- Email: [email protected]
Levels of microbial contamination on surgical instruments
L e v e l s of m i c r o b i a l c o n t a m i n a t i o n on surgical instruments William A. Rutala, PhD, MPH ",b Maria E Gergen, MT(ASCP) c Jessie F. Jones c David J. Weber, MD, MPH a,b Chapel Hill, North Carolina
Objective: To ascertain the microbial load and type of organisms on used surgical instruments following standard cleaning, which consisted of the use of a washer sterilizer followed by sonic cleaning. Design: In this prospective experimental study, used surgical instruments were immersed in Peptamin Tween broth, the broth agitated, and then filtered through a 0.45 ~tm filter. Quantitative cultures were performed, and all microbes were identified by using standard techniques. Setting: This study was conducted at a 660-bed university hospital. Results: The microbial load remaining on used surgical instruments after cleaning was as follows: 36 (72%) instruments 0 to 10 colony-forming units (CFU), 7 (14%) instruments 11 to 100 CFU, and 7 (14%) instruments >100 CFU. Organisms contaminating the instruments included coagulase-negative staphylococcus (56%) followed by Bacillus (22%) and diphtheroids (14%). No other microbes were isolated from more than 4% of the instruments. Conclusion: Most used nonlumen surgical instruments contain less than I00 CFU of relatively nonpathogenic microorganisms after cleaning. This suggests that new lowtemperature sterilization technologies are likely to be highly effective in preventing cross-transmission of infection via nonlumen medical instruments. (AJ1C Am J Infect Control 1998;26:143-5.)
Surgical instruments are considered critical i t e m s if t h e y e n t e r sterile tissue. Critical i t e m s s h o u l d b e sterile w h e n u s e d b e c a u s e of t h e h i g h r i s k of i n f e c t i o n if s u c h a n i t e m is c o n t a m i n a t e d with any microorganism, including bacterial spores. Although surgical equipment commonly is s t e r i l i z e d b y s t e a m s t e r i l i z a t i o n , e t h y l e n e o x i d e a l s o is u s e d . Until r e c e n t l y t h e e t h y l e n e o x i d e s t e r i l i z e r s u s e d in t h e U n i t e d S t a t e s c o m bined ethylene oxide with a chlorofluorocarbon carrier. H o w e v e r , u n d e r t h e C l e a n Air Act, chlor o f l u o r o c a r b o n w a s e l i m i n a t e d in 1995 b e c a u s e o f s c i e n t i f i c e v i d e n c e l i n k i n g it to d e s t r u c t i o n o f
t h e e a r t h ' s o z o n e layer. A l t e r n a t i v e t e c h n o l o g i e s to e t h y l e n e o x i d e w i t h a c h l o r o f l u o r o c a r b o n c a r r i e r i n c l u d e e t h y l e n e o x i d e w i t h a d i f f e r e n t stab i l i z i n g g a s (eg, c a r b o n d i o x i d e , h y d r o c h l o r o f l u orocarbon), vaporized hydrogen peroxide, gas p l a s m a s , o z o n e , a n d c h l o r i n e dioxide. H o w e v e r , these new technologies may have a lower margin o f s a f e t y t h a n s t e a m s t e r i l i z a t i o n . B e c a u s e t h e level o f m i c r o b i a l c o n t a m i n a t i o n o f t h e o b j e c t to b e s t e r i l i z e d p l a y s s u c h a c r u cial r o l e in d e t e r m i n i n g t h e e f f i c a c y o f t h e o v e r all s t e r i l i z a t i o n p r o c e s s , w e e v a l u a t e d t h e microbial load on used surgical instruments b e f o r e s t e r i l i z a t i o n . L2
From the Division of Infectious Diseases, University of North Carolina School of Medicinef and the Departments of Hospital Epidemiologyb and Surgical Services, ~ University of North Carolina Hospitals, Chapel Hill.
