL, Schwarz MI, Eds. Synopsis of Clinical Pulmonary Disease, 4th edn. St. Louis: CV. Mosby Company 1989; 85-91. 8. British Society of Gastroenterology. Cleaning and disinfection of equipment for gastrointestinal flexible endoscopy: interim recommendations of a Working Party of the British Society of Gastroenterology. Gut 1988; 29: 113~115 1.
Sir, ‘Silverline’,
a device
for the prevention
of nosocomial
bacteriuria?
Hospital-acquired infections in England have been estimated to ‘have cost the National Health Service more than El14 million in 1987.’ Catheter-associated urinary tract infection is the most common of these, accounting for more than 30% of all reported nosocomial infections.2-4 Nearly 75% of patients with nosocomial urinary tract infection have undergone some form of urological instrumentation, often urinary catheterization, before their infection.5 The prevalence of urinary tract infection increases with the duration of catheterization, which is the predisposing factor most frequently associated with Gram-negative septicaemia and its mortality rate of 20-50°h.6 We have evaluated a device, ‘Silverline’ (Giltech Ltd, Ayrshire, Scotland, UK), consisting of a moulded tube containing a silver-releasing inorganic polymer. When in position, the insert is bathed in urine as it flows to the collection bag and it releases silver ions at a constant rate, for a period of seven days. Biocompatibility studies of the polymer have been undertaken.7 The well-documented broad-spectrum activity of silver7 is claimed to prevent bacteria entering the catheter lumen, to provide an antibacterial internal surface coating on the tubing and to act as a barrier against bacterial contamination following the use of the drainage tap and the sampling port. Patients of either sex who were admitted to the acute medical, surgical or urological wards of three participating hospitals, and who required short-term catheterization (up to 7 days), were included in our evaluation. Ethics committee approval and written informed consent was obtained from
Letters to the Editor
155
all patients. Silver cartridges, or placebo cartridges of identical appearance, were inserted aseptically between the catheter and the drainage bag at the time of catheterization. Patients who had been catheterized before admission to hospital were excluded. For the purpose of this study a catheter-associated bacteriuria was defined as the presence of 10’ cfu ml-’ of bacteria in the urine. Patients who had no bacteria at the first assessment and who subsequently developed growth of 10’ cfu ml-’ urine by day 5 of catheterization were, for the purposes of the study, identified as having a nosocomial bacteriuria. Mid-stream samples of urine were collected before catheterization and on day 5. When a patient remained catheterized for longer than 5 days, a catheter specimen of urine on day 5 was used to determine the day 5 reading. All samples were collected via the sampling by standard aseptic procedure, and sent immediately for port, microbiological investigation. Differences in nosocomial bacteriuria rates were assessed by analysis of variance appropriate for binomial data (logistic regression) using the computer programme GLIM.’ Of the 182 patients (100 male, 82 female) who were admitted to the study, 83 were randomly assigned to active treatment and 99 to control. The age of these patients ranged from 24-98 years (mean 72.9 years). Of the 182 patients admitted to the study, 130 (71.4%) had a sterile urine on first examination at the time of catheterization and 34 (26.2%) of these developed catheter-associated bacteriuria during the five days following catheterization. The overall bacteriuria rate among controls (35.2%) was used as a baseline for calculating an adjusted bacteriuria rate among the Silverline patients. This computation took into account the differences between centres and sexes as determined by logistic regression analysis. The adjusted bacteriuria rate when the Silverline device was in use was 16*4%, a reduction in the overall incidence of nosocomial catheter-associated bacteriuria of 53 % . There was no significant interaction between treatment and centre (P= 0.6) or between treatment and sex (P= O-2). In other words, the treatment effect was consistent between centres and between sexes. The presence of organisms in a catheter system frequently represents colonization rather than infection. Nevertheless, presence of bacteria remains potentially harmful. Another problem allied to catheter-associated bacteria is their ability to form a biofilm, namely a population of microorganisms and their extracellular products bound to a solid surface. Ramsay et aL9 demonstrated the presence of biofilms on 16 out of 33 urethral catheters removed from an unselected group of hospitalized patients. Biofilms were observed on all types of catheter material examined, including latex, silicone elastomer, solid silicone, PVC and Teflon coated latex. Whilst bladder washouts and various types of antiseptics have been widely used in an attempt to control bacteriuria in patients with long-term indwelling catheters, recent studies have suggested that although bacteria such as Escherichia coli may be inhibited in the urine, they may persist in the
156
Letters
to the Editor
biofilm and perpetuate the cycle of infection.” Thus the possibility of preventing the initiation of such a cycle by the constant release of silver ions is attractive. In comparison with a visually identical placebo, the device that we tested reduced nosocomial urinary tract bacteriuria by 53 % (P= 0.028) in the population studied. Its routine use as a prophylactic measure has the potential to improve the health care of short-term catheterized patients and to reduce hospital costs. Furthermore, it has the potential to be used in areas such as orthopaedic prosthetic surgery where catheter-associated bacteraemia may be disastrous. We gratefully
acknowledge
the assistance
of Mr
P. Royston
E. L. Teare” H. Lewit A. Peacock* S. Marshall* M. Norton1 M. B. Robertsong D. Mackg J. Fultons
with
the statistical
analysis.
“Public Health Laboratory, New Writtle Street, Chelnasford; Essex CM2 0 YX; tBroom$eld Hospital, Chelmsford; $Princess Alexandra Hospital, Harlow; &S’tobhill Hospital, Glasgow
References 1. Currie E, Maynard A. The economics of hospital acquired infection. Discussion Paper 56. Centre for health economics, University of York 1989. 2. Garibaldi RA, Burke JP, Dickman ML, Smith CB. Factors predisposing to bacteriuria during indwelling urethral catheterisation. N Engl J Med 1974; 291: 215-219. 3. Vollaard EJ, Clasener HAL, Zambin JV, Joosten HJM, Van Griethuysen AJA. Prevention of catheter-associated Gram-negative bacilluria with norfloxacin by selective decontamination of the bowel and high urinary concentration. J Antimicrob Chemother 1989; 24: 915-922. 4. Stamm WE. Guidelines for prevention of catheter-associated urinary tract infections. Ann Intern Med 1975; 82: 386-390. 5. Kunin CM. Detection, Prevention and Management of Urinary Tract Infections. 4th Edn. Philadelphia, PA: Lea & Febinger 1987. ” 6. Platt R. Polk BF. Murdock B. Rosner B. Mortalitv associated with nosocomial urinarv tract infection. k EnglJ Med’1982; 307: 637-642.7. Gilchrist T, Healy DM, Drake C. Controlled silver-releasing polymers and their potential for urinary infection control. Biomaterials 1991; 12: 76-78. 8. Baker RT. Nelder TA. The GLIM ,&stem. Release 3.77. Oxford: Numerical Algorithms Group i&35. ” 9. Ramsay JW, Garnham AJ, Mulhall AB, Crow RA, Bryan JM, Eardley I, Vale JA, Whitfield HN. Biofilms. bacteria and bladder catheters. A clinical studv. Bri 7 Ural 1989; 64: 395-398. 10. Stickler D, Dolman J, Rolfe S, Chawla J. Activity of antiseptics against Escherichia coli growing as biofilms on silicone surfaces. Eur J Clin Microbial Infect Dis 1989; 8: 974-978.
