Bacterial Contamination of Lead Aprons in a High-Volume Cardiac Catheterization Laboratory and Disinfection Using an Automated Ultraviolet-C Radiation System

Abstract: Objectives. Quantify and characterize bacterial contamination of lead aprons in a high-volume catheterization laboratory and evaluate the efficacy of decontamination using an ultraviolet-C (UV-C) radiation system. Background. Bacterial contamination and ineffective disinfection of personal protective equipment in medical centers pose potential health risks to patients and medical staff. The contamination burden of lead aprons and a reliable disinfection strategy are unknown. Methods. Ten routinely used, unsterilized lead aprons from a high-volume catheterization laboratory were studied. Standard and bacteria-resistant outer fabrics were included. Swabbings from four locations on each apron (inner thyroid collar, chest, waist, and bottom border) were obtained at baseline and after a 15-minute decontamination cycle using the UV-C based DCab System (Nosocom Solutions). Colony counts, speciation, and antibiotic resistance were obtained from aerobic and anaerobic cultures. Results. Baseline cultures grew ≥1 colony from 25 of 40 samples (62.5%; 310 colonies; 0-100 colonies/sample; 16 organisms), mainly skin and mouth flora without antibiotic resistance. Baseline growth was greatest from the thyroid collar and similar between different fabrics. UV-C reduced subsequent growth (7.8 ± 23.8 colonies overall vs 0.1 ± 0.3 colonies overall; P<.001), with all four isolates considered contaminants of laboratory handling. Colony counts were reduced in thyroid collar, chest, waist, nylon fabric, polyurethane fabric, and alternative bacteria-resistant fabric subgroups (all P<.05). Conclusions. Routinely used lead aprons in a high-volume catheterization laboratory were contaminated by non-pathogenic skin and mouth flora located predominantly on the thyroid collar. Disinfection using an automated UV-C based system is highly effective across different apron surface locations and fabric types. 

J INVASIVE CARDIOL 2018;30(11):416-420.

Key words: bacterial contamination, cardiac catheterization laboratory, DCab device decontamination, disinfection, health-care associated infection, lead apron, personal protective equipment, ultraviolet-C

Health-care associated infection (HAI) is a major concern of modern health-care providers due to increased risk of patient adverse events and increased cost.^1-3 Significant efforts to prevent HAI and reduce its health-care impact have been made,^4,5 with particular attention paid to modes of infection transmission, including hand hygiene, central-line associated blood-stream infections, catheter-associated urinary tract infections, ventilator-associated pneumonia, surgical-site infections, and multidrug-resistant organisms.⁶ 

Personal protective equipment (PPE) and hospital staff attire have both been shown to harbor bacterial contaminants.^7-12 However, while sterile procedural technique and disinfection of hospital environmental surfaces are routinely enforced, the role of contaminated PPE and staff attire in nosocomial infections remain poorly understood and inconsistently addressed. In particular, contamination and ineffective disinfection of lead aprons and thyroid collars may expose both patients and health-care workers to increased risk of nosocomial infections. This study investigated the burden of bacterial contamination of routinely used lead aprons and the efficacy of automated PPE disinfection using an ultraviolet-C (UV-C) radiation device in a high-volume catheterization laboratory.

Methods

The study protocol was designed by the investigators (LA and EM) and approved by the University of California, San Diego Institutional Review Board. Ten different lead aprons were tested for bacterial contamination before and after automated disinfection using the UV-C radiation DCab system (Nosocom Solutions) (Figure 1). Aprons of various construction, covered with standard nylon fabric (4 aprons; Bar-Ray Products), bacteria-resistant polyurethane (3 aprons; Bar-Ray Products), or a bacteria-resistant alternative (3 aprons; Infab Corporation) were obtained from the cardiac catheterization laboratory of a high-volume academic medical center. Each apron was used on a regular basis for at least 12 consecutive months by a single operator and never previously disinfected. 

Bacterial sampling of each apron was performed in a standardized fashion before and after UV-C treatment. During each sampling procedure, a single liquid-based multipurpose swab (ESwab; Copan Diagnostics) was dipped in sterile liquid medium, rubbed vigorously within a 2 inch x 2 inch area, then housed in a collection tube for transport to the clinical microbiology laboratory. There was no overlap of swabbed areas. Four different locations on each lead apron were sampled, including: (1) the inner (skin-facing) surface of the thyroid collar; (2) chest; (3) waist; and (4) bottom border (Figure 2).

Apron disinfection using the DCab system is fully automated. Within its chamber are five different positions for hanging aprons/garments on specialized racks. Both sides of each hanging apron are automatically scanned by robotic arms housing UV-C lamps over a 15-minute decontamination cycle. Afterward, outer indicator lights signal when a cycle is complete. DCab users are shielded from UV-C exposure by light-filtering windows and chamber doors that need to be fully closed before use. In this study, disinfection was performed by hanging a lead vest and a lead skirt in the second and fourth positions, respectively, for a 15-minute decontamination cycle. Thyroid collars were separated from lead vests, attached to the hanging racks, and decontaminated together in a single cycle.

