Operating-Room Airflow Technology and Infection Prevention

A handheld UV-C light-emitting diode decreases environmental contamination near the operative field

Introduction

Periprosthetic joint infection (PJI) may result from pathogen-to-patient transmission within the environment. High-touch surfaces (HTS) areas near the operative field from previous studies had been identified as the least likely to be thoroughly cleaned between operative cases and were utilized for this study. The purpose of this study was to assess the impact of a handheld ultraviolet-c (UV-C) light-emitting diode (LED) disinfection device on the decontamination of HTS in the operating room.

Methods

This prospective study was conducted between 03/02/2021 and 04/20/2021. Tryptic soy agar contact plates were used to determine the bacterial load of the selected surfaces before the initiation of the case, after the case was complete, before manual cleaning, and after disinfection of the LED device. The plates were then incubated for 48 hours at 36º +/-1° C. Colony forming units (CFU) were recorded 48 hours after incubation. Mean, median, and range of CFU were recorded.

Results

Average CFU per surface before and after the surgical case were 14.1 (range 0-200) and 13.5 (range 0-200) respectively, these were not significantly different (P = 0.9397). Manual cleaning reduced average CFU by 74% to 3.35 (range 0-200) per surface (P = 0.0162). Disinfection with the handheld LED unit further reduced the average CFU by 92% to 0.28 (range 0-4) per surface (P < 0.0001).

Conclusions

A handheld UV-C LED disinfection device may decrease environmental contamination near the operative field in HTS areas. Further research is warranted with this technology to determine if this correlates with a decrease in PJI.

Operating Room Air May Harbor Pathogens: The Role of an Ultraviolet Air Filtration Unit

BACKGROUND

One important factor for the prevention of surgical site infections is ultraclean air in the operating room (OR). Still, the direct sterilization potential of most technologies, especially in a dynamic clinical setting, is not well understood. We aimed to determine and compare the microbial presence from the inlet and outlet flow of a filtration unit with crystalline ultraviolet-C (C-UVC) light.

METHODS

A prospective study was conducted at a single institution, where primary total joint arthroplasty and spine surgeries were performed. The OR was fitted with a positive ventilation system. In addition, a filtration unit with a C-UVC sterilizing light was placed in the OR. The inlet and outlet air flows were swabbed simultaneously and compared. Swabs were processed for culture and next-generation sequencing.

RESULTS

The mean length of the surgical procedures sampled was 68 ± 13 minutes. Overall, 19 out of 200 (9.5%) swabs isolated microorganisms. Inlet air swabs were positive at a higher rate (16 versus 3%; P < .01) compared to the outlet air swabs. A wide variety of Gram-positive, Gram-negative, and anaerobic bacteria were isolated, but fungi were only recovered from inlet air swabs. The detection of microorganisms was also higher when more door openings were performed (32.5 ± 7.1 versus 27.9 ± 5.6; P < .01).

CONCLUSIONS

Air swabs mainly isolated microorganisms from the inlet flow to the filtration unit with a C-UVC light. The sterilizing unit counteracted factors affecting the air quality in the OR, namely door openings, surgical personnel, and tissue combustion.

Wearing a Surgical Vest With a Sterile Surgical Helmet System Decreases Contamination of the Surgical Field

BACKGROUND

Sterile surgical helmet systems are frequently utilized in total knee arthroplasty procedures to protect the surgeon while maintaining a comfortable working environment. However, common helmet systems pressurize the space between the surgical gown and the surgeon's skin. In gowns with a back seam, this may allow contaminated skin particles to escape into the surgical field. By measuring bacterial colony-forming units (CFUs), this study sought to determine if occlusion of the open back seam reduced the risk of potential contamination.

METHODS

First, qualitative analysis depicting airflow variations between gown configurations was performed using the Schlieren Spherical Mirror imaging system. Each gown configuration consisted of a sterile surgical helmet and one of 3 gown configurations: a standard gown with rear-tied closure, a standard gown with a surgical vest, and a zippered Toga-style gown. Next, a surgeon then performed simulated surgical activities for 60 minutes within a 1.4 m3 isolation chamber with work surfaces and controllable filtered air exchanges. During each procedure, contaminated particles were collected on sets of agar settle plates positioned directly behind the surgeon. Upon completion, the agar plates were incubated in a biolab, and the number of bacterial and fungal CFUs was counted. The experimental procedure was repeated 12 times for each gown configuration, with sterilization of the chamber between runs. Contamination rates were expressed as CFUs/m2/h.

