Journal
of Hospital
Infection
(1991)
19, 167-l
74
Bacterial contamination of air and surgical wounds during joint replacement operations. Comparison of two different types of staff clothing J. H.
Department
Scheibel,
Ingrid
Jensen
and Susanne
Pedersen
of Clinical Microbiology, Copenhagen County Hospitals, DK-2730 Herlev, Denmark Accepted for publication
16 September 1991
Summary:
Compared with conventional surgical clothing, polypropylene coveralls reduced the bacterial contamination of the air of a conventionally ventilated operating room by 62%. The contamination of surgical wounds during joint replacement was also reduced, but not to a significant degree. Sixteen percent of the bacteria sampled from the wounds were resistant to the prophylactic antibiotic and the importance of a clean air system for performing joint replacement operations is stressed. The use of commercially available non-woven swabs for sampling bacteria from the surgical wound compared favourably with the use of specially prepared velvet pads.
Keywords:
Surgical
clothing;
wound
sampling;
bacterial
contamination;
joint
replacement.
Introduction
Bacteriologically clean air has been shown to reduce postoperative joint sepsis in patients undergoing joint replacement operations,’ and it has been suggested that the average concentration of airborne bacteria-carrying particles should not exceed 10 m -3 .2 This low level of air contamination can be obtained in ultraclean air systems, but it has also been obtained in a conventionally ventilated operating room by dressing the staff in polypropylene coveralls. 3 The coveralls are now commercially available, and the aim of this study was to evaluate whether the polypropylene coveralls, when used in daily practice, could reduce the bacterial contamination of the air and the wound in a conventionally ventilated operating room to a level comparable to that obtained by ultraclean air systems. In addition, two different methods for sampling bacteria from the operation wound were compared.
0195-6701/91/110167+08
SO3.00/0
0 1991 The Hospital
167
Infection
Society
168
J. H. Scheibel Material
et al.
and methods
Material During a 3-month period patients undergoing elective total hip or knee replacement, performed in a single operating room in a university hospital, were entered in the study. As far as possible the patients were entered consecutively, but practical reasons necessitated exclusion of a few operations. Exclusion of an operation always took place before randomization. All patients had antibiotic prophylaxis with cefuroxime 1.5 g immediately prior to commencing the operation. Randomization and staJg-clothing The operations were allocated at random to two different regimens. Immediately before the operation, an envelope was opened determining whether either cotton/polyester clothing or the polypropylene coveralls should be used. The cotton/polyester clothing consisted of conventional short-sleeved shirts and trousers or for the female staff sometimes a dress. The polypropylene coveralls were a short-sleeved whole-body suit close-fitting at ankles and arms (Klinidress, Molnlycke, Sweden). All personnel present in the operating room used the same kind of dress. Except for the clothing worn, all other conditions were identical. Non-woven drapes, surgical gowns and hoods were used for all operations. The doors to the operation room were locked during the procedure. One of the authors was present during the operations to perform bacteriological sampling. Bacterial sampling from the air A centrifugal sampler (Biotest ‘HYCON,’ Biotest-Serum-Institut, Frankfurt/Main, West Germany) was used. Sampling was performed five times during each operation: during unpacking of the instruments and placing them on the instrument table, during incision of the skin, during sawing of the bone, during insertion of the prosthesis and during closure of the wound. Sampling took place as close to the wound as possible, the distance being c. 75 cm. Each sampling lasted four minutes. The agar strips were incubated at 35°C for 48 h and the colony count was converted into colony forming units per cubic metre (cfu rne3) according to the manufacturer’s manual. Bacterial sampling from sedimentation plates Sedimentation plates (9 cm blood plates) were placed in duplicate on tables close to the instrument table and on the opposite side of the operating table. The plates close to the instrument table were exposed only during the period when the instruments were uncovered, and the other two plates were exposed from the time of wound incision to the time of wound closure. All plates were incubated at 35°C for 48 h.
Bacterial
contamination
of joint
replacements
169
Bacterial sampling from the wound Before closure of the wound, sampling from the subcutaneous tissue was performed using pads as described by Raahave4 as well as non-woven swabs (Mesoft, Molnlycke, Sweden). The sizes of pad and swab were 10 cm* and 25 cm*, respectively. Two pads and two swabs were used for each wound. The pads and swabs were moistened with saline, gently pressed against different parts of the subcutaneous tissues of the wounds and then transferred to two bottles, each containing 100 ml of saline, one for the pads and one for the swabs. Immediately after the operation, the bottles were shaken vigorously for 5 min and the contents of each bottle filtered through a sterile 0.45 pm filter (ME 25/21, Schleicher & Schuell), which was then placed on a blood agar plate and incubated aerobically at 35°C for 48 h.
