Efficacy of Dry Heat Treatment against Clostridioides difficile Spores and Mycobacterium tuberculosis on Filtering Facepiece Respirators.

The COVID-19 pandemic has required novel solutions, including heat disinfection of personal protective equipment (PPE) for potential reuse to ensure availability for healthcare and other frontline workers. Understanding the efficacy of such methods on pathogens other than SARS-CoV-2 that may be present on PPE in healthcare settings is key to worker safety, as some pathogenic bacteria are more heat resistant than SARS-CoV-2. We assessed the efficacy of dry heat treatment against Clostridioides difficile spores and Mycobacterium tuberculosis (M. tb) on filtering facepiece respirator (FFR) coupons in two inoculums. Soil load (mimicking respiratory secretions) and deionized water was used for C. difficile, whereas, soil load and PBS and Tween mixture was used for M. tb. Dry heat treatment at 85 °C for 240 min resulted in a reduction equivalent to 6.0-log10 CFU and 7.3-log10 CFU in C. difficile spores inoculated in soil load and deionized water, respectively. Conversely, treatment at 75 °C for 240 min led to 4.6-log10 CFU reductions in both soil load and deionized water. C. difficile inactivation was higher by >1.5-log10 CFU in deionized water as compared to soil load (p < 0.0001), indicating the latter has a protective effect on bacterial spore inactivation at 85 °C. For M. tb, heat treatment at 75 °C for 90 min and 85 °C for 30 min led to 8-log10 reduction with or without soil load. Heat treatment near the estimated maximal operating temperatures of FFR materials (which would readily eliminate SARS-CoV-2) did not achieve complete inactivation of C. difficile spores but was successful against M. tb. The clinical relevance of surviving C. difficile spores when subjected to heat treatment remains unclear. Given this, any disinfection method of PPE for potential reuse must ensure the discarding of any PPE, potentially contaminated with C. difficile spores, to ensure the safety of healthcare workers.

Virucidal Efficacy of Blue LED and Far-UVC Light Disinfection against Feline Infectious Peritonitis Virus as a Model for SARS-CoV-2.

Transmission of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) occurs through respiratory droplets passed directly from person to person or indirectly through fomites, such as common use surfaces or objects. The aim of this study was to determine the virucidal efficacy of blue LED (405 nm) and far-UVC (222 nm) light in comparison to standard UVC (254 nm) irradiation for the inactivation of feline infectious peritonitis virus (FIPV) on different matrices as a model for SARS-CoV-2. Wet or dried FIPV on stainless steel, plastic, or paper discs, in the presence or absence of artificial saliva, were exposed to various wavelengths of light for different time periods (1-90 min). Dual activity of blue LED and far-UVC lights were virucidal for most wet and dried FIPV within 4 to 16 min on all matrices. Individual action of blue LED and far-UVC lights were virucidal for wet FIPV but required longer irradiation times (8-90 min) to reach a 4-log reduction. In comparison, LED (265 nm) and germicidal UVC (254 nm) were virucidal on almost all matrices for both wet and dried FIPV within 1 min exposure. UVC was more effective for the disinfection of surfaces as compared to blue LED and far-UVC individually or together. However, dual action of blue LED and far-UVC was virucidal. This combination of lights could be used as a safer alternative to traditional UVC.

Control Measures for SARS-CoV-2: A Review on Light-Based Inactivation of Single-Stranded RNA Viruses.

SARS-CoV-2 is a single-stranded RNA virus classified in the family Coronaviridae. In this review, we summarize the literature on light-based (UV, blue, and red lights) sanitization methods for the inactivation of ssRNA viruses in different matrixes (air, liquid, and solid). The rate of inactivation of ssRNA viruses in liquid was higher than in air, whereas inactivation on solid surfaces varied with the type of surface. The efficacy of light-based inactivation was reduced by the presence of absorptive materials. Several technologies can be used to deliver light, including mercury lamp (conventional UV), excimer lamp (UV), pulsed-light, and light-emitting diode (LED). Pulsed-light technologies could inactivate viruses more quickly than conventional UV-C lamps. Large-scale use of germicidal LED is dependent on future improvements in their energy efficiency. Blue light possesses virucidal potential in the presence of exogenous photosensitizers, although femtosecond laser (ultrashort pulses) can be used to circumvent the need for photosensitizers. Red light can be combined with methylene blue for application in medical settings, especially for sanitization of blood products. Future modelling studies are required to establish clearer parameters for assessing susceptibility of viruses to light-based inactivation. There is considerable scope for improvement in the current germicidal light-based technologies and practices.