RESULTS

The mean contamination rate measured with the standard gown was 331.7 ± 52.0 CFU/m2/h. After the addition of a surgical vest, this rate decreased by 45% to 182.2 ± 30.8 CFU/m2/h (P = .02). Similarly, with the Toga-style gown, contamination rates dropped by 49% to 170.5 ± 41.9 CFU/m2/h (P = .01).

CONCLUSIONS

When used in conjunction with surgical helmet systems, conventional surgical gowns do not prevent potential contamination of the surgical field. We recommend that staff within the surgical field cover the back seam of standard gowns with a vest or don a zippered Toga-style gown.

Implementation of an adapted perioperative ventriculoperitoneal shunting protocol in a tertiary center located in a low-to-middle-income country

OBJECTIVE

Preventative protocols have efficaciously reduced shunt infection in developed countries. However, the generalizability of these protocols in low-to-middle-income countries (LMICs) remains unclear. Previously, shunt insertion in the authors' center was routinely performed under institutional preventative precautions, which was updated via merging with the Hydrocephalus Clinical Research Network (HCRN) protocol. This study aimed to investigate the ventriculoperitoneal shunt (VPS) infection rates in pediatric patients following the implementation of the adapted protocol.

METHODS

The adapted protocol was implemented in all first-time VPS implantations between 2011 and 2021. The primary outcome was a 6-month shunt infection. The Pearson chi-square test was used for categorical variables and the Mann-Whitney U-test for numeric variables to evaluate the correlation with shunt infection.

RESULTS

A total of 352 first-time VPS procedures were performed adhering to the adapted protocol. The median age was 5 months, and 189 (53.7%) were male. Overall, 37 patients (10.5%) experienced shunt infection, with 30 (8.5%) occurring within the first 6 months, which was lower than 13.3% infection rate of the previous series of the same center. The infection rate was slightly higher than the 5.7% and 6.0% rates reported by HCRN studies. Patients with shunt infection were significantly younger (7.5 versus 17.5 months, P < 0.001).

CONCLUSIONS

This study validates the efficacy of an adapted perioperative protocol in mitigating shunt infection in a high-volume center in a LMIC. Adhering to a step-by-step protocol, modified to suit the healthcare resources and financial constraints of LMICs, could maintain low shunt infection rates that are roughly comparable to those of centers in high-income countries.

Impact of a Task-Grabbing System for surgical technicians on operating room efficiency

The purpose of this study was to evaluate the effect of the Task-Grabbing System on operating room efficiency. Based on the competition-driven concept of the 'Uber' app, an Task-Grabbing System was designed for task allocation and quality assessment. We implemented the Task-Grabbing System in our hospital operating room and compared the differences in consecutive operation preparation time, turnover time, and task completion time performed by surgical technicians for tasks such as patient pick-up, operating room cleaning, medical equipment recovery, three-piece set delivery, as well as blood gas analysis and intraoperative specimen submission before (October 2019) and after (December 2019) the implementation of the Task-Grabbing System. After the implementation of the Task-Grabbing System, the consecutive operation preparation time was reduced from the average of 43.56-38.55 min (P < 0.05), and the turnover time was decreased from the average of 14.25-12.61 min (P < 0.05). And the respective time consuming of surgical technicians for patients picking up, operating room cleaning, medical facilities recovering, the three-piece set delivering, blood gas analysis sending and intraoperative specimen submitting was significantly shortened (P < 0.05). The Task-Grabbing System could improve the operating room efficiency and effectively mobilize the enthusiasm and initiative of the surgical technicians.

Sterile Setup Table in the Operating Room Is Not So Sterile

BACKGROUND

One of the important factors for surgical site infection prevention is the implementation of an ultraclean operating room. This study was designed to evaluate back-table sterility during total joint arthroplasty.

METHODS

This prospective study includes 52 patients undergoing primary total joint arthroplasty between November 2021 and January 2022. A total of 4 swabs (2 air swabs and 2 table swabs) were obtained for each case, at the conclusion of surgery and prior to the takedown of drapes. One swab from each set was sent for culture, and the other was sent for next-generation sequencing (NGS) analysis.