Bacteriological methods The numbers of cfus from wound samples and sedimentation plates were counted and colonies showing differences in appearance were identified using standard methods. Micrococcus spp. were separated from the staphylococci by means of resistance to furazolidone. Susceptibility to novobiocin was used to divide the coagulase-negative staphylococci into Staphylococcus epidermidis and Staphylococcus saprophyticus. Susceptibility testing for cefuroxime and methicillin was performed using a disc diffusion method (Biodisk AB, Solna, Sweden). The resistance of staphylococci to methicillin was determined on salt agar at 30°C. Staphylococci resistant to methicillin were regarded as also resistant to cefuroxime. Up to five different colony types, appearing in greatest number, were identified for each sedimentation plate. From wound samples all colonies showing differences in appearance were identified.
Statistical methods The MEDSTAT statistical programme for the analysis of the results of controlled therapeutic trials was used. 5 The test groups were compared by non-parametric methods (Mann-Whitney test for unpaired data, and Wilcoxon-Pratt test for paired data). In addition, Fisher’s exact test was used.
Results
Forty-six operations on 46 patients constituted the material of the study. Twenty-three operations were randomized to the group in which conventional cotton/polyester clothing was used, and 23 were assigned to the group in which the polypropylene coveralls were used. Table I shows that the two groups of operations were comparable regarding relevant
J. H. Scheibel
170 Table
I.
al.
et
Characteristics
of
operations
Conventional polyester
cotton/ dress
Polypropylene coveralls
of operations
23
23
No. of knee-replacements/ no. of hip-replacements
6117
7116
No.
Duration median
of operations-minutes (range)
Time during which uncovered-minutes median (range) No. of persons median (range)
the
instruments
119.7
(50-160)
115.0
(65-190)
130.0
(85-180)
134.8
(87-218)
were
present
6.2 (6-7)
6.4 (6-8)
parameters. Also, the ratio of female to male participants was the same in the two groups. Table II shows that the use of polypropylene coveralls resulted in a significant reduction in the bacterial contamination of the air during all phases of the operation. The overall reduction amounted to 62%. The bacterial content of the air was lower during unpacking of the instruments than during the operative procedure, presumably due to the fact that fewer persons were present in the operating room. During the operation the bacterial content of the air remained constant when using the conventional dress, but increased during the period between primary incision and closure of the wound in the group using polypropylene coveralls (P=O*O4). Table III shows that there was a significant reduction in the number of bacteria on the sedimentation plates when the polypropylene coveralls were worn. In contrast to the sedimentation plates near the operating table, the plates on the instrument table were exposed also during unpacking of the instruments, when the air contamination was lower than during the surgical procedure; this may, at least in part, explain the difference between the number of bacteria at the two locations. Four of the wounds in the cotton/polyester group and five of the wounds in the polypropylene groups were sterile; this difference was not significant. The pads and the swabs used for wound sampling yielded growth from the same number of wounds (Table IV). A comparison of the methods showed no significant difference in the number of bacteria sampled (P= O-3). The median value for positive pads was 10.4 cfu 100 cme2 (range S-1210) and for positive swabs 14.0 cfu 100 cmP2 (range 2-340). Table V shows the dominance of bacterial species, presumably originating from the skin, in both the wounds and on the sedimentation plates. The distribution of species and susceptibility patterns was similar in
Bacterial Table
II.
contamination
of joint
Procedure performed while sampling
cfu mm3(range)
Conventional cotton/polyester dress
Unpacking the instruments Incision Sawing the bone Insertion of prosthesis Closure of the wound Mean value for each operation
III.
118.8 168.8 156.0 168.8 156.3 158.6
Polypropylene coveralls
(25-356) (31-+81) (255463) (19-575) (S&438) (49-394)
31.3 44.0 62.3 56.3 81.0 60.3
Number of bacteria on sedimentation
Instrument (N=42)
Polypropylene
P value * Not
coveralls
642.0 276.6
table
Operating (N=46)
(81-1730)
1090.4
(81-694)
528.0
< 0~0001
Reduction (%)
(G175) (t&l 69) (G694) (&363) (133225) (10-221)
P-value
74 74 40 67 48 62
< 0~0001 < 0~0001 0.0004 0.0016 0.0007 < 0~0001
plates and in the wounds
Sedimentation plates Median cfu m-* h-’ (range)
Conventional cotton/ polyester dress
171
Number of bacteria in the air during total joint replacement Median
Table
replacements
Wound samples Median (cfu per wound) (range) table (N=46)
(308-2456)
5.7 (&42)
(61551)
2.3 (t&412)
< 0~0001
0.37*
significant
Table
Comparison ojpads and swabs for sampling of surgical wounds
IV.
