- Email: [email protected]
Evaluation of the Steris System 1 peracetic acid endoscope processor
Journal
of Hospital
Infection
(1995)
29, 143-151
EQUIPMENT
Evaluation
of the Steris Endoscope
C. R. Bradley, Hospital Infection
REPORT
System 1 Peracetic Processor
J. R. Babb
Acid
and G. A. J. Ayliffe
Research Laboratory, City Hospital NHS Road, Birmingham B18 7&H, UK Accepted for publication
Trust, Dudley
30 July 1994
Summary:
An automated endoscope sterilizing machine, the Steris System 1 Processor, was tested for bactericidal and sporicidal efficacy. The disinfectant, peracetic acid, was diluted to 0.2% within an enclosed system. The exposure time to the disinfectant was 12 min and the overall cycle time ranged from 25-38 min, mean 29 min. Preliminary suspension tests, with and without yeast or serum, showed a log,, reduction of >5 with Pseudomonas aeruginosa, Staphylococcus auveus and Bacillus subtilis in 5 min with 0.2% peracetic acid. After a routine cycle in the machine, endoscopes contaminated with the same organisms showed no growth. Two of 24 spore strips, containing lo6 B. subtilis showed a small number of survivors (less than 10 per strip). No significant damage to the endoscope was observed although the number of cycles tested was small (i.e. 31). The advantage of the system is that staff are not directly exposed to the agent,, but the costs per cycle are higher than glutaraldehyde, since peracetic acid IS not renewed. Unlike other automated processers the Steris machine has no cleaning cycle. Keywords:
Endoscope
decontamination;
peracetic
acid.
Introduction
An agent used for disinfection or sterilization of heat-labile endoscopes should be microbiologically effective, non-toxic and non-irritant to staff and should not damage the equipment during processing. Two per cent activated alkaline glutaraldehyde fulfils these requirements apart from an irritant or allergenic effect on staff in direct contact with the solution or with vapours released into the air.’ To counteract these harmful effects, an enclosed system, a fume cupboard or appropriate extraction system is required which can be very expensive.2 Glutaraldehyde shows minimal activity against spores of Bacillus subtilis over a lo-20 min contact period,3 which is a common exposure time for disinfecting invasive endoscopes.4’5 Correspondence Birmingham
B18
0195-6701/95/020143+09
to: J. R. Babb, 7QH, UK.
Hospital
Infection
Research
$08.00/O
Laboratory,
City
Hospital
0 1995 The Hospital
143
NHS
Infection
Trust,
Society
144
C. R. Bradley
Figure
1. The
Steris
System
1 Endoscope
et al.
Processor
and
sterilant
carton
However, there is little evidence of infection from inadequately sterilized endoscopes’ and shorter contact times are often recommended. Autoclaving is preferred to chemical disinfection but is not suitable for flexible endoscopes and some rigid endoscopes. Peracetic acid is a possible alternative to glutaraldehyde for decontamination of heat-labile equipment. It is rapidly sporicidal but it is also toxic and irritant and corrosive to some metals.6 An enclosed system, the Steris System 1 Processor, using 0.2% peracetic acid (Steris 20) as a ‘sterilant’ for endoscopes has been in use in the USA and has received favourable preliminary reports.7’8 A microbiological evaluation of the machine is described in this report. Materials
and methods
Machine and process The Steris System 1 Processor* (see Figure 1) is a bench standing machine with external dimensions of 813 mm wide x 762 mm deep x 813 mm high (with the lid raised) and a weight of 38.6 kg. It is microprocessor controlled * Steris System Yorkshire Y07 USA.
1 Processor marketed in the UK by DiagMed Ltd, Front Street, Norby, Thirsk, 1BE. Manufactured by Steris Corporation, 9450 Pineapple Drive, Mentor, Ohio
North 44060,
Steris
System
1 Processor
145
and the entire decontamination process takes place within an inclined chamber which is secured during a cycle with a lock and an inflatable seal. A 13A po*er supply, mains water and a drain are required. The water used for diluting the disinfectant and rinsing is passed through a bacteria retaining filter (0.22~). Performance of the machine is dependant upon water temperature, pressure and the bacteria retaining filters. A diagnostic cycle can l$ performed at the the start of each session to ensure all services are operational. If a problem occurs, a warning is given on a printout and the machine- will not function. Interchangeable trays are available to permit the processing of up to three rigid endoscopes or one flexible endoscope. Connectorstare available for all-channel irrigation of most types of flexible endoscopes. The endoscopes require thorough manual cleaning before processing since the machine does not have a cleaning function as part of the cycle. The sterilant, 35% peracetic acid, and an anti-corrosive agent, are supplied in a twin compartment sealed single dose carton. The carton is punctured by the user when placed in the machine ready for the next cycle ensuring there is minimal staff exposure to the disinfectant. The concentrated peracetic acid is diluted with filtered mains water at approximately 50°C. The diluted peracetic acid (0.2%) is then circulated within the chamber of the machine and pumped through the channels of the endoscope for 12 min, decontaminating external surfaces, lumens and accessories. It is then discarded to waste and the instruments rinsed four times with filtered (bacteria free) mains water. Clean filtered air is finally passed through the chamber of the machine and the endoscope channels to remove excess water. A printout indicating cycle pass or fail is issued at the end of each cycle.