METHODS
Reprint requests: William A. Rutala, PhD, MPH, 547 BurnettWomack Building, CB #7030, Division of Infectious Diseases, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7030. Copyright 9 1998 by the Association for Professionals in Infection Control and Epidemiology, Inc. 0196-6553/98 $5.00 + 0
17/47/83694
This s t u d y w a s c o n d u c t e d at the U n i v e r s i t y of N o r t h C a r o l i n a H o s p i t a l s , a 660-bed a c a d e m i c facility. E x p e r i m e n t s w e r e c o n d u c t e d in July 1996. A v a r i e t y o f s t a i n l e s s steel s u r g i c a l i n s t r u ments were chosen, including retractors, c l a m p s , s p e c u l a , s u c t i o n tips, c a l i p e r s , pliers, a n d k n i f e h a n d l e s . T h e s e i n s t r u m e n t s all w e r e u s e d in the o p e r a t i n g r o o m s o f the U n i v e r s i t y o f N o r t h C a r o l i n a H o s p i t a l s . A f t e r u s e in s u r g i c a l 143
AJIC 144
Rutala et al.
April 1998
Fig. 1. Representative instruments sampled in this study. From left, they include large Deaver retractor, blue clip, 9 in curved Metzenbaum, medium Richardson retractor, #3 knife handle, vein retractor, blunt Rake retractor, long spongestick clamp, 7 in DeBakey forceps, and Weitlander retractor.
T a b l e 1. Microbial load on used surgical instruments after cleaning but before sterilization Percentage of instruments with colony counts Number of operations
25
Number of instruments
50
T a b l e 2. Microbes contaminating used surgical instruments Microbe
0-10 CFU
11-100 CFU
>100 CFU
72
14
14
procedures, the i n s t r u m e n t s were placed in a washer sterilizer and sonically cleaned, and t h e n placed in a milk b a t h for lubrication. A phenolic was added to the milk bath to reduce potential c o n t a m i n a t i o n . I n s t r u m e n t s then were packaged for sterilization in the i n s t r u m e n t preparation area, which is adjacent to the operating rooms. Packaged i n s t r u m e n t s were t r a n s p o r t e d to the Hospital Epidemiology laboratory and u n w r a p p e d in an aseptic manner. I n s t r u m e n t s were i m m e r s e d in P e p t a m i n b r o t h (Difco Laboratories, Detroit, Mich.) to which Tween-80 was added. The broth and i n s t r u m e n t were agitated on a shaker at 150 rpm. After 30 m i n u t e s of agitation, the broth was filtered t h r o u g h a disposable 0.45 gm cellulosic m e m b r a n e filter unit (MSI Savur, Westboro, Maine). The filter was washed with 100 mL sterile water and placed on a TSA (BBL, Cockeysville, Maryland) plate. Plates were incubated at 37 ~ C for 48 hours. Any colonies t h a t appeared on the filter were e n u m e r a t e d and identified by Gram's stain,
Coagulase negative staphylococcus Bacillus sp Bacillus cereus Diphtheroids Propionibacterium sp Alcaligenes xylosoxidans subsp xylosoxidans Stenotrophomonas maltophilia Micrococcus sp
Percentage of instruments contaminated
56 16 6 14 2 4
4 4
API 50 CH, API NFT, or API 20E (bioMerieux Vitek Inc., Hazelwood, Mo.). RESULTS
Fifty surgical instruments were obtained from 25 operations. These 25 operations included these sites or types: abdominal 10, thyroid or lymph node 6, orthopedic 3, plastic 3, vascular 1, chest 1, and gynecologic 1. Fig. 1 depicts a representative group of instruments. A p p r o x i m a t e l y 70% of the used i n s t r u m e n t s o b t a i n e d after c l e a n i n g were c o n t a m i n a t e d w i t h 10 or less c o l o n y f o r m i n g u n i t s (CFU)(Table 1). F o u r t e e n p e r c e n t were contam i n a t e d with 11 to 100 CFU a n d 14% were c o n t a m i n a t e d w i t h g r e a t e r t h a n 100 CFU. Overall, 30% of the i n s t r u m e n t s yielded no
AJIC
Rutala et al. 1 4 5
Volume 26, Number 2
growth. In only t w o cases did i n s t r u m e n t s yield t o o m a n y colonies to count. In b o t h of these cases, the c o n t a m i n a t i n g o r g a n i s m was coagulase-negative s t a p h y l o c o c c u s . The most c o m m o n contaminating organism was coagulase-negative staphylococcus followed by Bacillus sp, diphtheroids, Alcaligenes xylosoxidans s u b s p xylosoxidans, Stenotrophomonas maltophilia, Micrococcus sp, and Propionibacterium sp (Table 2). DISCUSSION