Both negative Only pads negative Only swabs negative Both positive No. of wounds (patients)
9
examined
i 22 46
the two groups, except for micrococci and corynebacteria, which seemed to appear in greater numbers in the wounds than in the air. Sixteen percent of bacteria from the wounds were resistant to cefuroxime. Discussion
Improvements in surgical asepsis are of course expected to result in a decline in the number of postoperative wound infections. However, the rate
172 Table
J. H. V.
Scheibel
et al.
Number and sensitivity of aerobic bacterial species obtainedfrom from sedimentation plates Wound
Staphylococcus aureus
surgical wounds and
Sedimentation
1 v9*
1 (0)
S. epidermidis
41 (3)
54 (2)
S. saprophyticus
12 (8)
16 (9)
Coagulase-negative further speciated
Micrococcus
spp.
Corynebacterium Others** Total
Staphylococcus
spp.
plates
not
2 (0)
6 (2)
11 (3)
3 (0)
16 (0)
3 (0)
4 (0)
3 (2)
87 (14)
86 (15)
* In parenthesis: number resistant to methicillin/cefuroxime. ** Neirseria spp., Gram-negative rods (not Enterobacteriaceae).
of postoperative infections after joint replacement is so small that an unrealistically large sample size is required to detect a practicably attainable decrease. Fortunately, there is a well-documented relationship between the level of air contamination, contamination of the wound and development of wound infection,‘j so that measuring the two first-mentioned parameters is an acceptable substitute for recording of wound infections. The centrifugal air sampler is convenient to use and the consistency of the instrument has been found satisfactory.7 However, conversion of centrifugal sampler counts to cfu mP3 may yield values higher than those obtained by a slit air sampler.8 We found a 62% reduction in the bacterial contamination of the air of the operation room from 159 cfu m-3 to 60 cfu rnd3 when the’ staff were dressed in polypropylene coveralls instead of conventional cotton/polyester clothing. However, our data suggest a decline in the bacteria-retaining property of the polypropylene clothing during the surgical procedure. The reduction in air contamination found by us is far less than that found by Bergman et aZ.3 who compared a prototype of the same polypropylene suit and conventional cotton clothing. In a conventionally ventilated operating room they found an average of 8 cfu mP3 when the polypropylene suit was used and an average of 170 cfu mP3 when conventional cotton clothing was used, corresponding to a reduction of 95 %. The reason for this discrepancy in results is not clear. The use of different air sampling equipment hardly explains the difference in reduction of air contamination. Bergman et aZ.3 compared the polypropylene coveralls with cotton clothing while we compared them with cotton/polyester clothing. However, there are scarc,ely
Bacterial
contamination
of joint
replacements
173
significant differences in the ability of the two types of clothing to retain microorganisms.’ It is possible that during the process of developing the commercial suit changes have been made in the polypropylene clothing so that it now differs from the prototype used by Bergman et ~1.~ The reduction in air contamination found by us is comparable to that already found in conventionally ventilated operating rooms by comparing cotton clothing with non-woven trousers (43-6O%‘s) or by comparing cotton clothing with specially prepared polyester clothing (76%“). Two methods for bacteriological sampling from the wound were compared. The velvet pads are rather time-consuming to prepare, and commercially available non-woven swabs appear to work just as well. However, the two methods should be compared on rnore surgical wounds, including contaminated wounds with higher bacterial density. The bacterial contamination of the wounds was not reduced significantly when the two types of clothing were compared. The surgical wound is not solely exposed to bacterial contamination by direct sedimentation from the air. It has been suggested that although at least 95% of bacteria in the patient’s wound come from the air in the conventionally ventilated operating room, the majority of the organisms do not fall directly from the air into the wound but fall on to other surfaces (e.g. instruments) and are transferred indirectly to the wound. ‘* However, the wound is also exposed to contamination from other sources. Bacterial particles may be rubbed through the clothing, especially when it is damp, and contamination of surgical clothing or gloves may be transferred directly or indirectly to the wound. The patient’s skin may