RESULTS

Among 104 back-table swabs, a total of 13 (12.5%) organisms were isolated. Of these, 7 organisms were isolated by culture and 6 by NGS. No microorganisms were isolated by both culture and NGS from back-table swabs. Among 104 air swabs, a total of 11 (10.6%) organisms were isolated. Of these, 6 microorganisms were isolated by culture and 5 by NGS. In 4 of the 104 swabs, both culture- and NGS-isolated organisms were from air swabs. Of the 104 (12.5%) back-table and air swabs, 13 were culture positive. While more than 1 pathogen was identified in 2 air swabs, all back-table swabs were monomicrobial by culture. Pathogens were identified from 11 of 104 (10.6%) swabs by NGS, while more than 1 pathogen was identified in 4 swabs (2 air and 2 back table).

CONCLUSION

The findings of this study raise an important issue that the surgical field including the sterile table setup for instruments is not "sterile" and can harbor pathogens.

Role of Operating Room Size on Air Quality in Primary Total Hip Arthroplasty

BACKGROUND

Airborne biologic particles (ABPs) can be measured intraoperatively to evaluate operating room (OR) sterility. Our study examines the role of OR size on air quality and ABP count in primary total hip arthroplasty (THA).

METHODS

We analyzed primary THA procedures done within 2 ORs measuring 278 ft² and 501 ft² at a single academic institution from April 2019 to June 2020. Temperature, humidity, and ABP count per minute were recorded with a particle counter intraoperatively and cross-referenced with surgical data from the electronic health records using procedure start and end times. Descriptive statistics were used to evaluate differences in variables. P-values were calculated using t-test and chi-squared test.

RESULTS

A total of 116 primary THA cases were included: 18 (15.5%) in the "small" OR and 98 (84.5%) in the "large" OR. Between-group comparisons revealed significant differences in temperature (small OR: 20.3 ± 1.23 C versus large OR: 19.1 ± 0.85 C, P < .0001) and relative humidity (small OR: 41.1 ± 7.24 versus large OR: 46.9 ± 7.56, P < .001). Significant percent decreases in ABP rates for particles measuring 2.5 um (-125.0%, P = .0032), 5.0 um (-245.0%, P = .00078), and 10.0 um (-413.9%, P = .0021) were found in the large OR. Average time spent in the OR was significantly longer in the large OR (174 ± 33 minutes) compared to the small OR (151 ± 14 minutes) (P = .00083).

CONCLUSION

Temperature and humidity differences and significantly lower ABP counts were found in the large compared to the small OR despite longer average time spent in the large OR, suggesting the filtration system encounters less particle burden in larger rooms. Further research is needed to determine the impact this may have on infection rates.

Effectiveness of Manual Terminal Cleaning Varies on High-Touch Surfaces Near the Operative Field

Background

Periprosthetic joint infection may result from pathogen to patient transmission within the environment. The purpose of this study is to evaluate the contamination level of selected high-touch surfaces in the operating room (OR) using a blacklight fluorescent marking system after a manual terminal clean.

Methods

Prior to the manual terminal clean, 16 high-touch surfaces were marked using a blacklight fluorescent gel. The marked areas were assessed the next morning for thoroughness of cleaning. Surfaces were categorized based on the average percent of the marks removed as “clean” (>75%), “partially clean” (26%-74%), or poorly cleaned (<25%). This process was repeated randomly 12 times. Terminal cleaning was done in the standard fashion, and the perioperative team was unaware of the initiation of this study.

Results

A total of 936 marks were analyzed. There was a significant difference in the number of marks completely clean (29.1%, 272/936) vs marks that were not touched (40.8%, 382/936), P < .001. Only the OR back table (75%) had a rating of clean. Partially clean areas included Mayfield table (72%), overhead lights (70.1%), infusion pump (61.1%), clock reset button (58.3%), table remote control (50%), tourniquet machine (50%), and the OR table (33.3%). Poorly cleaned surfaces included anesthesia medication cart (21.8%), door handles (20.8%), phone (16.7%), electrocautery unit (16.7%), foot pedal (16.7%), anesthesia cart (16.2%), nurses’ station (14.1%), and supply cabinet doors (6%).

Conclusions

Effectiveness of manual terminal cleaning varied greatly across surfaces. In general, surfaces further from the operative field were less likely to have markings removed.