Microbiological
tests
The bactericidal and sporicidal activity of Steris 20 disinfectant was established using a suspension test with and without the addition of organic matter, i.e. 2% yeast or 10 and 50% horse serum. The test organisms chosen were Pseudomonas aewginosa (NCTC 6749) and Staphylococcus aweus (NCTC 4163) - strains widely used in the Kelsey Sykes disinfectant capacity test. Also used was a spore suspension of Bacillus subtilis var. niger (NCTC 10073) commonly used to validate gaseous sterilization methods. In the absence of an identified neutralizer for peracetic acid, nutrient broth containing 0.75% lecithin and Tween mixture (50 g Tween 80 and 5 g lecithin) was used to recover surviving test organisms. This broth was confirmed as a suitable neutralizing medium by challenging broth containing an equivalent concentration of peracetic acid to that recovered during sampling with low numbers of the test organisms. It was not inhibitory and neutralized disinfectant residues carried over to the recovery system.
146
C. R. Bradley
et al.
In vitro suspension tests One millilitre of overnight broth culture of each of the three test organisms, either with or without the addition of organic soil (i.e. yeast 2%, serum 10 and 50%), was added to 9 ml of freshly prepared 0.2% peracetic acid. The B. subtilis var. niger suspension was heat shocked at 80°C for 1 min to ensure only sporing organisms were used. The ‘sterilant’ was prepared as described in the FDA submission report, i.e. the contents of the Steris 20 carton were carefully removed and added to 6100 ml of water. One millilitre samples were removed from the challenged disinfectant after 30 s, 1, 5, 10 and 30 min time intervals and added to 9 ml of recovery neutralizer broth, mixed well and this and lo-fold dilutions plated onto blood agar. Culture plates were incubated at 37°C for 18 h and surviving test organisms enumerated. The remaining recovery broth was also incubated and examined for turbidity to confirm the total destruction of test organisms. Tests with artijkially contaminated endoscopes The internal channels and external surfaces of a flexible hysteroscope (Stortz), flexible colonoscope CFlO VL (Olympus) and two rigid endoscopes (comprising of catheter, deflecting mechanism, flat valved trocar, trumpet trocar, working element and telescope) were contaminated by painting or irrigating the lumens with suspensions of I? aeruginosa NCTC 6749 or B. subtilis var. niger NCTC 10073 enriched with 10% horse serum. Contaminated instruments were allowed to drain dry for 10 min. The instruments were then sampled to establish the challenge, or pre-disinfection count, or were processed and then sampled to establish the numbers of surviving test organisms. The effectiveness of the machine disinfection or sterilization cycle was then established as the difference between the preand post-disinfection count, i.e. log,, pre-disinfection count - log,, postdisinfection count = log reduction RF. Internal channels were sampled by flushing with 10 ml sterile water from a syringe. Samples were promptly diluted lo-fold in i strength Ringers solution and 0.5 ml of the undiluted recovery fluid and dilutions plated onto blood agar. External surfaces were sampled with swabs and these were also plated onto blood agar. All plates were incubated at 37°C for 18 h and examined for surviving test organisms. Biological monitoring The user instructions mention the recommendations of the Association of the Advancement of Medical Instrumentation (AAMI), i.e. that sterilizers should be tested with a biological monitor at the time of installation and routinely thereafter to assure the effectiveness of the process. No instructions are given on the frequency of testing, the number of spores monitored, or the type of spore, carrier or test piece to be used. B. subtilis var. niger was used in these studies as it is used to monitor ethylene oxide and other chemical sterilization processes. At least a 6 log,, reduction
Steris System
1 Processor
147
in spores is usually required for validation/routine monitoring in the UK and Europe (Health Technical Memorandum 2010 Part 3, 1994, EN 866/ 2, BS EN 550) and elsewhere. On 24 occasions a commercially prepared spore strip (B. subtilis var. niger NCTC 10073, Steriseal Ltd, Redditch, Worcs) meeting DoH specification TSS/S/330.012 and containing lo6 viable spores, was clamped within the sterilizing chamber. On completion of a cycle the spore strips were aseptically transferred into 20 ml of tryptone soya broth. After mixing, 0.5 ml was plated onto blood agar and incubated at 37°C along with the recovery broth which was examined for turbidity for up to 14 days.