be a source of contamination, and on occasions when there is a high level of skin carriage, the wound may be grossly contaminated. l2 Minor reductions in air contamination are thus not always reflected in the contamination of the wound. Prophylactic perioperative antibiotics can reduce the incidence of deep joint sepsis to an extent comparable to that obtained by the use of clean air systems. ‘al3 There is however, no perfect universal antibiotic, and our finding of a rate of resistance to cefuroxime (the antibiotic given) of 16% is disquieting. It is not likely that the high incidence of resistant bacteria found in the wound is due to selection caused by antibiotic content in the wound fluid, since the same incidence of resistant bacteria was found on the sedimentation plates. Susceptibility testing in the microbiological laboratory is designed to guide the treatment of infections and is not necessarily equally effective in predicting the effect of the prophylactic use of antibiotics. Nevertheless, it is most likely that a relationship exists between the rate of susceptible bacteria in the wound and the effect of the antibiotic given, i.e. the risk of development of wound sepsis. The inability to predict to what extent an antibiotic used for prophylaxis maintains its effect is a major argument for using measures that effectively reduce the bacterial contamination of the wound. Furthermore, it is likely that there is an additive beneficial effect on
174
J. H. Scheibel
et al.
the rate of joint sepsis, both by reducing the bacterial contamination of the air and by using antibiotics6 The present data do not indicate that the use of specially prepared operation suits, including polypropylene coveralls, renders a clean air system superfluous. A clean air system should be regarded as a basic requirement for performing joint-replacement operations and presumably also for some other operations where the introduction of a foreign body renders them more susceptible to infection. Prophylactic antibiotics and bacteria-tight clothing might serve as supplements to this basic requirement. We thank the staff of the orthopaedic department at Copenhagen for allowing us to conduct these experiments during their surgical supported by Sygekassernes Helsefond, grant no. H 1 l/101-87.
County operations.
Hospital, This
Herlev, study was
References 1. Lidwell OM, Lowbury EJL, Whyte W, Blowers R, Stanley SJ, Lowe D. Effect of ultraclean air in operating rooms on deep sepsis in the joint after total hip or knee replacement: a randomised study. Br MedJ 1982; 285: l&14. Whyte W, Lidwell OM, Lowbury EJL, Blowers R. Suggested bacteriological standards for air in ultraclean operating rooms. J Hosp Infect 1983; 4: 133-139. Bergman BR, Hoborn J, Nachemson AL. Patient draping and staff clothing in the operating theatre: a microbiological study. ScandJ Infect Dis 1985; 17: 421426. Raahave D, Friis-Maller A. Velvet pad surface sampling of aerobic and anaerobic bacteria: An in-vitro laboratory model. J Clin Pathol 1982; 35: 13561360. Wulff HR, Schlichting P. Statistical program for the analyses of the results of controlled therapeutic trials and other types of clinical research. ASTRA Group A/S, DK-2620 Albertslund, 1988. 6. Lidwell OM. Air, antibiotics and sepsis in replacement joints. J Hosp Znfect 1988; 11 (Suppl. C): 1840. 7. Casewell MW, Desai N, Lease EJ. The use of the Reuter centrifugal air sampler for the estimation of bacterial air counts in different hospital locations. J Hosp Infect 1986; 7: 250-260. 8. Nackhla LS, Cummings RF. A comparative evaluation of a new centrifugal air sampler (RCS) with a slit air sampler (SAS) in a hospital environment. J Hosp Znfect 1981; 2: 261-266. 9. Schwartz JT, Saunders DE. Microbial penetration of surgical gown materials. Surg Gynecol Obstet 1980; 150: 507-512. IO. Whyte W, Hodgson R, Bailey PV, Graham J. The reduction of bacteria in the operation room through the use of non-woven clothing. BY J Surg 1978; 65: 469474. 11. Whyte W, Hamblen DL, Kelly IG, Hambraeus A, Laurel1 G. An investigation of occlusive polyester surgical clothing. J Hasp Infect 1990; 15: 363-374. 12. Whyte W, Hodgson R, Tinkler J. The importance of airborne bacterial contamination of wounds. J Hosp Znfect 1982; 3: 123-135. F, Flamant R, Evrard J. Prophylactic cefazolin versus placebo in total hip 13. Hill C, Mazas replacement. Lancet 1981; 1: 795-797.
of Hospital
Infection
(1991)
19, 167-l
74
Bacterial contamination of air and surgical wounds during joint replacement operations. Comparison of two different types of staff clothing J. H.