The data revealed that the microbial load on used surgical instruments following standard cleaning was low; 72% of instruments had 0 to 10 CFU and only 4% exceeded 425 CFU. In the only other study of c o n t a m i n a t i o n levels on used surgical instruments, N y s t r o m r e p o r t e d that 60% of instruments carried <101 organisms, 80% <102 organisms, and 90% <103 organisms. 3 Further, w h e t h e r the operations were clean, clean-contaminated, contaminated, or dirty did not significantly affect the microbial load. D e c o n t a m i n a t i o n of u s e d surgical instrum e n t s is r e c o m m e n d e d for two reasons. First, it p r o t e c t s the staff handling the i n s t r u m e n t s from acquiring infection in the event of a perc u t a n e o u s injury. Second, it r e d u c e s the bioburden as well as residual protein and salt before sterilization and t h e r e b y enhances the reliability of the sterilization process. In general, surgical i n s t r u m e n t s that are used on sterile b o d y tissues are c o n t a m i n a t e d with low levels of m i c r o b e s (ie, 90% have b i o b u r d e n <103). 3 The b i o b u r d e n on rigid e n d o s c o p e s after use has been r e p o r t e d to range from 101 to 104 CFU p e r device. 4 In contrast, the b i o b u r d e n in the channels of flexible e n d o s c o p e s has been reported as 7.0 x 109.5 Studies of clinically used e n d o s c o p e s and experimentally c o n t a m i n a t e d e n d o s c o p e s have d e m o n s t r a t e d that cleaning r e m o v e d 4 logs of microorganisms. 5,6 For these reasons, d e c o n t a m i n a t i o n / c l e a n i n g is universally recomm e n d e d as a key c o m p o n e n t of sterilization and disinfection processes. 7 Current sterilization guidelines r e c o m m e n d that b e c a u s e of the risk of cross-infection, all critical items (ie, items that contact a sterile tissue) should be sterilized b e t w e e n patient uses. 7 Sterilization processes must be cleared by the F o o d and Drug Administration (FDA) before entering clinical practice in the United States. For a sterilization process to be cleared by the FDA, it m u s t pass simulated-use testing, which
includes these requirements: the articles selected for each material should exhibit design configurations that provide the greatest challenge to the penetration of the sterilant (eg, lumens), the test article m u s t be i n o c u l a t e d with >106 CFU/unit, the most resistant test organism must be used, an organic load must be present, the inocula must be allowed to dry, and the inocula must be placed on various locations on the test article, including those least favorable to penetration and to contact with the sterilant. 8 Not surprisingly, all currently available low-temperature sterilization processes m a y fail u n d e r these stringent test conditions. 1 It has been argued that the FDA r e q u i r e m e n t s are too stringent and do not reflect clinical practice. 2 Our data and that of N y s t r o m 3 suggest that properly cleaned n o n l u m e n used surgical i n s t r u m e n t s carry a low b i o b u r d e n of organisms that are relatively nonpathogenic. For this reason, new l o w - t e m p e r a t u r e sterilization technologies are likely to be highly effective in preventing cross-transmission of infection via n o n l u m e n medical instruments. The FDA s h o u l d b a s e its test p a r a m e t e r s for approval of sterilization processes on scientifically o b t a i n e d and clinically relevant data. References 1. Alfa MJ, DeGagne P, Olson N, Puchalski T. Comparison of ion plasma, vaporized hydrogen peroxide, and 100% ethylene oxide sterilizers to the 12/88 ethylene oxide gas sterilizer. Infect Control Hosp Epidemiol 1996;17:92-100. 2. Rutala WA, Weber DJ. Low-temperature sterilization technologies: do we need to redefine "sterilization"? Infect Control Hosp Epidemiol 1996;17:87-91. 3. Nystrom B. Disinfection of surgical instruments. J Hosp Infect 1981 ;2:363-8. 4. Chan-Myers H, McAlister D, Antonoplos P. Natural bioburden levels detected on rigid lumened medical devices before and after cleaning [Abstract]. AJIC Am J Infect Control 1997;25:185. 5. Chu NS, McAlister D, Antonoplos PA. Natural bioburden levels detected on flexible gastrointestinal endoscopes after clinical use and following manual cleaning [Abstract]. AJIC Am J Infect Control 1997;25:186. 6. Rutala WA, Weber DJ. FDA labeling requirements for disinfection of endoscopes: a counterpoint. Infect Control Hosp Epidemiol 1995;16:231-5. 7. Rutala WA and APIC Guidelines Committee. APIC guideline for selection and use of disinfectants. AJIC Am J Infect Control 1996;24:313-42. 8. Food and Drug Administration, Division of General and Restorative Devices. Guidance on premarket notification (510k) submissions for sterilizers intended for use in health care facilities. Washington: FDA; March 1993.