Results
Suspension tests - in vitro The bactericidal and sporicidal activity of 0.2% peracetic acid (Steris 20) is shown in Table I. Vegetative bacteria were killed in the presence of 2% yeast within 1 min. The Bacillus spores were more tolerant but were killed in 5 min even in the presence of 50% serum. Acceptable (i.e. >5-6 log,,) reductions were obtained within 5 min for all the test organisms with and without an organic load. The disinfectant contact time within the Steris System 1 Processor is 12 min. Tests with artificially contaminated endoscopes The effectiveness of the Steris System 1 Processor in removing B. subtilis spores and P. aeruginosa from the channels of flexible and rigid endoscopes can be seen in Table II. No surviving test organisms were recovered from the channels of the endoscopes processed. Counts before processing showed a mean of 3.2 x 106. However, the sensitivity of the recovery system did not substantiate complete removal as only 0.5 ml of the 10 ml of recovery broth from the channels was plated out. No organisms were recovered from swabs taken from external surfaces. Tests with spore strips Two of the 24 biological monitors showed growth, surviving spores was small, i.e.
but the number
of
Discussion
Unlike other automated processors’ the Steris System 1 is described as a sterilizer and not a washer disinfector. It was therefore tested for sporicidal as well as bactericidal efficacy.
The
subtilis
log,, reductions
Bacillus
The
times
NIL 2% yeast 10% serum 50% serum
NIL 2% yeast
NIL 2% yeast
load
microbiocidal
Organic
exposure
in-vitro
at different
auveus
I.
Staphylococcus
Table
aeYuginosa
organism
Pseudomonas
Test
cannot
acid
than
7.65 7.65 7.32 7.48
challenge.
5.09 4.95 7.32 4.88
7.26 7.26
7.26
7.26
1 min
7.65 7.65 7.32 7.48
7.26 7.26
7.26
7.26
contact
load
7.32 7.48
10 min
an organic disinfectant
5 min
OY without
at different
tests with reduction
of the initial
3.55 3.39 1.34 1.70
7.26 3.71
7.26
7.26 7.26
7.26
7.26
30 s
Log,,
in suspension
the log,, count
count
peracetic
7.26
log,,
of 0.2%
be greater
Initial
effect
7.32 7.48
30 min
times
%
EL ii; w 5
c,
Steris Table II. Removal the Steris Machine
System
of test microorganisms during a standard
Flexible endoscope Pseudomonas aeYuginosa Rigid endoscope Bacillus subtilis Pseudomonas aeruginosa * The sensitivity those shown.
of the recovery
system
149
from the channels of rigid cycle (i.e. 12 min exposure
Number cycles Flexible hysteroscope Bacillus subtilis Pseudomonas aeruginosa
1 Processor
of
Mean before
log,, count processing
and flexible endoscopes to 0.2% peracetic acid) Mean log,, reduction*
16 19
5.38 7.30
>4.08 .6.00
7
7.61
>6.31
6 24
5.49 6.65
>4.19 P5.35
does not permit
the indication
by
of log reductions
greater
than
The Steris machine does not have a cleansing stage in the cycle. Manual cleaning is recommended prior to all automated processing. However, with other machines, additional cleansing is a component of the cycle. The suspension and endoscope test results indicate that O-2% peracetic acid is a rapidly effective sterilant. The few failures with the commercially prepared biological monitors was surprising but the number of surviving spores was small and at least a 5 log reduction was obtained. This could suggest that the process may be marginal as far as sterilization is concerned when compared with widely accepted sterilization processes, e.g. autoclaving and ethylene oxide. However, in another report on commercial biological monitors,” no survivors of B. subtilis or B. stearothermophilus were obtained in a large number of tests. Peracetic acid (0.2%) would appear to be more rapidly sporicidal than 2% glutaraldehyde3 over a 12-min exposure period and should sterilize cleaned instruments. Although mycobactericidal and virucidal activity were not tested, the rapid sporicidal activity suggests that mycobacteria and most viruses should be similarly killed. The process should therefore be adequate for bronchoscopes. The machine is particularly suitable for sterilizing cystoscopes and surgical or invasive endoscopes, e.g. laparoscopes and arthroscopes. It could also be used for the disinfection, or high grade disinfection, of flexible gastrointestinal endoscopes, but the cycle time of 25-30 min in addition to the time for manual cleansing may be too long for a busy unit. In our tests of 31 cycles, the average cycle length was 29min (range 25-38 min). If disinfection alone is required, consideration might be given to reducing the cycle time by exposing the endoscope to peracetic acid for a much shorter period, i.e. ~5 mins. A chemical agent is of no value if the instrument is damaged during processing. It is claimed that the buffers in this system makes the peracetic
150
C. R. Bradley
et al.
