Date of Award

12-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Food Technology

Committee Chair/Advisor

Xiuping Jiang

Committee Member

Angela Fraser

Committee Member

E Jeffery Rhodehamel

Committee Member

Charles Pettigrew

Committee Member

David Buckley

Abstract

Long-term care facilities (LTCFs) provide an environment favorable for the transmission of three critical human pathogens: human norovirus (HuNoV), severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and Clostridioides difficile. Given residents in LTCFs are susceptible to infections due to their advanced ages and compromised immune systems, effective environmental surface disinfection plays a crucial role in controlling the spread of human pathogens within these settings and, therefore, mitigates the risk of infections caused by these pathogens. This dissertation aimed to assess the efficacy of various types of disinfectants against two HuNoV surrogates [feline calicivirus (FCV) and Tulane virus (TuV)], two SARS-CoV-2 surrogates [bovine coronavirus (BCoV) and human coronavirus (HCoV) OC43], and C. difficile endospores. The research encompasses surfaces commonly encountered in healthcare settings and public spaces, with a particular emphasis on the disinfection of these pathogens on soft porous surfaces in LTCFs.

First, nine chemical disinfectants on EPA’s List G were selected using four criteria: 1) ready-to-use, 2) nonchlorine-based active ingredient, 3) commercially available, and 4) limited known health risks. Active ingredients of the products included hydrogen peroxide (H2O2), peracetic acid, quaternary ammonium compounds, or alcohols. The efficacy of the products against FCV, TuV and C. difficile spores was first screened using the American Society for Testing and Materials (ASTM) suspension test, and then the carrier test on stainless steel coupons for 1, 5 and 10 min (FCV, TuV) and 10 min (C. difficile spores). On stainless steel carriers, 8 of 9 products could reduce >3 log10 PFU of FCV within 5 min. One most efficacious product containing H2O2 as key active ingredient, reduced >5.1 log10 PFU of FCV and >3.1 log10 TCID50 of TuV after 5 min, and >6.0 log10 CFU of C. difficile endospores after 10 min. Of the five products containing H2O2,no strong correlation (R2=0.25, p=0.03) was observed between disinfection efficacy and H2O2 concentration. The addition of 0.025% ferrous sulfate to 1% H2O2 solution improved efficacy against all FCV, TuV, and C. difficile. Our results confirmed that both product formulation and the active ingredient concentration influence the efficacy. Additionally, TuV proved to be a more conservative surrogate for HuNoV than FCV.

Next, this dissertation evaluated the efficacy of chemical disinfectants (products A, B, and C) and steam vapor against HuNoV on nylon carpet with two different backings. Carpet coupons (5×5 cm2) inoculated with a mixture of FCV and TuV were allowed to dry at room temperature under 30-50% relative humidity. The virus-inoculated carpet coupons were applied with three chemical disinfectants or steam vapor for different contact times. The viruses on the treated carpets were subsequently recovered and titrated. Additionally, the color and tensile strength of carpets were assessed after repeated disinfection 30 times to simulate long-term use for 1.5 years. Results suggested the efficacy of disinfectants was affected by the type of carpet backing. For carpet with a water-permeable backing (Color Accent®), products A, B, and C reduced 0.8, 3.1, and 0.9 log10 PFU of FCV, and 0.3, 2.5, and 0.4 log10 TCID50 of TuV after a 30-min contact time, respectively. For the carpet with a waterproof backing (Highlight®), only product B exhibited a substantial reduction of 5.0 log10 PFU for FCV and >3.0 log10 TCID50 for TuV, while products A and C reduced 2.4 and 1.6 log10 PFU of FCV, and 1.2 and 1.2 log10 TCID50 of TuV, respectively. Impressively, steam vapor achieved a ≥5.2 log10 PFU reduction of FCV and >3.2 log10 TCID50 reduction of TuV in just 15 s on both types of carpet. Additionally, two H2O2-based disinfectants significantly impacted the tensile strength of carpet backings after repeated disinfection, with only product B causing cracks on nylon carpet fibers. The overall results highlighted the potential efficacy of steam vapor against HuNoV on both carpet types. Furthermore, one H2O2-based product (product B) exhibited efficacy on waterproof carpet, though the repeated use of disinfectants did affect some properties of the carpet.