Objective: To ascertain the microbial load and type of organisms on used surgical instruments following standard cleaning, which consisted of the use of a washer sterilizer followed by sonic cleaning. Design: In this prospective experimental study, used surgical instruments were immersed in Peptamin Tween broth, the broth agitated, and then filtered through a 0.45 ~tm filter. Quantitative cultures were performed, and all microbes were identified by using standard techniques. Setting: This study was conducted at a 660-bed university hospital. Results: The microbial load remaining on used surgical instruments after cleaning was as follows: 36 (72%) instruments 0 to 10 colony-forming units (CFU), 7 (14%) instruments 11 to 100 CFU, and 7 (14%) instruments >100 CFU. Organisms contaminating the instruments included coagulase-negative staphylococcus (56%) followed by Bacillus (22%) and diphtheroids (14%). No other microbes were isolated from more than 4% of the instruments. Conclusion: Most used nonlumen surgical instruments contain less than I00 CFU of relatively nonpathogenic microorganisms after cleaning. This suggests that new lowtemperature sterilization technologies are likely to be highly effective in preventing cross-transmission of infection via nonlumen medical instruments. (AJ1C Am J Infect Control 1998;26:143-5.)
Surgical instruments are considered critical i t e m s if t h e y e n t e r sterile tissue. Critical i t e m s s h o u l d b e sterile w h e n u s e d b e c a u s e of t h e h i g h r i s k of i n f e c t i o n if s u c h a n i t e m is c o n t a m i n a t e d with any microorganism, including bacterial spores. Although surgical equipment commonly is s t e r i l i z e d b y s t e a m s t e r i l i z a t i o n , e t h y l e n e o x i d e a l s o is u s e d . Until r e c e n t l y t h e e t h y l e n e o x i d e s t e r i l i z e r s u s e d in t h e U n i t e d S t a t e s c o m bined ethylene oxide with a chlorofluorocarbon carrier. H o w e v e r , u n d e r t h e C l e a n Air Act, chlor o f l u o r o c a r b o n w a s e l i m i n a t e d in 1995 b e c a u s e o f s c i e n t i f i c e v i d e n c e l i n k i n g it to d e s t r u c t i o n o f
t h e e a r t h ' s o z o n e layer. A l t e r n a t i v e t e c h n o l o g i e s to e t h y l e n e o x i d e w i t h a c h l o r o f l u o r o c a r b o n c a r r i e r i n c l u d e e t h y l e n e o x i d e w i t h a d i f f e r e n t stab i l i z i n g g a s (eg, c a r b o n d i o x i d e , h y d r o c h l o r o f l u orocarbon), vaporized hydrogen peroxide, gas p l a s m a s , o z o n e , a n d c h l o r i n e dioxide. H o w e v e r , these new technologies may have a lower margin o f s a f e t y t h a n s t e a m s t e r i l i z a t i o n . B e c a u s e t h e level o f m i c r o b i a l c o n t a m i n a t i o n o f t h e o b j e c t to b e s t e r i l i z e d p l a y s s u c h a c r u cial r o l e in d e t e r m i n i n g t h e e f f i c a c y o f t h e o v e r all s t e r i l i z a t i o n p r o c e s s , w e e v a l u a t e d t h e microbial load on used surgical instruments b e f o r e s t e r i l i z a t i o n . L2
From the Division of Infectious Diseases, University of North Carolina School of Medicinef and the Departments of Hospital Epidemiologyb and Surgical Services, ~ University of North Carolina Hospitals, Chapel Hill.
METHODS
Reprint requests: William A. Rutala, PhD, MPH, 547 BurnettWomack Building, CB #7030, Division of Infectious Diseases, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7030. Copyright 9 1998 by the Association for Professionals in Infection Control and Epidemiology, Inc. 0196-6553/98 $5.00 + 0
17/47/83694
This s t u d y w a s c o n d u c t e d at the U n i v e r s i t y of N o r t h C a r o l i n a H o s p i t a l s , a 660-bed a c a d e m i c facility. E x p e r i m e n t s w e r e c o n d u c t e d in July 1996. A v a r i e t y o f s t a i n l e s s steel s u r g i c a l i n s t r u ments were chosen, including retractors, c l a m p s , s p e c u l a , s u c t i o n tips, c a l i p e r s , pliers, a n d k n i f e h a n d l e s . T h e s e i n s t r u m e n t s all w e r e u s e d in the o p e r a t i n g r o o m s o f the U n i v e r s i t y o f N o r t h C a r o l i n a H o s p i t a l s . A f t e r u s e in s u r g i c a l 143
AJIC 144
Rutala et al.