acid virtually inon-corrosive.7 Some damage was sustained to the Stortz hysteroscope and rigid endoscopes used in these studies but it was minimal, i.e. the aluminium anodized coating on the control box became dull and there was some stiffening of the focus mechanisms and some of the valves of the rigid endoscopes. The endoscope manufacturers described these changes as cosmetic and did not consider this to be sufficient to discontinue the process. However, the number of cycles during this evaluation was too few to form an opinion on corrosion or instrument component damage. It is known that peracetic acid is corrosive to some metal? and agreement should be obtained from manufacturers before endoscopes are processed in this manner. Bacteria-free rinse water is required, particularly for invasive endoscopes and bronchoscopes.” In our study, the water supply had a high particle sedimentation index and the inanimate particles rapidly blocked the bacteria retaining filter. The replacement of this filter is costly. A survey of water quality is advised before installation as additional less expensive coarse filters, and possibly a pump, may be required to increase flow and reduce filter exchange frequency. A few other problems occurred initially in the investigation, e.g. low water pressure and temperature, but these were easily corrected. However, it is necessary to ensure that installation is carried out correctly or cycle failures will occur. The pre-session diagnostic check and the cycle printout are particularly useful for detecting operation failures and for quality control and documentation. The single use of the peracetic acid solution substantially increases the cost of a cycle compared with glutaraldehyde, 10 1 of which may be reused for up to 20 times or more in other types of washer/disinfectors.l* However, capital costs may be less, since complete enclosure of peracetic acid within a machine may be less expensive than providing fume cupboards or other air extraction equipment for use with glutaraldehyde. The sterilant concentrate cartons would appear to be safe providing they are stored upright in a cool dry place. Should the carton become damaged toxic peracetic acid could be released. Recently Johnson & Johnson Medical Ltd have introduced an alternative peracetic acid preparation for endoscopes and heat sensitive items. This is described as a stabilized buffered peracetic acid (0.35%) which is claimed will disinfect in 5 min and sterilize in 10 min at room temperature. Preliminary efficacy tests indicate that the performance of this agent is similar to that of Steris 20. The Steris machine is particularly useful for treating non-autoclavable cystoscopes and invasive endoscopes, provided there are no metal parts susceptible to damage by peracetic acid. Thorough pre-cleaning is important as no cleaning cycle is incorporated in the machine. We wish machine.
to thank
DiagMed
Ltd
for
providing
the
disinfectant
and
for
the
loan
of the
Steris
System
1 Processor
151
References 1. Burge PS. Occupational risk of glutaraldehyde. BMJ 1989; 300: 299. 2. Cowan RE, Manning AP, Ayliffe GAJ et al. Aldehyde disinfectants and health in endoscopy units. Gut 1993; 34: 1641-1645. 3. Babb JR, Bradley CR, Ayliffe GAJ. Sporicidal activity of glutaraldehyde and hypochlorites and other factors influencing their selection for the treatment of medical equipment. r Hosp Infect 1980; 1: 63-75. RPD, Feneley RCL, Ayliffe GAJ et al. Decontamination of urological equipment: 4. Cooke Interim report of a Working Group of the Standing Committee on Urological Instruments of the British Association of Urological Surgeons. BrJ Ural 1993; 71: 5-9. 5. Ayliffe GAJ, Babb JR, Bradley CR. Sterilization of arthroscopes and laparoscopes. J Hosp Infect 1992; 22: 265-269. SS. Peroxygen compounds. In: Block SS, Ed. Disinfection, Sterilization and 6. Block Preservation, 4th edn. Philadelphia: Lea & Febiger 1991: 167-181. 7 Crow S. Peracetic acid sterilization: a timely development for a busy healthcare industry. Infect Control Hosp Epidemiol 1992; 13: 111-113. 8. Malcheskv PS. Peracetic acid and its anolication to medical instrument sterilization. Arti$ci& brgans 1993; 17: 147-152. I A 9. Bradley CR. Which machine? Nurs Times 1994; 13: 70-74. 10. Kralovic RC. Use of biological indicators designed for steam or ethylene oxide to monitor a liquid chemical sterilization process. Infect Control Hosp Epidemiol 1993; 14: 313-319. 11. Babb JR. Disinfection and sterilization of endoscopes. Cuvr Opin Infect Dis 1993; 6: 532-537. 12. Babb JR, Bradley CR, Barnes AR. Review of microbicidal activity of glutaraldehyde with progressive dilution in an automated system. (Question & Answer). J Hosp Infect 1992; 20: 51-54.