Bacterial swabs were randomly numbered, delivered to the clinical microbiology laboratory at room temperature, and processed per standard clinical protocol within 4 hours from collection. Each ESwab was processed automatically by a robotic specimen processor (Walk-Away Specimen Processor; Copan Diagnostics) using 10 µL of liquid medium per laboratory protocol. Specimens were cultured on plates of sheep blood, colostin nalodexic acid agar, MacConkey agar, and chocolate agar for aerobic organisms. Anaerobic organisms were cultured on Brucella agar (all plates from Thermo Fisher Scientific). Aerobic plates were observed >48 hours and anaerobic plates were observed >7 days for growth. Organism identification was usually achieved within 24-48 hours. Subsequent antibiotic susceptibility was performed using the Phoenix automated test (BD) or ETEST manual test (bioMérieux). The results of bacillus and diptheroid species were not able to be further classified. Results were processed by clinical laboratory personnel, then transmitted to the research team once finalized. Presence of contaminants due to sample processing and handling were independently adjudicated by the clinical laboratory as part of standard-of-care. Laboratory technologists were blinded during the course of the study. Pathogenic species were defined as methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus, extended-spectrum beta-lactamase-producing Enterobacteriaceae, and Clostridium difficile.

Statistical analysis. Wilcoxon signed-rank testing was used to compare matched colony counts resulting from bacterial sampling before vs after UV-C disinfection. Secondary analyses of baseline bacterial contamination and UV-C treatment efficacy were repeated across different sampling locations and fabric types. Student’s t-test, analysis of variance (ANOVA), and Brown-Forsythe analyses were used to compare predisinfection and postdisinfection results among subgroups. Results were reported as means ± standard deviations. Significant relationships were defined as having P-value <.05.

Results

Final cultures demonstrated bacterial growth from 29 out of 80 total samples (36.3%; 314 total colonies; range, 0-109 colonies/sample). Bacterial growth resulted from 25 out of 40 predisinfection samples (62.5%; 310 colonies; range, 0-109 colonies/sample), while single bacterial colonies grew from 4 out of 40 postdisinfection samples (10.0%; 4 colonies; 1 colony/sample) (Table 1). All postdisinfection colonies were determined to be laboratory contaminants by a blinded clinical microbiologist. The thyroid collar was the source location of most bacterial growth (9 out of 10 samples; 278 colonies; range, 0-109 colonies/sample), followed by chest (7 out of 10 samples; 15 colonies; range, 0-4 colonies/sample), waist (7 out of 10 samples; 12 colonies; range, 0-5 colonies/sample), and bottom border (2 out of 10 samples; 5 colonies; range, 0-3 colonies/sample) (ANOVA, Brown-Forsythe, and post hoc P<.05). Baseline colony counts were also similar between nylon vs bacteria-resistant fabrics (9.3 ± 27.1 colonies vs 6.7 ± 21.9 colonies; P=.74).

A total of 16 different organisms were grown (Table 2); the majority were known to be normal skin and mouth flora. Propionibacterium acne yielded the greatest number of colonies (269 colonies) followed by coagulase-negative Staphylococcus (30 colonies). Postdisinfection contaminants included three separate colonies of Staphylococcus epidermidis and one colony of Propionibacterium acne. No epidemiologically important antibiotic-resistant pathogen, including methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus, extended-spectrum beta-lactamase-producing Enterobacteriaceae, and Clostridium difficile, was grown from study samples. Furthermore, no antibacteria-resistant organism was identified.

Initial analyses were performed including bacterial contaminants in the postdisinfection results. Overall colony counts were significantly lower following decontamination (7.8 ± 23.8 colonies vs 0.1 ± 0.3 colonies; P<.001). Colony counts were also reduced in thyroid collar (27.8 ± 43.0 colonies vs 0.2 ± 0.4 colonies; P=.01), chest (1.5 ± 1.4 colonies vs 0.1 ± 0.3 colonies; P=.03), waist (1.2 ± 1.5 colonies vs 0 colonies; P=.01), nylon fabric (9.3 ± 27.1 colonies vs 0.3 ± 0.4 colonies; P<.01), polyurethane fabric (3.9 ± 10.8 colonies vs 0 colonies; P=.02), and alternative bacteria-resistant fabric subgroups (9.5 ± 29.5 colonies vs 0 colonies; P=.02) (Figure 3). Postdisinfection growth was similar between thyroid collar vs other sampling locations (0.2 ± 04 colonies vs 0.1 ± 0.3 colonies; P=.36), but greater on nylon vs bacteria-resistant fabrics (0.3 ± 0.4 colonies vs 0.0 ± 0.0 colonies; P=.04).

