Microbial Load in Septic and Aseptic Procedure Rooms
Results from a prospective, comparative observational study
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Background: Highly effective measures to prevent surgical wound infections have been established over the last two decades. We studied whether the strict separation of septic and aseptic procedure rooms is still necessary.
Methods: In an exploratory, prospective observational study, the microbial concentration in an operating room without a room ventilating system (RVS) was analyzed during 16 septic and 14 aseptic operations with the aid of an air sampler (50 cm and 1 m from the operative field) and sedimentation plates (1 m from the operative field, and contact culture on the walls). The means and standard deviations of the microbial loads were compared with the aid of GEE models (generalized estimation equations).
Results: In the comparison of septic and aseptic operations, no relevant differences were found with respect to the overall microbial concentration in the room air (401.7 ± 176.3 versus 388.2 ± 178.3 CFU/m3; p = 0.692 [CFU, colony-forming units]) or sedimentation 1 m from the operative field (45.3 ± 22.0 versus 48.7 ± 18.5 CFU/m2/min; p = 0.603) and on the walls (35.7 ± 43.7 versus 29.0 ± 49.4 CFU/m2/min; p = 0.685). The only relevant differences between the microbial spectra associated with the two types of procedure were a small amount of sedimentation of Escherichia coli and Enterococcus faecalis in septic operations, and of staphylococcus aureus and pseudomonas stutzeri in aseptic operations, up to 30 minutes after the end of the procedure.
Conclusion: These data do not suggest that septic and aseptic procedure rooms need to be separated. In interpreting the findings, one should recall that the study was not planned as an equivalence or non-inferiority study. Wherever patient safety is concerned, high-level safety concepts should only be demoted to lower levels if new and convincing evidence becomes available.
Germany‘s Accident Insurance Provider for Hospitals (Unfallversicherungsträger für Krankenhäuser) continues to demand that aseptic (noncontaminated or clean contaminated) and septic (contaminated or dirty) surgical procedures be performed in separate locations (1). The recommendation published by the Commission for Hospital Hygiene and Infection Prevention (KRINKO, Kommission für Krankenhaushygiene und Infektionsprävention) of the Robert Koch Institute in 2000, “Surgical Standards” (Anforderungen bei Operationen), divides surgeries by contamination level but does not indicate any possible constructional or organizational consequences of doing so (2). The KRINKO‘s 2007 recommendation on preventing surgical wound infections also makes no mention of the subject of aseptic versus septic procedures (3).
Thanks to technical advances in recent decades, surgical procedure rooms are now almost all fitted with ventilation systems that to a great extent remove pathogens from the operative field (4).
- Preoperative skin antisepsis using alcohol-based preparations that contain a prolonged-action antiseptic ingredient such as chlorhexidine or octenidine and can be applied using mechanical assistance (9, 10).
- No hair removal, or clipping instead of shaving if hair removal is required (11).
- Using two pairs of gloves or changing gloves during surgery (6, 7).
- Appropriate perioperative antibiotic prophylaxis (12, 13).
- Intraoperative normothermia (14, 15).
- Establishing interdisciplinary bundles of measures (8, 16).
- Minimally invasive surgery.
- Hygiene measures implemented within surgical procedure rooms after each procedure.
The changes in surgery conditions call into question whether the requirement for septic and aseptic procedures to be performed in different locations, and for different procedure types to be separated in time by following a set order for surgeries, is still necessary where appropriate ventilation is available and contact transmission via objects or staff members can be ruled out (17–20). This study therefore aimed to investigate, as a worst-case scenario, microbial levels in a surgical procedure room with no ventilation system during both septic and aseptic procedures with no spatial separation or control over the order in which procedures were performed.
A prospective, comparative observational study investigated microbial levels in the air of the procedure room and microbial sedimentation for 16 septic and 14 aseptic procedures within general and visceral surgery (all performed in the same procedure room). Because the study was exploratory in nature, case numbers were not formally calculated in advance. As the study was observational and involved no clinical intervention, the ethical approval of the Ethics Committee of the University of Greifswald was not considered necessary.
For each surgical procedure, surgery type and duration and the number of people present were recorded. The procedure room contained no ventilation system that might affect the outcome parameters. Staff were not informed of the aim of the study. The procedures performed were as follows:
- Eleven aseptic hepatic, pancreatic, and intestinal procedures.