of Hospital
Infection
(1995)
29, 143-151
EQUIPMENT
Evaluation
of the Steris Endoscope
C. R. Bradley, Hospital Infection
REPORT
System 1 Peracetic Processor
J. R. Babb
Acid
and G. A. J. Ayliffe
Research Laboratory, City Hospital NHS Road, Birmingham B18 7&H, UK Accepted for publication
Trust, Dudley
30 July 1994
Summary:
An automated endoscope sterilizing machine, the Steris System 1 Processor, was tested for bactericidal and sporicidal efficacy. The disinfectant, peracetic acid, was diluted to 0.2% within an enclosed system. The exposure time to the disinfectant was 12 min and the overall cycle time ranged from 25-38 min, mean 29 min. Preliminary suspension tests, with and without yeast or serum, showed a log,, reduction of >5 with Pseudomonas aeruginosa, Staphylococcus auveus and Bacillus subtilis in 5 min with 0.2% peracetic acid. After a routine cycle in the machine, endoscopes contaminated with the same organisms showed no growth. Two of 24 spore strips, containing lo6 B. subtilis showed a small number of survivors (less than 10 per strip). No significant damage to the endoscope was observed although the number of cycles tested was small (i.e. 31). The advantage of the system is that staff are not directly exposed to the agent,, but the costs per cycle are higher than glutaraldehyde, since peracetic acid IS not renewed. Unlike other automated processers the Steris machine has no cleaning cycle. Keywords:
Endoscope
decontamination;
peracetic
acid.
Introduction
An agent used for disinfection or sterilization of heat-labile endoscopes should be microbiologically effective, non-toxic and non-irritant to staff and should not damage the equipment during processing. Two per cent activated alkaline glutaraldehyde fulfils these requirements apart from an irritant or allergenic effect on staff in direct contact with the solution or with vapours released into the air.’ To counteract these harmful effects, an enclosed system, a fume cupboard or appropriate extraction system is required which can be very expensive.2 Glutaraldehyde shows minimal activity against spores of Bacillus subtilis over a lo-20 min contact period,3 which is a common exposure time for disinfecting invasive endoscopes.4’5 Correspondence Birmingham
B18
0195-6701/95/020143+09
to: J. R. Babb, 7QH, UK.
Hospital
Infection
Research
$08.00/O
Laboratory,
City
Hospital
0 1995 The Hospital
143
NHS
Infection
Trust,
Society
144
C. R. Bradley
Figure
1. The
Steris
System
1 Endoscope
et al.
Processor
and
sterilant
carton
However, there is little evidence of infection from inadequately sterilized endoscopes’ and shorter contact times are often recommended. Autoclaving is preferred to chemical disinfection but is not suitable for flexible endoscopes and some rigid endoscopes. Peracetic acid is a possible alternative to glutaraldehyde for decontamination of heat-labile equipment. It is rapidly sporicidal but it is also toxic and irritant and corrosive to some metals.6 An enclosed system, the Steris System 1 Processor, using 0.2% peracetic acid (Steris 20) as a ‘sterilant’ for endoscopes has been in use in the USA and has received favourable preliminary reports.7’8 A microbiological evaluation of the machine is described in this report. Materials
and methods
Machine and process The Steris System 1 Processor* (see Figure 1) is a bench standing machine with external dimensions of 813 mm wide x 762 mm deep x 813 mm high (with the lid raised) and a weight of 38.6 kg. It is microprocessor controlled * Steris System Yorkshire Y07 USA.
1 Processor marketed in the UK by DiagMed Ltd, Front Street, Norby, Thirsk, 1BE. Manufactured by Steris Corporation, 9450 Pineapple Drive, Mentor, Ohio
North 44060,
Steris
System
1 Processor
145
and the entire decontamination process takes place within an inclined chamber which is secured during a cycle with a lock and an inflatable seal. A 13A po*er supply, mains water and a drain are required. The water used for diluting the disinfectant and rinsing is passed through a bacteria retaining filter (0.22~). Performance of the machine is dependant upon water temperature, pressure and the bacteria retaining filters. A diagnostic cycle can l$ performed at the the start of each session to ensure all services are operational. If a problem occurs, a warning is given on a printout and the machine- will not function. Interchangeable trays are available to permit the processing of up to three rigid endoscopes or one flexible endoscope. Connectorstare available for all-channel irrigation of most types of flexible endoscopes. The endoscopes require thorough manual cleaning before processing since the machine does not have a cleaning function as part of the cycle. The sterilant, 35% peracetic acid, and an anti-corrosive agent, are supplied in a twin compartment sealed single dose carton. The carton is punctured by the user when placed in the machine ready for the next cycle ensuring there is minimal staff exposure to the disinfectant. The concentrated peracetic acid is diluted with filtered mains water at approximately 50°C. The diluted peracetic acid (0.2%) is then circulated within the chamber of the machine and pumped through the channels of the endoscope for 12 min, decontaminating external surfaces, lumens and accessories. It is then discarded to waste and the instruments rinsed four times with filtered (bacteria free) mains water. Clean filtered air is finally passed through the chamber of the machine and the endoscope channels to remove excess water. A printout indicating cycle pass or fail is issued at the end of each cycle.