April 1998
Fig. 1. Representative instruments sampled in this study. From left, they include large Deaver retractor, blue clip, 9 in curved Metzenbaum, medium Richardson retractor, #3 knife handle, vein retractor, blunt Rake retractor, long spongestick clamp, 7 in DeBakey forceps, and Weitlander retractor.
T a b l e 1. Microbial load on used surgical instruments after cleaning but before sterilization Percentage of instruments with colony counts Number of operations
25
Number of instruments
50
T a b l e 2. Microbes contaminating used surgical instruments Microbe
0-10 CFU
11-100 CFU
>100 CFU
72
14
14
procedures, the i n s t r u m e n t s were placed in a washer sterilizer and sonically cleaned, and t h e n placed in a milk b a t h for lubrication. A phenolic was added to the milk bath to reduce potential c o n t a m i n a t i o n . I n s t r u m e n t s then were packaged for sterilization in the i n s t r u m e n t preparation area, which is adjacent to the operating rooms. Packaged i n s t r u m e n t s were t r a n s p o r t e d to the Hospital Epidemiology laboratory and u n w r a p p e d in an aseptic manner. I n s t r u m e n t s were i m m e r s e d in P e p t a m i n b r o t h (Difco Laboratories, Detroit, Mich.) to which Tween-80 was added. The broth and i n s t r u m e n t were agitated on a shaker at 150 rpm. After 30 m i n u t e s of agitation, the broth was filtered t h r o u g h a disposable 0.45 gm cellulosic m e m b r a n e filter unit (MSI Savur, Westboro, Maine). The filter was washed with 100 mL sterile water and placed on a TSA (BBL, Cockeysville, Maryland) plate. Plates were incubated at 37 ~ C for 48 hours. Any colonies t h a t appeared on the filter were e n u m e r a t e d and identified by Gram's stain,
Coagulase negative staphylococcus Bacillus sp Bacillus cereus Diphtheroids Propionibacterium sp Alcaligenes xylosoxidans subsp xylosoxidans Stenotrophomonas maltophilia Micrococcus sp
Percentage of instruments contaminated
56 16 6 14 2 4
4 4
API 50 CH, API NFT, or API 20E (bioMerieux Vitek Inc., Hazelwood, Mo.). RESULTS
Fifty surgical instruments were obtained from 25 operations. These 25 operations included these sites or types: abdominal 10, thyroid or lymph node 6, orthopedic 3, plastic 3, vascular 1, chest 1, and gynecologic 1. Fig. 1 depicts a representative group of instruments. A p p r o x i m a t e l y 70% of the used i n s t r u m e n t s o b t a i n e d after c l e a n i n g were c o n t a m i n a t e d w i t h 10 or less c o l o n y f o r m i n g u n i t s (CFU)(Table 1). F o u r t e e n p e r c e n t were contam i n a t e d with 11 to 100 CFU a n d 14% were c o n t a m i n a t e d w i t h g r e a t e r t h a n 100 CFU. Overall, 30% of the i n s t r u m e n t s yielded no
AJIC
Rutala et al. 1 4 5
Volume 26, Number 2
growth. In only t w o cases did i n s t r u m e n t s yield t o o m a n y colonies to count. In b o t h of these cases, the c o n t a m i n a t i n g o r g a n i s m was coagulase-negative s t a p h y l o c o c c u s . The most c o m m o n contaminating organism was coagulase-negative staphylococcus followed by Bacillus sp, diphtheroids, Alcaligenes xylosoxidans s u b s p xylosoxidans, Stenotrophomonas maltophilia, Micrococcus sp, and Propionibacterium sp (Table 2). DISCUSSION
The data revealed that the microbial load on used surgical instruments following standard cleaning was low; 72% of instruments had 0 to 10 CFU and only 4% exceeded 425 CFU. In the only other study of c o n t a m i n a t i o n levels on used surgical instruments, N y s t r o m r e p o r t e d that 60% of instruments carried <101 organisms, 80% <102 organisms, and 90% <103 organisms. 3 Further, w h e t h e r the operations were clean, clean-contaminated, contaminated, or dirty did not significantly affect the microbial load. D e c o n t a m i n a t i o n of u s e d surgical instrum e n t s is r e c o m m e n d e d for two reasons. First, it p r o t e c t s the staff handling the i n s t r u m e n t s from acquiring infection in the event of a perc u t a n e o u s injury. Second, it r e d u c e s the bioburden as well as residual protein and salt before sterilization and t h e r e b y enhances the reliability of the sterilization process. In general, surgical i n s t r u m e n t s that are used on sterile b o d y tissues are c o n t a m i n a t e d with low levels of m i c r o b e s (ie, 90% have b i o b u r d e n <103). 