Department
Scheibel,
Ingrid
Jensen
and Susanne
Pedersen
of Clinical Microbiology, Copenhagen County Hospitals, DK-2730 Herlev, Denmark Accepted for publication
16 September 1991
Summary:
Compared with conventional surgical clothing, polypropylene coveralls reduced the bacterial contamination of the air of a conventionally ventilated operating room by 62%. The contamination of surgical wounds during joint replacement was also reduced, but not to a significant degree. Sixteen percent of the bacteria sampled from the wounds were resistant to the prophylactic antibiotic and the importance of a clean air system for performing joint replacement operations is stressed. The use of commercially available non-woven swabs for sampling bacteria from the surgical wound compared favourably with the use of specially prepared velvet pads.
Keywords:
Surgical
clothing;
wound
sampling;
bacterial
contamination;
joint
replacement.
Introduction
Bacteriologically clean air has been shown to reduce postoperative joint sepsis in patients undergoing joint replacement operations,’ and it has been suggested that the average concentration of airborne bacteria-carrying particles should not exceed 10 m -3 .2 This low level of air contamination can be obtained in ultraclean air systems, but it has also been obtained in a conventionally ventilated operating room by dressing the staff in polypropylene coveralls. 3 The coveralls are now commercially available, and the aim of this study was to evaluate whether the polypropylene coveralls, when used in daily practice, could reduce the bacterial contamination of the air and the wound in a conventionally ventilated operating room to a level comparable to that obtained by ultraclean air systems. In addition, two different methods for sampling bacteria from the operation wound were compared.
0195-6701/91/110167+08
SO3.00/0
0 1991 The Hospital
167
Infection
Society
168
J. H. Scheibel Material
et al.
and methods
Material During a 3-month period patients undergoing elective total hip or knee replacement, performed in a single operating room in a university hospital, were entered in the study. As far as possible the patients were entered consecutively, but practical reasons necessitated exclusion of a few operations. Exclusion of an operation always took place before randomization. All patients had antibiotic prophylaxis with cefuroxime 1.5 g immediately prior to commencing the operation. Randomization and staJg-clothing The operations were allocated at random to two different regimens. Immediately before the operation, an envelope was opened determining whether either cotton/polyester clothing or the polypropylene coveralls should be used. The cotton/polyester clothing consisted of conventional short-sleeved shirts and trousers or for the female staff sometimes a dress. The polypropylene coveralls were a short-sleeved whole-body suit close-fitting at ankles and arms (Klinidress, Molnlycke, Sweden). All personnel present in the operating room used the same kind of dress. Except for the clothing worn, all other conditions were identical. Non-woven drapes, surgical gowns and hoods were used for all operations. The doors to the operation room were locked during the procedure. One of the authors was present during the operations to perform bacteriological sampling. Bacterial sampling from the air A centrifugal sampler (Biotest ‘HYCON,’ Biotest-Serum-Institut, Frankfurt/Main, West Germany) was used. Sampling was performed five times during each operation: during unpacking of the instruments and placing them on the instrument table, during incision of the skin, during sawing of the bone, during insertion of the prosthesis and during closure of the wound. Sampling took place as close to the wound as possible, the distance being c. 75 cm. Each sampling lasted four minutes. The agar strips were incubated at 35°C for 48 h and the colony count was converted into colony forming units per cubic metre (cfu rne3) according to the manufacturer’s manual. Bacterial sampling from sedimentation plates Sedimentation plates (9 cm blood plates) were placed in duplicate on tables close to the instrument table and on the opposite side of the operating table. The plates close to the instrument table were exposed only during the period when the instruments were uncovered, and the other two plates were exposed from the time of wound incision to the time of wound closure. All plates were incubated at 35°C for 48 h.
Bacterial
contamination
of joint
replacements
169
Bacterial sampling from the wound Before closure of the wound, sampling from the subcutaneous tissue was performed using pads as described by Raahave4 as well as non-woven swabs (Mesoft, Molnlycke, Sweden). The sizes of pad and swab were 10 cm* and 25 cm*, respectively. Two pads and two swabs were used for each wound. The pads and swabs were moistened with saline, gently pressed against different parts of the subcutaneous tissues of the wounds and then transferred to two bottles, each containing 100 ml of saline, one for the pads and one for the swabs. Immediately after the operation, the bottles were shaken vigorously for 5 min and the contents of each bottle filtered through a sterile 0.45 pm filter (ME 25/21, Schleicher & Schuell), which was then placed on a blood agar plate and incubated aerobically at 35°C for 48 h.