Microbiological
tests
The bactericidal and sporicidal activity of Steris 20 disinfectant was established using a suspension test with and without the addition of organic matter, i.e. 2% yeast or 10 and 50% horse serum. The test organisms chosen were Pseudomonas aewginosa (NCTC 6749) and Staphylococcus aweus (NCTC 4163) - strains widely used in the Kelsey Sykes disinfectant capacity test. Also used was a spore suspension of Bacillus subtilis var. niger (NCTC 10073) commonly used to validate gaseous sterilization methods. In the absence of an identified neutralizer for peracetic acid, nutrient broth containing 0.75% lecithin and Tween mixture (50 g Tween 80 and 5 g lecithin) was used to recover surviving test organisms. This broth was confirmed as a suitable neutralizing medium by challenging broth containing an equivalent concentration of peracetic acid to that recovered during sampling with low numbers of the test organisms. It was not inhibitory and neutralized disinfectant residues carried over to the recovery system.
146
C. R. Bradley
et al.
In vitro suspension tests One millilitre of overnight broth culture of each of the three test organisms, either with or without the addition of organic soil (i.e. yeast 2%, serum 10 and 50%), was added to 9 ml of freshly prepared 0.2% peracetic acid. The B. subtilis var. niger suspension was heat shocked at 80°C for 1 min to ensure only sporing organisms were used. The ‘sterilant’ was prepared as described in the FDA submission report, i.e. the contents of the Steris 20 carton were carefully removed and added to 6100 ml of water. One millilitre samples were removed from the challenged disinfectant after 30 s, 1, 5, 10 and 30 min time intervals and added to 9 ml of recovery neutralizer broth, mixed well and this and lo-fold dilutions plated onto blood agar. Culture plates were incubated at 37°C for 18 h and surviving test organisms enumerated. The remaining recovery broth was also incubated and examined for turbidity to confirm the total destruction of test organisms. Tests with artijkially contaminated endoscopes The internal channels and external surfaces of a flexible hysteroscope (Stortz), flexible colonoscope CFlO VL (Olympus) and two rigid endoscopes (comprising of catheter, deflecting mechanism, flat valved trocar, trumpet trocar, working element and telescope) were contaminated by painting or irrigating the lumens with suspensions of I? aeruginosa NCTC 6749 or B. subtilis var. niger NCTC 10073 enriched with 10% horse serum. Contaminated instruments were allowed to drain dry for 10 min. The instruments were then sampled to establish the challenge, or pre-disinfection count, or were processed and then sampled to establish the numbers of surviving test organisms. The effectiveness of the machine disinfection or sterilization cycle was then established as the difference between the preand post-disinfection count, i.e. log,, pre-disinfection count - log,, postdisinfection count = log reduction RF. Internal channels were sampled by flushing with 10 ml sterile water from a syringe. Samples were promptly diluted lo-fold in i strength Ringers solution and 0.5 ml of the undiluted recovery fluid and dilutions plated onto blood agar. External surfaces were sampled with swabs and these were also plated onto blood agar. All plates were incubated at 37°C for 18 h and examined for surviving test organisms. Biological monitoring The user instructions mention the recommendations of the Association of the Advancement of Medical Instrumentation (AAMI), i.e. that sterilizers should be tested with a biological monitor at the time of installation and routinely thereafter to assure the effectiveness of the process. No instructions are given on the frequency of testing, the number of spores monitored, or the type of spore, carrier or test piece to be used. B. subtilis var. niger was used in these studies as it is used to monitor ethylene oxide and other chemical sterilization processes. At least a 6 log,, reduction
Steris System
1 Processor
147
in spores is usually required for validation/routine monitoring in the UK and Europe (Health Technical Memorandum 2010 Part 3, 1994, EN 866/ 2, BS EN 550) and elsewhere. On 24 occasions a commercially prepared spore strip (B. subtilis var. niger NCTC 10073, Steriseal Ltd, Redditch, Worcs) meeting DoH specification TSS/S/330.012 and containing lo6 viable spores, was clamped within the sterilizing chamber. On completion of a cycle the spore strips were aseptically transferred into 20 ml of tryptone soya broth. After mixing, 0.5 ml was plated onto blood agar and incubated at 37°C along with the recovery broth which was examined for turbidity for up to 14 days.