When accounting for contaminants of laboratory processing, there was no abnormal bacterial growth among postdisinfection samples. UV-C treatment resulted in significantly reduced colony counts overall (P<.001), as well as in thyroid collar (P<.01), chest (P=.02), waist (P=.01), nylon fabric (P<.01), polyurethane fabric (P=.02), and alternative bacteria-resistant fabric subgroups (P=.02). No significant change in colony counts was detected in the bottom border location when including (0.5 ± 1.1 colonies vs 0.1 ± 0.3 colonies; P=.28) or excluding laboratory contamination results (P=.18).

Discussion

Results of this study demonstrate that routinely used lead aprons in a high-volume cardiac catheterization laboratory: (1) are predominantly contaminated by normal skin and mouth bacterial flora; (2) are more heavily contaminated along the inner surface of the thyroid collar; (3) are effectively disinfected by UV-C treatment using the automated DCab system; and (4) are effectively disinfected across different apron locations and fabric types.

Mainstream efforts to study and manage HAI have not focused on disinfection of PPE, including lead aprons. Few studies on the subject have shown variable results, ranging from rare detection of normal skin flora^9,10 to frequent identification of bacteria including potentially pathogenic species.^7,11,12 Our findings show frequent detection of normal skin flora in pretreatment samples and absence of pathogenic species. The absence of pathogenic species in this study was unexpected because the test aprons were used regularly for 12 months prior to testing and never previously sanitized. However, it is possible that these pathogens are absent due to controlled access to the catheterization laboratory, sterile operator technique, and routine room disinfection following treatment of patients with known pathogens.

Frequent isolate growth and high colony counts from thyroid collar baseline samples were consistent with other studies that have produced similar results.^10-12 Speciation and antibiotic resistance from thyroid collar isolates were of particular interest in this study because the collar is positioned in direct contact with skin and serves as a plausible mechanism by which HAI is spread. However, in the absence of pathogenic study sample isolates, the current study does not validate theories that HAI is caused by pathogenic contamination of thyroid collars and propagated by the sharing of collars among health-care workers.

Disinfection of aprons using UV-C treatment was highly effective in this study. While the efficacy of UV-C is well established in other applications, the DCab system to our knowledge is the only commercially available device designed to automatically disinfect health-care PPE using UV-C. Posttreatment results essentially showed little or no significant bacterial growth following exposure to UV-C. The preprogrammed 15-minute disinfection cycle was sufficient time to achieve complete inhibition of subsequent bacterial growth. Automated scanning of the UV-C source within the disinfection chamber also facilitated broad inhibition of bacterial growth from the entire apron.

Special bacteria-resistant fabrics marketed by apron manufacturers are routinely used in the cardiac catheterization laboratory and included in this study. However, study findings revealed similar levels of baseline bacterial contamination from standard vs antimicrobial fabrics. Furthermore, UV-C treatment achieved complete disinfection regardless of fabric type. While the current study failed to demonstrate an advantage to using an antimicrobial fabric, it is possible that these materials have a limited duration of efficacy or facilitate disinfection by other means (eg, wiping or spraying chemical sanitizers onto apron surfaces).

Study limitations. It is possible that pathogenic isolates were not found due to testing of relatively “new” aprons (manufactured between 1-4 years before testing), which were used by individual (rather than multiple) operators. Study aprons were selected for their high frequency of use, similar fabrication dates, and utilization of various bacteria-resistant fabrics. It is also possible that pathogenic organisms were indeed present, but not detected, due to the limited number of study samples. This study also did not investigate disinfection efficacy in the following manners: (1) using different UV-C exposure times; (2) on apron surfaces not directly exposed to UV-C within the DCab chamber (eg, flaps, outer sides, inner vest, or skirt surfaces); or (3) against viral and fungal contaminants. 

Conclusion

Routinely used lead aprons in a high-volume cardiac catheterization laboratory are contaminated by non-pathogenic skin and mouth bacterial flora located predominantly on the inner thyroid collar surface. Automated disinfection using the UV-C radiation DCab system is highly effective across different apron surface locations and outer fabric types.

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From the University of California, San Diego Sulpizio Cardiovascular Center, La Jolla, California.

Funding: This study was supported by a research grant from Nosocom Solutions, Inc. Terms of this arrangement have been reviewed and approved by the University of California, San Diego in accordance with its conflict of interest policies.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.

Manuscript submitted July 4, 2018, provisional acceptance given July 12, 2018, final version accepted July 25, 2018.

Address for correspondence: Ehtisham Mahmud, MD, FACC, FSCAI, Professor of Medicine/Cardiology Chief of Cardiovascular Medicine, UC San Diego Sulpizio Cardiovascular Center, 9434 Medical Center Drive #7844, La Jolla, CA 92037. Email: emahmud@ucsd.edu