Bacteriological methods The numbers of cfus from wound samples and sedimentation plates were counted and colonies showing differences in appearance were identified using standard methods. Micrococcus spp. were separated from the staphylococci by means of resistance to furazolidone. Susceptibility to novobiocin was used to divide the coagulase-negative staphylococci into Staphylococcus epidermidis and Staphylococcus saprophyticus. Susceptibility testing for cefuroxime and methicillin was performed using a disc diffusion method (Biodisk AB, Solna, Sweden). The resistance of staphylococci to methicillin was determined on salt agar at 30°C. Staphylococci resistant to methicillin were regarded as also resistant to cefuroxime. Up to five different colony types, appearing in greatest number, were identified for each sedimentation plate. From wound samples all colonies showing differences in appearance were identified.
Statistical methods The MEDSTAT statistical programme for the analysis of the results of controlled therapeutic trials was used. 5 The test groups were compared by non-parametric methods (Mann-Whitney test for unpaired data, and Wilcoxon-Pratt test for paired data). In addition, Fisher’s exact test was used.
Results
Forty-six operations on 46 patients constituted the material of the study. Twenty-three operations were randomized to the group in which conventional cotton/polyester clothing was used, and 23 were assigned to the group in which the polypropylene coveralls were used. Table I shows that the two groups of operations were comparable regarding relevant
J. H. Scheibel
170 Table
I.
al.
et
Characteristics
of
operations
Conventional polyester
cotton/ dress
Polypropylene coveralls
of operations
23
23
No. of knee-replacements/ no. of hip-replacements
6117
7116
No.
Duration median
of operations-minutes (range)
Time during which uncovered-minutes median (range) No. of persons median (range)
the
instruments
119.7
(50-160)
115.0
(65-190)
130.0
(85-180)
134.8
(87-218)
were
present
6.2 (6-7)
6.4 (6-8)
parameters. Also, the ratio of female to male participants was the same in the two groups. Table II shows that the use of polypropylene coveralls resulted in a significant reduction in the bacterial contamination of the air during all phases of the operation. The overall reduction amounted to 62%. The bacterial content of the air was lower during unpacking of the instruments than during the operative procedure, presumably due to the fact that fewer persons were present in the operating room. During the operation the bacterial content of the air remained constant when using the conventional dress, but increased during the period between primary incision and closure of the wound in the group using polypropylene coveralls (P=O*O4). Table III shows that there was a significant reduction in the number of bacteria on the sedimentation plates when the polypropylene coveralls were worn. In contrast to the sedimentation plates near the operating table, the plates on the instrument table were exposed also during unpacking of the instruments, when the air contamination was lower than during the surgical procedure; this may, at least in part, explain the difference between the number of bacteria at the two locations. Four of the wounds in the cotton/polyester group and five of the wounds in the polypropylene groups were sterile; this difference was not significant. The pads and the swabs used for wound sampling yielded growth from the same number of wounds (Table IV). A comparison of the methods showed no significant difference in the number of bacteria sampled (P= O-3). The median value for positive pads was 10.4 cfu 100 cme2 (range S-1210) and for positive swabs 14.0 cfu 100 cmP2 (range 2-340). Table V shows the dominance of bacterial species, presumably originating from the skin, in both the wounds and on the sedimentation plates. The distribution of species and susceptibility patterns was similar in
Bacterial Table
II.
contamination
of joint
Procedure performed while sampling
cfu mm3(range)
Conventional cotton/polyester dress
Unpacking the instruments Incision Sawing the bone Insertion of prosthesis Closure of the wound Mean value for each operation
III.