Results
Suspension tests - in vitro The bactericidal and sporicidal activity of 0.2% peracetic acid (Steris 20) is shown in Table I. Vegetative bacteria were killed in the presence of 2% yeast within 1 min. The Bacillus spores were more tolerant but were killed in 5 min even in the presence of 50% serum. Acceptable (i.e. >5-6 log,,) reductions were obtained within 5 min for all the test organisms with and without an organic load. The disinfectant contact time within the Steris System 1 Processor is 12 min. Tests with artificially contaminated endoscopes The effectiveness of the Steris System 1 Processor in removing B. subtilis spores and P. aeruginosa from the channels of flexible and rigid endoscopes can be seen in Table II. No surviving test organisms were recovered from the channels of the endoscopes processed. Counts before processing showed a mean of 3.2 x 106. However, the sensitivity of the recovery system did not substantiate complete removal as only 0.5 ml of the 10 ml of recovery broth from the channels was plated out. No organisms were recovered from swabs taken from external surfaces. Tests with spore strips Two of the 24 biological monitors showed growth, surviving spores was small, i.e.
but the number
of
Discussion
Unlike other automated processors’ the Steris System 1 is described as a sterilizer and not a washer disinfector. It was therefore tested for sporicidal as well as bactericidal efficacy.
The
subtilis
log,, reductions
Bacillus
The
times
NIL 2% yeast 10% serum 50% serum
NIL 2% yeast
NIL 2% yeast
load
microbiocidal
Organic
exposure
in-vitro
at different
auveus
I.
Staphylococcus
Table
aeYuginosa
organism
Pseudomonas
Test
cannot
acid
than
7.65 7.65 7.32 7.48
challenge.
5.09 4.95 7.32 4.88
7.26 7.26
7.26
7.26
1 min
7.65 7.65 7.32 7.48
7.26 7.26
7.26
7.26
contact
load
7.32 7.48
10 min
an organic disinfectant
5 min
OY without
at different
tests with reduction
of the initial
3.55 3.39 1.34 1.70
7.26 3.71
7.26
7.26 7.26
7.26
7.26
30 s
Log,,
in suspension
the log,, count
count
peracetic
7.26
log,,
of 0.2%
be greater
Initial
effect
7.32 7.48
30 min
times
%
EL ii; w 5
c,
Steris Table II. Removal the Steris Machine
System
of test microorganisms during a standard
Flexible endoscope Pseudomonas aeYuginosa Rigid endoscope Bacillus subtilis Pseudomonas aeruginosa * The sensitivity those shown.
of the recovery
system
149
from the channels of rigid cycle (i.e. 12 min exposure
Number cycles Flexible hysteroscope Bacillus subtilis Pseudomonas aeruginosa
1 Processor
of
Mean before
log,, count processing
and flexible endoscopes to 0.2% peracetic acid) Mean log,, reduction*
16 19
5.38 7.30
>4.08 .6.00
7
7.61
>6.31
6 24
5.49 6.65
>4.19 P5.35
does not permit
the indication
by
of log reductions
greater
than
The Steris machine does not have a cleansing stage in the cycle. Manual cleaning is recommended prior to all automated processing. However, with other machines, additional cleansing is a component of the cycle. The suspension and endoscope test results indicate that O-2% peracetic acid is a rapidly effective sterilant. The few failures with the commercially prepared biological monitors was surprising but the number of surviving spores was small and at least a 5 log reduction was obtained. This could suggest that the process may be marginal as far as sterilization is concerned when compared with widely accepted sterilization processes, e.g. autoclaving and ethylene oxide. However, in another report on commercial biological monitors,” no survivors of B. subtilis or B. stearothermophilus were obtained in a large number of tests. Peracetic acid (0.2%) would appear to be more rapidly sporicidal than 2% glutaraldehyde3 over a 12-min exposure period and should sterilize cleaned instruments. Although mycobactericidal and virucidal activity were not tested, the rapid sporicidal activity suggests that mycobacteria and most viruses should be similarly killed. The process should therefore be adequate for bronchoscopes. The machine is particularly suitable for sterilizing cystoscopes and surgical or invasive endoscopes, e.g. laparoscopes and arthroscopes. It could also be used for the disinfection, or high grade disinfection, of flexible gastrointestinal endoscopes, but the cycle time of 25-30 min in addition to the time for manual cleansing may be too long for a busy unit. In our tests of 31 cycles, the average cycle length was 29min (range 25-38 min). If disinfection alone is required, consideration might be given to reducing the cycle time by exposing the endoscope to peracetic acid for a much shorter period, i.e. ~5 mins. A chemical agent is of no value if the instrument is damaged during processing. It is claimed that the buffers in this system makes the peracetic
150
C. R. Bradley
et al.