3 The b i o b u r d e n on rigid e n d o s c o p e s after use has been r e p o r t e d to range from 101 to 104 CFU p e r device. 4 In contrast, the b i o b u r d e n in the channels of flexible e n d o s c o p e s has been reported as 7.0 x 109.5 Studies of clinically used e n d o s c o p e s and experimentally c o n t a m i n a t e d e n d o s c o p e s have d e m o n s t r a t e d that cleaning r e m o v e d 4 logs of microorganisms. 5,6 For these reasons, d e c o n t a m i n a t i o n / c l e a n i n g is universally recomm e n d e d as a key c o m p o n e n t of sterilization and disinfection processes. 7 Current sterilization guidelines r e c o m m e n d that b e c a u s e of the risk of cross-infection, all critical items (ie, items that contact a sterile tissue) should be sterilized b e t w e e n patient uses. 7 Sterilization processes must be cleared by the F o o d and Drug Administration (FDA) before entering clinical practice in the United States. For a sterilization process to be cleared by the FDA, it m u s t pass simulated-use testing, which
includes these requirements: the articles selected for each material should exhibit design configurations that provide the greatest challenge to the penetration of the sterilant (eg, lumens), the test article m u s t be i n o c u l a t e d with >106 CFU/unit, the most resistant test organism must be used, an organic load must be present, the inocula must be allowed to dry, and the inocula must be placed on various locations on the test article, including those least favorable to penetration and to contact with the sterilant. 8 Not surprisingly, all currently available low-temperature sterilization processes m a y fail u n d e r these stringent test conditions. 1 It has been argued that the FDA r e q u i r e m e n t s are too stringent and do not reflect clinical practice. 2 Our data and that of N y s t r o m 3 suggest that properly cleaned n o n l u m e n used surgical i n s t r u m e n t s carry a low b i o b u r d e n of organisms that are relatively nonpathogenic. For this reason, new l o w - t e m p e r a t u r e sterilization technologies are likely to be highly effective in preventing cross-transmission of infection via n o n l u m e n medical instruments. The FDA s h o u l d b a s e its test p a r a m e t e r s for approval of sterilization processes on scientifically o b t a i n e d and clinically relevant data. References 1. Alfa MJ, DeGagne P, Olson N, Puchalski T. Comparison of ion plasma, vaporized hydrogen peroxide, and 100% ethylene oxide sterilizers to the 12/88 ethylene oxide gas sterilizer. Infect Control Hosp Epidemiol 1996;17:92-100. 2. Rutala WA, Weber DJ. Low-temperature sterilization technologies: do we need to redefine "sterilization"? Infect Control Hosp Epidemiol 1996;17:87-91. 3. Nystrom B. Disinfection of surgical instruments. J Hosp Infect 1981 ;2:363-8. 4. Chan-Myers H, McAlister D, Antonoplos P. Natural bioburden levels detected on rigid lumened medical devices before and after cleaning [Abstract]. AJIC Am J Infect Control 1997;25:185. 5. Chu NS, McAlister D, Antonoplos PA. Natural bioburden levels detected on flexible gastrointestinal endoscopes after clinical use and following manual cleaning [Abstract]. AJIC Am J Infect Control 1997;25:186. 6. Rutala WA, Weber DJ. FDA labeling requirements for disinfection of endoscopes: a counterpoint. Infect Control Hosp Epidemiol 1995;16:231-5. 7. Rutala WA and APIC Guidelines Committee. APIC guideline for selection and use of disinfectants. AJIC Am J Infect Control 1996;24:313-42. 8. Food and Drug Administration, Division of General and Restorative Devices. Guidance on premarket notification (510k) submissions for sterilizers intended for use in health care facilities. Washington: FDA; March 1993.