118.8 168.8 156.0 168.8 156.3 158.6
Polypropylene coveralls
(25-356) (31-+81) (255463) (19-575) (S&438) (49-394)
31.3 44.0 62.3 56.3 81.0 60.3
Number of bacteria on sedimentation
Instrument (N=42)
Polypropylene
P value * Not
coveralls
642.0 276.6
table
Operating (N=46)
(81-1730)
1090.4
(81-694)
528.0
< 0~0001
Reduction (%)
(G175) (t&l 69) (G694) (&363) (133225) (10-221)
P-value
74 74 40 67 48 62
< 0~0001 < 0~0001 0.0004 0.0016 0.0007 < 0~0001
plates and in the wounds
Sedimentation plates Median cfu m-* h-’ (range)
Conventional cotton/ polyester dress
171
Number of bacteria in the air during total joint replacement Median
Table
replacements
Wound samples Median (cfu per wound) (range) table (N=46)
(308-2456)
5.7 (&42)
(61551)
2.3 (t&412)
< 0~0001
0.37*
significant
Table
Comparison ojpads and swabs for sampling of surgical wounds
IV.
Both negative Only pads negative Only swabs negative Both positive No. of wounds (patients)
9
examined
i 22 46
the two groups, except for micrococci and corynebacteria, which seemed to appear in greater numbers in the wounds than in the air. Sixteen percent of bacteria from the wounds were resistant to cefuroxime. Discussion
Improvements in surgical asepsis are of course expected to result in a decline in the number of postoperative wound infections. However, the rate
172 Table
J. H. V.
Scheibel
et al.
Number and sensitivity of aerobic bacterial species obtainedfrom from sedimentation plates Wound
Staphylococcus aureus
surgical wounds and
Sedimentation
1 v9*
1 (0)
S. epidermidis
41 (3)
54 (2)
S. saprophyticus
12 (8)
16 (9)
Coagulase-negative further speciated
Micrococcus
spp.
Corynebacterium Others** Total
Staphylococcus
spp.
plates
not
2 (0)
6 (2)
11 (3)
3 (0)
16 (0)
3 (0)
4 (0)
3 (2)
87 (14)
86 (15)
* In parenthesis: number resistant to methicillin/cefuroxime. ** Neirseria spp., Gram-negative rods (not Enterobacteriaceae).
of postoperative infections after joint replacement is so small that an unrealistically large sample size is required to detect a practicably attainable decrease. Fortunately, there is a well-documented relationship between the level of air contamination, contamination of the wound and development of wound infection,‘j so that measuring the two first-mentioned parameters is an acceptable substitute for recording of wound infections. The centrifugal air sampler is convenient to use and the consistency of the instrument has been found satisfactory.7 However, conversion of centrifugal sampler counts to cfu mP3 may yield values higher than those obtained by a slit air sampler.8 We found a 62% reduction in the bacterial contamination of the air of the operation room from 159 cfu m-3 to 60 cfu rnd3 when the’ staff were dressed in polypropylene coveralls instead of conventional cotton/polyester clothing. However, our data suggest a decline in the bacteria-retaining property of the polypropylene clothing during the surgical procedure. The reduction in air contamination found by us is far less than that found by Bergman et aZ.3 who compared a prototype of the same polypropylene suit and conventional cotton clothing. In a conventionally ventilated operating room they found an average of 8 cfu mP3 when the polypropylene suit was used and an average of 170 cfu mP3 when conventional cotton clothing was used, corresponding to a reduction of 95 %. The reason for this discrepancy in results is not clear. The use of different air sampling equipment hardly explains the difference in reduction of air contamination. Bergman et aZ.3 compared the polypropylene coveralls with cotton clothing while we compared them with cotton/polyester clothing. However, there are scarc,ely
Bacterial
contamination
of joint
replacements
173
significant differences in the ability of the two types of clothing to retain microorganisms.’ It is possible that during the process of developing the commercial suit changes have been made in the polypropylene clothing so that it now differs from the prototype used by Bergman et ~1.~ The reduction in air contamination found by us is comparable to that already found in conventionally ventilated operating rooms by comparing cotton clothing with non-woven trousers (43-6O%‘s) or by comparing cotton clothing with specially prepared polyester clothing (76%“). Two methods for bacteriological sampling from the wound were compared. The velvet pads are rather time-consuming to prepare, and commercially available non-woven swabs appear to work just as well. However, the two methods should be compared on rnore surgical wounds, including contaminated wounds with higher bacterial density. The bacterial contamination of the wounds was not reduced significantly when the two types of clothing were compared. The surgical wound is not solely exposed to bacterial contamination by direct sedimentation from the air. It has been suggested that although at least 95% of bacteria in the patient’s wound come from the air in the