acid virtually inon-corrosive.7 Some damage was sustained to the Stortz hysteroscope and rigid endoscopes used in these studies but it was minimal, i.e. the aluminium anodized coating on the control box became dull and there was some stiffening of the focus mechanisms and some of the valves of the rigid endoscopes. The endoscope manufacturers described these changes as cosmetic and did not consider this to be sufficient to discontinue the process. However, the number of cycles during this evaluation was too few to form an opinion on corrosion or instrument component damage. It is known that peracetic acid is corrosive to some metal? and agreement should be obtained from manufacturers before endoscopes are processed in this manner. Bacteria-free rinse water is required, particularly for invasive endoscopes and bronchoscopes.” In our study, the water supply had a high particle sedimentation index and the inanimate particles rapidly blocked the bacteria retaining filter. The replacement of this filter is costly. A survey of water quality is advised before installation as additional less expensive coarse filters, and possibly a pump, may be required to increase flow and reduce filter exchange frequency. A few other problems occurred initially in the investigation, e.g. low water pressure and temperature, but these were easily corrected. However, it is necessary to ensure that installation is carried out correctly or cycle failures will occur. The pre-session diagnostic check and the cycle printout are particularly useful for detecting operation failures and for quality control and documentation. The single use of the peracetic acid solution substantially increases the cost of a cycle compared with glutaraldehyde, 10 1 of which may be reused for up to 20 times or more in other types of washer/disinfectors.l* However, capital costs may be less, since complete enclosure of peracetic acid within a machine may be less expensive than providing fume cupboards or other air extraction equipment for use with glutaraldehyde. The sterilant concentrate cartons would appear to be safe providing they are stored upright in a cool dry place. Should the carton become damaged toxic peracetic acid could be released. Recently Johnson & Johnson Medical Ltd have introduced an alternative peracetic acid preparation for endoscopes and heat sensitive items. This is described as a stabilized buffered peracetic acid (0.35%) which is claimed will disinfect in 5 min and sterilize in 10 min at room temperature. Preliminary efficacy tests indicate that the performance of this agent is similar to that of Steris 20. The Steris machine is particularly useful for treating non-autoclavable cystoscopes and invasive endoscopes, provided there are no metal parts susceptible to damage by peracetic acid. Thorough pre-cleaning is important as no cleaning cycle is incorporated in the machine. We wish machine.
to thank
DiagMed
Ltd
for
providing
the
disinfectant
and
for
the
loan
of the
Steris
System
1 Processor
151
References 1. Burge PS. Occupational risk of glutaraldehyde. BMJ 1989; 300: 299. 2. Cowan RE, Manning AP, Ayliffe GAJ et al. Aldehyde disinfectants and health in endoscopy units. Gut 1993; 34: 1641-1645. 3. Babb JR, Bradley CR, Ayliffe GAJ. Sporicidal activity of glutaraldehyde and hypochlorites and other factors influencing their selection for the treatment of medical equipment. r Hosp Infect 1980; 1: 63-75. RPD, Feneley RCL, Ayliffe GAJ et al. Decontamination of urological equipment: 4. Cooke Interim report of a Working Group of the Standing Committee on Urological Instruments of the British Association of Urological Surgeons. BrJ Ural 1993; 71: 5-9. 5. Ayliffe GAJ, Babb JR, Bradley CR. Sterilization of arthroscopes and laparoscopes. J Hosp Infect 1992; 22: 265-269. SS. Peroxygen compounds. In: Block SS, Ed. Disinfection, Sterilization and 6. Block Preservation, 4th edn. Philadelphia: Lea & Febiger 1991: 167-181. 7 Crow S. Peracetic acid sterilization: a timely development for a busy healthcare industry. Infect Control Hosp Epidemiol 1992; 13: 111-113. 8. Malcheskv PS. Peracetic acid and its anolication to medical instrument sterilization. Arti$ci& brgans 1993; 17: 147-152. I A 9. Bradley CR. Which machine? Nurs Times 1994; 13: 70-74. 10. Kralovic RC. Use of biological indicators designed for steam or ethylene oxide to monitor a liquid chemical sterilization process. Infect Control Hosp Epidemiol 1993; 14: 313-319. 11. Babb JR. Disinfection and sterilization of endoscopes. Cuvr Opin Infect Dis 1993; 6: 532-537. 12. Babb JR, Bradley CR, Barnes AR. Review of microbicidal activity of glutaraldehyde with progressive dilution in an automated system. (Question & Answer). J Hosp Infect 1992; 20: 51-54.