- Three open inguinal hernias.
- Six septic procedures for perforations, ileus, and gallbladder empyema.
- Five jet lavages for massive skin and soft tissue infections.
- Three laparotomies for anastomotic failure, with and without abscesses.
- Two procedures on infected fistulae in Crohn‘s disease.
This range of procedures can be considered typical for visceral surgery.
Measurement of microbial load of procedure room air
The microbial load of the air in the procedure room was determined using an air sampler (IDEAL 3P, bioMérieux SA, Marcy l‘Etoile, France) and agar plates (Columbia agar with 5% sheep blood, diameter 90 mm). According to the information provided by the manufacturer, this sampler measures particles of between 3 and 10 μm and detects 100% of particles measuring 5 μm or more. For each sample, 250 L of air was taken in over a period of 2.5 minutes. A new, sterile measuring head was used for each procedure. The number of colony-forming units (CFUs) detected was calculated using the correction table for the air sampler head used. Air was sampled at 2 locations near to the operating field (N1 and N2, each 50 cm from the operating table) and 2 locations further away (F1 and F2, each 150 cm from the operating table) (Figure). After the procedure room had been prepared (surfaces disinfected, instrument tables brought in) the baseline number of colonies at each sampling location was determined. This was repeated at the following times:
- At the beginning of each procedure (incision).
- Every 30 minutes during procedures.
- At the end of each procedure (closure).
- Thirty minutes after the end of each procedure.
Air colony counts (CFU/m3) at all sampling times and locations were evaluated. This yielded different case numbers according to the duration of the procedure in question.
Recording microbial sedimentation
Sedimentation was investigated for the duration of each procedure (incision to closure) using agar plates at sampling locations S1 and S2 (each 100 cm from the operating field, at the same height as the operating table) (Figure). To evaluate the extent of sedimentation (CFU count), the mean of the findings from the two sampling locations was recorded and the number of CFU/m2/minute was calculated in order to take into account differences in procedure duration.
The microbial load of the procedure room walls was determined on 3 wall surfaces using contact culture plates (Medco contact culture plates mini with sheep blood agar, 55 mm diameter, Medco Diagnostika GmbH, Munich, Germany) (Figure). The contact culture was put in place before the first procedure performed on each day of sampling and at the beginning (incision) and end (closure) of each procedure. Findings are stated in CFU/m2/minute, comparing incision versus closure.
Means and standard deviations of the relevant microbial load parameters were calculated for each of the 2 groups. In order to take account of the unusual structure of the data (multiple samples per procedure), statistical comparison of the 2 groups (septic and aseptic) was performed using GEE (generalized estimating equation) models for continuous outcome parameters in the form of linear regression, assuming normally-distributed residuals and link identity (21). The “exchangeable”-option was chosen as the correlation structure. Whether variables were normally distributed was determined by visual inspection of frequency distributions. Only colony counts obtained using contact cultures showed significant deviation from normal distribution. For these, GEE analyses were replicated using nonparametric tests (Mann-Whitney U-test, no adjustment for data clustering). Analyses were performed using IBM SPSS Statistics, version 22, with a significance level of 0.05 (2-tailed). Because the study was exploratory, no adjustment was performed for multiple tests.
Surgery duration (time from incision to closure) was 70 ± 72.9 minutes for septic procedures (n = 16) and 189 ± 10.2 minutes for aseptic procedures (n = 14) (p <0.001). There was no significant difference in the mean number of persons involved in surgery (7.6 ± 2.1 for septic procedures, 8.1 ± 1.4 for aseptic procedures; p = 0.44).
Microbial load of procedure room air
Quantitative analysis: The baseline microbial load of the air in the procedure room was 98.7 ± 63.96 CFU/m3. There was no statistical evidence of differences between the two groups. This was true for both microbial load throughout surgery up to closure (mean of sum of all individual measurements for septic procedures: 401.7 ± 176.3 CFU/m3; for aseptic procedures: 388.2 ± 178.3 CFU/m3; p = 0.69) (Table 1) and for microbial load 30 minutes after the beginning of procedures, at the end of procedures (closure), and 30 minutes after closure (Table 1). Comparison of the sampling locations near to the operating field (N1, N2) and further from it (F1, F2) also showed no significant differences between the values for septic and aseptic procedures (p = 0.052 and 0.325 respectively).