conventionally ventilated operating room, the majority of the organisms do not fall directly from the air into the wound but fall on to other surfaces (e.g. instruments) and are transferred indirectly to the wound. ‘* However, the wound is also exposed to contamination from other sources. Bacterial particles may be rubbed through the clothing, especially when it is damp, and contamination of surgical clothing or gloves may be transferred directly or indirectly to the wound. The patient’s skin may be a source of contamination, and on occasions when there is a high level of skin carriage, the wound may be grossly contaminated. l2 Minor reductions in air contamination are thus not always reflected in the contamination of the wound. Prophylactic perioperative antibiotics can reduce the incidence of deep joint sepsis to an extent comparable to that obtained by the use of clean air systems. ‘al3 There is however, no perfect universal antibiotic, and our finding of a rate of resistance to cefuroxime (the antibiotic given) of 16% is disquieting. It is not likely that the high incidence of resistant bacteria found in the wound is due to selection caused by antibiotic content in the wound fluid, since the same incidence of resistant bacteria was found on the sedimentation plates. Susceptibility testing in the microbiological laboratory is designed to guide the treatment of infections and is not necessarily equally effective in predicting the effect of the prophylactic use of antibiotics. Nevertheless, it is most likely that a relationship exists between the rate of susceptible bacteria in the wound and the effect of the antibiotic given, i.e. the risk of development of wound sepsis. The inability to predict to what extent an antibiotic used for prophylaxis maintains its effect is a major argument for using measures that effectively reduce the bacterial contamination of the wound. Furthermore, it is likely that there is an additive beneficial effect on
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the rate of joint sepsis, both by reducing the bacterial contamination of the air and by using antibiotics6 The present data do not indicate that the use of specially prepared operation suits, including polypropylene coveralls, renders a clean air system superfluous. A clean air system should be regarded as a basic requirement for performing joint-replacement operations and presumably also for some other operations where the introduction of a foreign body renders them more susceptible to infection. Prophylactic antibiotics and bacteria-tight clothing might serve as supplements to this basic requirement. We thank the staff of the orthopaedic department at Copenhagen for allowing us to conduct these experiments during their surgical supported by Sygekassernes Helsefond, grant no. H 1 l/101-87.
County operations.
Hospital, This
Herlev, study was
References 1. Lidwell OM, Lowbury EJL, Whyte W, Blowers R, Stanley SJ, Lowe D. Effect of ultraclean air in operating rooms on deep sepsis in the joint after total hip or knee replacement: a randomised study. Br MedJ 1982; 285: l&14. Whyte W, Lidwell OM, Lowbury EJL, Blowers R. Suggested bacteriological standards for air in ultraclean operating rooms. J Hosp Infect 1983; 4: 133-139. Bergman BR, Hoborn J, Nachemson AL. Patient draping and staff clothing in the operating theatre: a microbiological study. ScandJ Infect Dis 1985; 17: 421426. Raahave D, Friis-Maller A. Velvet pad surface sampling of aerobic and anaerobic bacteria: An in-vitro laboratory model. J Clin Pathol 1982; 35: 13561360. Wulff HR, Schlichting P. Statistical program for the analyses of the results of controlled therapeutic trials and other types of clinical research. ASTRA Group A/S, DK-2620 Albertslund, 1988. 6. Lidwell OM. Air, antibiotics and sepsis in replacement joints. J Hosp Znfect 1988; 11 (Suppl. C): 1840. 7. Casewell MW, Desai N, Lease EJ. The use of the Reuter centrifugal air sampler for the estimation of bacterial air counts in different hospital locations. J Hosp Infect 1986; 7: 250-260. 8. Nackhla LS, Cummings RF. A comparative evaluation of a new centrifugal air sampler (RCS) with a slit air sampler (SAS) in a hospital environment. J Hosp Znfect 1981; 2: 261-266. 9. Schwartz JT, Saunders DE. Microbial penetration of surgical gown materials. Surg Gynecol Obstet 1980; 150: 507-512. IO. Whyte W, Hodgson R, Bailey PV, Graham J. The reduction of bacteria in the operation room through the use of non-woven clothing. BY J Surg 1978; 65: 469474. 11. Whyte W, Hamblen DL, Kelly IG, Hambraeus A, Laurel1 G. An investigation of occlusive polyester surgical clothing. J Hasp Infect 1990; 15: 363-374. 12. Whyte W, Hodgson R, Tinkler J. The importance of airborne bacterial contamination of wounds. J Hosp Znfect 1982; 3: 123-135. F, Flamant R, Evrard J. Prophylactic cefazolin versus placebo in total hip 13. Hill C, Mazas replacement. Lancet 1981; 1: 795-797.