Are Operating Rooms With Laminar Airflow a Risk for Inadvertent Perioperative Hypothermia During Ureterorenoscopic Lithotripsy Under Spinal Anesthesia? A Prospective Randomized Clinical Trial

OBJECTIVES

Inadvertent perioperative hypothermia (IPH), defined as a core temperature <36°C, is common during a surgical procedure and is associated with high morbidity and mortality. Laminar (LAS) and conventional airflow systems (CAS) are used frequently for clean microenvironmental surgical areas in operating rooms. In LAS, the cold airflow is directed toward the patient, unlike CAS. Does this airflow in LAS cause heat loss from the patient by convection more than CAS? We aimed to compare the IPH frequencies of these airflow systems on patients who underwent ureterorenoscopic lithotripsy (ureterorenoscopic surgery) under spinal anesthesia.

METHODS

The study was a prospective, parallel-group, randomized trial. A total of 246 volunteers were included in the study and divided into group LAS (n = 123) and group CAS (n = 123). Randomization of patients was performed using the closed-envelope method (as 1:1).The tympanic membrane temperature of patients was measured before spinal anesthesia ( T0 ) and then every 15 minutes ( T n ) during the procedure. The IPH ratio and the change of the tympanic temperatures (Δ T ) were recorded (clinical trial number: IRCT20180324039145N5).

RESULTS

In total, there were no statistical differences between the IPH ratios of group LAS and group CAS (61.2% [71 of 116] versus 49.6% [57 of 115], respectively; P = 0.075). The IPH ratio was 55.4% (128 of 231). The tympanic temperatures of patients decreased about 0.64°C (0.45°C) at the 30th minute. In both groups, Δ 30 was similar (0.62; 95% confidence interval, 0.52-0.72 [ P = 0.65]; 95% confidence interval, 0.55-0.74 [ P = 0.236], respectively).

CONCLUSIONS

The risk for IPH of both LAS and CAS in the operating room is similar during ureterorenoscopic surgery.

Comparison of Operating Room Air Quality in Primary Versus Revision Total Knee Arthroplasty

BACKGROUND

Airborne biologic particles (ABPs) can be measured intraoperatively to evaluate operating room (OR) sterility. Particulate matter (PM) up to 2.5 microns can contain microbial species which may increase infection risk. Our study examines the differences in air quality and ABP count in primary total knee arthroplasty (TKA) and revision TKA (rTKA).

METHODS

We analyzed primary and rTKAs in a single OR at an academic institution from January 2020 to December 2020. Procedures from March 15, 2020, to May 4, 2020, were excluded to avoid COVID-related confounding. Temperature, humidity, and ABP count per minute were recorded with a particle counter intraoperatively and cross-referenced with surgical data from the electronic health records using procedure start and end times. Descriptive statistics were used to evaluate the differences in variables. P values were calculated using t-test and chi-square test.

RESULTS

A total of 107 TKA cases were included: 79 (73.8%) primary TKAs and 28 (26.2%) rTKAs. Time spent in an OR was significantly higher for rTKAs (primary: 176 ± 46.7 minutes vs revision: 220 ± 47.1 minutes, P < .0001). Compared to primary TKAs, rTKAs had significant percent increases in ABP rates for particles measuring 0.3 μm (+70.4%, P < .001), 0.5 μm (+97.2%, P < .0001), 1.0 μm (+53.2%, P = .001), and 2.5 μm (+30.3%, P = .017) and for PM 2.5 (+108.3%, P < .001) and PM 5.0 (+105.6%, P < .001).

CONCLUSION

rTKAs had significantly longer time spent in an OR and significant percent increases in ABP rates for particles measuring 0.3 μm, 0.5 μm, and 1.0 μm compared to primary TKAs. Measurements of PM 2.5 and 5.0 (which can contain large numbers of microbes) were also significantly greater in rTKAs. Further research is needed to determine whether the size and quantity of ABPs translate to higher infection rates after rTKA.

A back table ultraviolet light decreases environmental contamination during operative cases

BACKGROUND

The purpose of this study is to assess the impact of a germicidal ultraviolet light-emitting diode (LED) on the contamination level of a back table in the operating room (OR) during total joint arthroplasty procedures.