Qualitative analysis: For both types of procedures the most common pathogens were coagulase-negative staphylococci (CNS), followed by Micrococcus (M.) luteus and aerobic spore-forming bacteria (Table 2). For septic procedures only, Escherichia (E.) coli, Proteus (P.) mirabilis, and Enterococcus (E.) faecalis were found, in addition to skin flora and ubiquitous spore-forming bacteria (n = 22 samples, 4 to 20 CFU/m3 per sample) (Table 2). Thirty minutes after the end of procedures, only E. faecalis (in n = 2 samples, 4 and 8 CFU/m3 respectively) and E. coli (in n = 1 sample, with 4 CFU/m3) were detected. For aseptic procedures only, Staphylococcus (S.) aureus and Pseudomonas (P.) stutzeri (in n = 9 samples, with 4 to 20 CFU/m3 per sample) were detected (Table 2, Table 3). No multiresistant bacteria were found. Substantially more aerobic spore-forming bacteria were released with septic procedures than with aseptic procedures (Table 2).
Quantitative analysis: No significant differences were detected in microbial sedimentation between septic and aseptic procedures at sampling locations S1 or S2 (p = 0.603) (Table 1). There was also no significant difference in the microbial load of the walls (beginning of procedure/incision: p = 0.16, end of procedure/closure: p = 0.69) (Table 1).
Qualitative analysis: At sampling locations S1 and S2, for both types of procedures, CNSs were the most common pathogens, followed by aerobic spore-forming bacteria (Table 2). E. coli was found for septic procedures only. Streptococcus spp. were more common with aseptic procedures than with septic procedures (Table 2).
On the walls, colonies developed on only 60.7% (216/356) of the sedimentation plates. For both types of procedures (septic and aseptic) the most common pathogens were CNS (approximately 50%), followed by aerobic spore-forming bacteria (17% versus 33%), M. luteus (17% versus 10%), and molds (10% versus 7%). Streptococcus spp. were found for septic procedures only (6%). Because the power of the analysis was limited by the small amount of data, no significance calculation was performed. There was no microbial sedimentation of P. mirabilis, E. coli, E. faecalis, S. aureus, or P. stutzeri either at sampling locations S1 or S2 or on the procedure room walls.
This study found neither qualitative nor quantitative differences between the microbial load of procedure room air or microbial sedimentation for septic and aseptic procedures within general and visceral surgery. When interpreting the findings reported here it should be noted that the study was not originally planned as an equivalence or noninferiority study. The fact that the differences between the 2 procedure types were statistically insignificant cannot therefore be interpreted as direct evidence of equal microbial load. However, the consistency of the findings at the various stages of analysis does suggest that a noninferiority study planned to confirm these findings would yield comparable results. This is in line with the findings of Daschner et al. (22). Weist et al. (20) actually found a lower microbial load of procedure room air for septic procedures, though also with a higher proportion of typical nosocomial pathogens.
The mean microbial load of the air in the procedure room can be used as an indirect indicator of infection risk to the extent that the correlation between surgical wound infections and increased bacterial load in procedure room air following hip and knee replacement surgery is confirmed (23, 24).
The differences between surgery duration for the two procedure types can be explained by the fact that septic procedures were typically for the treatment of skin and soft tissue infections, whereas most aseptic procedures involved visceral surgery and thus longer procedures.
Microbial load of procedure room air is known to increase with the number of people present and the level of activity in the procedure room during surgery (25–27). Because the difference between the number of people present at the two procedure types was insignificant, it is unlikely that this parameter affected the microbial load of the procedure room air in this study. It is likely that activity levels were higher for orthopedic procedures, but the study findings do not indicate this. Finally, the increase in surgical wound infection rates in noisy conditions (28) and when non-surgery-related conversations are held (29) should be mentioned; this study did not examine these two issues.
As a limitation, it should be noted that only the mean microbial load of the procedure room air at 30-minute intervals was measured, not maximum peak loads. Weist et al. describe greater contamination of the area close to anesthesiologists and the space between sterile and nonsterile areas for septic procedures than for aseptic procedures (20). This study did not confirm these findings, either near to or further from the operating field.