To understand the transmission potential of SARS-CoV-2 via carpet, the persistence of SARS-CoV-2 surrogates, BCoV and HCoV OC43 on polyethylene terephthalate (PET) and nylon carpet was evaluated using both infectivity and RT-qPCR assays, and the efficacy of steam vapor treatment against BCoV and HCoV OC43 on nylon carpet was determined. After inoculation, the immediate recoveries were only 3.87% of HCoV OC43 from PET and 24.37% from nylon carpet. In contrast, the recovery rates of BCoV were 32.50% from PET and 34.86% from nylon carpet. Following a 1-h incubation at room temperature, BCoV and HCoV OC43 were reduced by 3.6 and >2.8 log10 TCID50 on PET carpet but 0.6 and 1.8 log10 TCID50 on nylon carpet, respectively. The reduction of total genomic RNA of BCoV and HCoV OC43 was also less on nylon carpet than on PET carpet, with first-order decay rates (k values) at 0.86 and 0.27 h-1 for nylon and 1.19 and 0.67 h-1 for PET carpet, respectively. These findings suggest that both surrogates were more stable on nylon than on PET carpet. For carpet disinfection, steam vapor was demonstrated as an effective method for inactivating both surrogates on nylon carpet, by reducing >3.0 log10 TCID50 of BCoV and >3.2 log10 TCID50 of HCoV OC43 within 15 s.

In response to the absence of a validated disinfection method against C. difficile endospores on carpet, this dissertation undertook a two-step approach. First, the recovery method for C. difficile endospores from the carpet was optimized by experimenting with three concentrations of Tween-80 and different stomaching durations. Subsequently, the efficacy of three EPA-registered disinfectants (two H2O2-based and one chlorine-based) and steam vapor against C. difficile endospores was evaluated on nylon carpet with two types of backing. The incorporation of 0.2% Tween-80, followed by a 3-min stomaching and subsequent sonication, substantially enhanced the recovery rate of C. difficile endospores, exceeding 60%. Product B was the most efficacious of the three disinfectants tested, which achieved reductions of 5.8 and 4.9 log10 CFU of C. difficile endospores within a 30-min contact time on carpet Highlight® and Color Accent®, respectively. Additionally, steam vapor treatment for 120 s exhibited strong efficacy, reducing >6.0 and 4.9 log10 CFUof C. difficile endospores on carpet Highlight® and Color Accent®, respectively. Additionally, combining a 120-s steam vapor treatment with a less effective product A resulted in a 6.1 log10 CFU reduction of sensitized C. difficile endospores on carpet Highlight®.

Furthermore, the efficacy of an aqueous photocatalytic disinfection system, known as photoClO2, was evaluated against HuNoV surrogates and C. difficile endospores on stainless steel and nylon carpet. The process was optimized by utilizing 1% NaClO2 and 10 ppm Eosin Y, which yielded a production rate of 60.64 ppm min-1 of ClO2 within a 4.5×4.5 cm2 area. Subsequently, the efficacy of the system was evaluated against FCV, TuV, and C. difficile endospores on both stainless steel and nylon carpet with two distinct backings under optimal lighting conditions. PhotoClO2 was efficacious in reducing>5 log10 PFU of FCV in 45 min of contact time and >3 log10 TCID50 of TuV in 60 min, but only 1.3 log10 CFU of C. difficile endospores in 120 min. On carpet Highlight®, photoClO2 achieved a 2.9 log10 PFU reduction of FCV and 2.5 log10 TCID50 reduction of TuV in 60 min, respectively, showcasing higher efficacy than carpet Color Accent® (a 1.3 log10 PFU reduction of FCV and 1.1 log10 TCID50 reduction of TuV, respectively). Under indoor lighting conditions, photoClO2 further exhibited its efficacy by inactivating 4.3 log10 PFU of FCV and 1.4 log10 TCID50 of TuV on stainless steel after 120 min. While photoClO2 proved highly effective against HuNoV surrogates, its efficacy against C. difficile endospores was limited regardless of surface material.

This dissertation provides some insights into surface disinfection strategies, with a particular focus on soft porous carpet commonly found in LTCFs and various public areas. As the alternatives to bleach, H2O2-based disinfectants exhibited efficacy against HuNoV and C. difficile endospores. The research outcomes emphasize the critical consideration of the active ingredient and product formulation when selecting disinfectants to effectively inactivate pathogens. However, the repeated use of chemical disinfectants may adversely impact carpet properties such as fiber strength and backing integrity. In comparison to chemical disinfectants, steam vapor performed well with short contact time and can be used as a more suitable option for spot treatment or routine disinfection of HuNoV, SARS-CoV-2 and C. difficile endospores for carpet. It should be noted that the efficacy of these disinfection methods can be significantly affected by the carpet backing. This suggests the significance of considering carpet construction alongside materials when selecting disinfection approaches. While photoClO2 has exhibited efficacy against HuNoV surrogates, it's necessary to emphasize that this process involves a slow yet long-lasting reaction. This specific characteristic could prove desirable in preventing the spread of pathogens between disinfection cycles. While this dissertation presented the efficacy of three types of disinfectants (chemical disinfectants, steam vapor, and photoClO2) against HuNoV and SARS-CoV-2 surrogates on carpet surfaces, the efficacy of these disinfectants should be validated using pathogenic HuNoV and SARS-CoV-2 to ensure their practical applicability.

Author ORCID Identifier

0000-0002-7466-5991

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