METHODS

Eight Tryptic Soy Agar petri plates were placed on a table located near the operative field and exposed to air. One plate was removed on the hour over an 8-hour time span. The back table had either an UV-LED for disinfection or a sham UV-LED. This process was repeated in 12 different ORs (6 with UV light, 6 with sham device). The plates were then incubated for 48 hours at 36°C ± 1°C . Colony forming units (CFU) were recorded 24 and 48 hours after incubation.

RESULTS

There was a statistically significant difference in total CFUs between the intervention vs sham at 24-hours (27 vs 95, P = .0001) and 48-hours (38 vs 122, P < .0001). The multivariate analysis revealed that the 24-hour and 48-hour count, the predictors UV light (P = .002) and hour of plate removal (P = .050) were statistically significantly associated with CFU counts. Together, the predictor variables explained 15.8% and 23.0% of the variance in CFU counts at 24- and 48-hours, respectively.

CONCLUSIONS

A back table UV-LED may decrease environmental contamination near the operative field. This has potential to lead to a decrease in joint infection.

Does the Laminar Airflow System Affect the Development of Perioperative Hypothermia? A Randomized Clinical Trial

OBJECTIVES

We aimed to compare tympanic membrane temperature changes and the incidence of inadvertent perioperative hypothermia (IPH) in patients undergoing laparoscopic cholecystectomy under general anesthesia in laminar airflow systems (LAS-OR) and conventional turbulent airflow systems (CAS-OR).

BACKGROUND

Different heating, ventilation, and air-conditioning (HVAC) systems are used in the operating room (OR), such as LAS and CAS. Laminar airflow is directed directly to the patient in LAS-OR. Does laminar airflow in ORs cause faster heat loss by convection?

METHODS

This is a prospective, randomized study. We divided 200 patients with simple randomization (1:1), as group LAS and group CAS, and took the patients into the LAS-OR or CAS-OR for the operation. Clinical trial number: IRCT20180324039145N3. The tympanic membrane temperatures of patients were measured (°C) before anesthesia induction (T ₀) and then every 15 min during surgery (T_n). Changes (Δ_n) between T ₀ and T_n were measured.

RESULTS

In the first 30 min, there was a temperature decrease of approximately 0.8 °C (1.44 °F) in both groups. Temperature decreases at 45 min were higher in group LAS than in group CAS but not statistically significant, Δ₄₅, respectively, 0.89 (95% confidence interval [CI] [0.77, 1.02]) versus 0.77 (95% CI [0.69, 0.84]; p = .09). IPH occurred in a total of 60.9% (112 of 184) of patients in the entire surgical evaluation period in group LAS and group CAS (58.9% vs. 62.8%, p = . 59).

CONCLUSIONS

IPH is seen frequently in both HVAC systems. Clinically, the advantage of HVAC systems relative to each other has not been demonstrated during laparoscopic cholecystectomy.

Higher Surgery and Recovery Room Air Pressures Associated with Reduced Surgical Site Infection Risk

BACKGROUND

Incisional surgical site infections (SSIs) following coronary artery bypass grafting (CABG) prolong hospital stays, elevate healthcare costs and increase likelihood of further complications. High air pressure deactivates bacteria and is utilized for commercial food preservation, assuring microbiologically safe pharmaceuticals and sanitizing instruments. However, research on utilizing air pressure deactivation thresholds in surgical and postoperative rooms to reduce rates of SSIs is lacking.

METHODS

A case-control study of 801 CABG patients, 128 SSI cases and 673 controls was conducted from January 1, 2006 through March 31, 2009 in Yerevan, Armenia. Patient and surgery characteristics, air pressure measurements and seasons were selected as independent variables with SSI rates as the outcome. The novel threshold regression analysis was used to determine potential air pressure bacterial deactivation thresholds. A final multivariate logistic regression model adjusted for confounders.

RESULTS

Overall, bacterial deactivation air pressure threshold was 694.2 mmHg, with the presence of infection for higher air pressure values not statistically significant from zero. Individual deactivation thresholds for Staphylococcus epidermidis (threshold = 694.2 mmHg) and Escherichia coli (threshold = 689.2) showed similar patterns. Multivariate logistic regression showed air pressure above the deactivation threshold was highly protective against SSIs with adjOR = 0.27 (p-value = 0.009, 95%CI: 0.10-0.72). Other SSI risk factors included female sex, adjOR = 2.12 (p-value = 0.006, 95%CI: 1.24-3.62), diabetes, adjOR = 2.61 (p-value < 0.001, 95%CI: 1.72-3.96) and longer time on ventilator, adjOdds = 1.01 (p-value = 0.012, 95%CI: 1.00-1.02).