As in the work by Friberg et al. (31), measurement of microbial sedimentation revealed a correlation between it and microbe levels in procedure room air. The greater release of Streptococcus spp. for aseptic procedures and of molds for septic procedures may be due to the fact that Streptococcus spp. are released from the oral cavity and respiratory tract and reach higher levels during aseptic procedures because these are on average substantially longer, while molds are probably agitated due to the higher level of activity of the surgical team. The fact that CNS and aerobic spore-forming bacteria are generally the most common pathogens is stated in multiple sources in the literature but is not microbiologically relevant to the procedures examined here (22, 32).
A potentially higher risk might be inferred only from the isolated occurrence of E. coli, E. faecalis, and P. mirabilis in septic procedures within 30 minutes of the end of surgery. However, even at a distance of 50 cm from the operating field only 2 CFU of E. coli were detected once, in only one septic procedure, and there was no sedimentation of P. mirabilis or E. faecalis near to the operating table.
The size of the sample does not allow a surgical wound infection rate to be inferred. Even if isolated pathogens remained in the air of the procedure room until the next procedure, which would only be possible in procedure rooms with no ventilation systems, levels would still fall far short of the threshold dose necessary to cause a surgical wound infection (Table 2, Table 3). For example, for transurethral application of P. mirabilis the threshold is 106 CFU (33); for surgical wound infections in animal experiments, the threshold for S. aureus is 103 to 107 CFU, for P. aeruginosa 103 to 105 CFU, and for B. fragilis and E. coli 105 to 108 CFU (34). Because modern surgical procedure rooms are fitted with ventilation systems with recovery times of no more than 20 minutes, after 30 minutes the aerogenic contamination risk for the next patient is very low. Where ventilation systems are present, the microbial load of the surroundings is quantitatively reduced by similar amounts for both septic and aseptic procedures, so no difference between the two is to be expected, but the risk of contamination is far lower than when there is no ventilation system.
Not establishing spatial separation between septic and aseptic procedures can be recommended without increasing the risk of infection, provided that basic hygiene measures are implemented, the surgical procedure room is not entered before the end of the stated induction period of surface disinfection, and the time interval between 2 procedures is sufficient (more than 30 minutes).
Our data does not indicate whether the conclusion that spatial separation between septic and aseptic procedures is unnecessary can be extrapolated to orthopedic/trauma surgery, particularly endoprosthetic implantation. However, as the literature provides no evidence that a lack of such separation is associated with an increased risk of infection, it can be presumed that if ventilation systems are of sufficient capacity a lack of separation does not increase the risk of infection.
This might not only lead to financial benefits for surgery departments as a result of better use of surgical capacities and lower construction-related investment costs but would also allow for more flexible planning in line with urgency of surgery rather than the required sequential order of septic and aseptic procedures. It is, of course, also possible to have a separate septic procedure room with entrance and exit points for reasons of capacity use, although this does not yield any additional benefit for patient safety.
Conflict of interest statement
Prof. Assadian has received consultancy fees from Mölnlycke Health Care, Hutchinson santé, and Ethicon. He has received reimbursement of travel costs and lecture fees from Ethicon.
Prof. Kramer has received reimbursement of travel costs and lecture fees from Ethicon.
The other authors declare that no conflict of interest exists.
Manuscript received on 25 November 2016, revised version accepted on
2 May 2017.
Translated from the original German by Caroline Shimakawa-Devitt, M.A.
Dr. med. Julian-Camill Harnoss
Department of General, Visceral and Transplantation Surgery
and Study Center of the German Surgical Society
University of Heidelberg
Im Neuenheimer Feld 110
69120 Heidelberg, Germany
air-conditioning systems in health-care settings—Guideline of the German Society for Hospital Hygiene (DGKH). GMS Hyg Infect Control 2016; 11: Doc03 MEDLINE PubMed Central
Division for Hospital Hygiene, Vienna General Hospital, Medical University Vienna: Prof. Dr. med. Assadian
Institute for Hygiene and Environmental Medicine, University of Greifswald: Dr. med. Müller, Dr. rer. med. Baguhl, Dr. med. Gessner, Prof. Dr. med. Kramer
Institute of Hospital Hygiene und Infection Prevention, Klinikum Konstanz: Prof. Dr. med. Dettenkofer
Institute for Community Medicine, University of Greifswald: Prof. Dr. phil. Kohlmann
Clinic and Outpatient Clinic for Surgery—Department of General Surgery, Visceral, Thoracic and Vascular Surgery, University of Greifswald: Prof. Dr. med. Heidecke
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