CONCLUSION

Maintaining air pressures in operating and postoperative rooms exceeding bacterial-deactivation thresholds might substantially reduce SSI rates following surgery. Further research should identify specific bacterial-deactivation air pressure thresholds in surgical and postoperative rooms to reduce SSI rates, especially for drug-resistant bacteria.

The Implementation of a Complication Avoidance Care Bundle Significantly Reduces Adverse Surgical Outcomes in Orthopedic Trauma Patients

Background: Surgical complications are associated with a significant burden to patients and hospitals and are increasingly discussed in recent literature. This cohort study reviewed surgery-related complications in a Level I trauma center. The effect of a complication avoidance care bundle on the rate of surgical complications was analyzed. Methods: All complications (surgical and nonsurgical) that occur in our trauma department are prospectively captured using a standardized documentation form and are discussed and analyzed in a weekly trauma Morbidity and Mortality (M&M) conference. Surgical complication rates are calculated using the annual surgical procedure numbers. Based on discussions in the M&M conference, a complication avoidance care bundle consisting of five measures was established: (1) Improving team situational awareness; (2) reducing operating room traffic by staff members and limiting door-opening events; (3) preoperative screening for infectious foci; (4) adapted preoperative antibiotic prophylaxis in anatomic regions with a high risk of infectious complications; and (5) use of iodine-impregnated adhesive drape. Results: The number of surgical procedures steadily increased over the study years, from 3587 in 2015 to 3962 in 2019 (an increase of 10.5%). Within this 5-year study period, the overall rate of surgical complications was 0.8%. Surgical site infections were the most frequently found complications (n = 40, 24.8% of all surgical complications), followed by screw malposition (n = 20, 12.4%), postoperative dislocations of arthroplasties (n = 18, 11.2%), and suboptimal fracture reduction (n = 18, 11.2%). Following implementation of the complication avoidance care bundle, the overall rate of surgical complications significantly decreased, from 1.14% in the year 2016 to 0.56% in the study year 2019, which represents a reduction of 51% within a 3-year time period. Conclusions: A multimodal strategy targeted at reducing the surgical complication rate can be successfully established based on a transparent discussion of adverse surgical outcomes. The combination of the different preventive measures was associated with reducing the overall complication rate by half within a 3-year time period.

A Clinical Test to Measure Airborne Microbial Contamination on the Sterile Field During Total Joint Replacement: Method, Reference Values, and Pilot Study

Background

Airborne microbe-carrying particles in the operating-room environment during total joint replacement are a risk factor for periprosthetic joint infection. The present study focuses on a simple environmental test, based on practices used in aseptic cleanrooms, to quantify the deposition of microbe-carrying particles onto the sterile field.

Methods

Settle plates are exposed Petri dishes. A settle plate test system and sampling plan were developed from current practices used in aseptic manufacturing. A pilot study evaluated this system in an orthopaedic operating room during 22 total knee and hip arthroplasties. The microbial deposition total (MDT), expressed in colonies/m², is proposed as an outcome variable to report airborne sterile-field contamination as measured with settle plates. Two reference MDT levels were developed: (1) an upper limit of 450, corresponding with the ultraclean air definition of 10 colonies/m³, and (2) a target level of 100, corresponding with 1 colony/m³. These levels also correspond with widely used limits in aseptic cleanrooms and controlled environments.

Results

High MDT standard deviations were noted. Ninety-one percent (95% confidence interval, 71.0% to 98.7%) of wound zone MDT levels were within the upper limit. Twenty-seven percent (95% confidence interval, 12.9% to 48.4%) of wound zone levels were within the target level.

Conclusions

Settle plates are a feasible technique to test environmental levels of microbe-carrying particles on sterile fields during total joint replacement for scientific and environmental quality studies.

Clinical Relevance

This settle plate operating-room environmental test can be used in future research to validate the presence of actual ultraclean-air conditions during periprosthetic joint infection outcome studies. Surgeons also can use this test to measure intraoperative airborne microbe-carrying-particle sterile-field contamination and compare it with ultraclean-air reference levels for environmental quality-control programs.