1 | INTRODUCTION
The new variance of SARS-CoV-2 has a 43% to 90% higher reproduction number than the existing variants(Davies et al., 2021). Possible transmission routes include airborne particles, respiratory droplets, and contact with a contaminated surface. Interrupting the chain of the transmission routes is vital to limit the spread of the virus. One of the inactivation methods is high-temperature exposure of contaminated surfaces or liquids, which has been reported previously(Darnell et al., 2004; Hessling et al., 2020; Liu, 2004). Heat inactivation of SARS-CoV-2 has mainly been used to sterilize contaminated personal protective equipment such as masks and gloves in hospitals and contaminated equipment and liquids in laboratories before reuse(Abraham et al., 2020; Batéjat et al., 2021; Biryukov et al., 2021).
SARS-CoV in liquid was inactivated in 45 minutes and 75 minutes at a temperature of 75 oC and 56 oC, respectively(Darnell et al., 2004). A 4 log10 TCID50 reduction was observed with a heat treatment protocol of 60oC - 60 min and 92 oC - 15 min(Pastorino et al., 2020). Using the SARS-CoV and SARS-CoV-2 data from different studies, the time required for 5 log10-reduction was estimated as 32.5, 3.7, and 0.5 minutes for temperatures of 60 oC, 80oC, and 100 oC(Hessling et al., 2020). A 6 log10 TCID50 reduction was obtained within a fluidic system within 1.03 s at a temperature of 83.4 oC(Jiang et al., 2021). Nevertheless, dry heat inactivation of aerosolized SARS-CoV-2 has not been investigated yet.
During the Covid-19 pandemic, exposure to indoor aerosolized SARS CoV-2 has become one of the primary challenges (Chia et al., 2020; Morawska et al., 2020). Heat inactivation of the aerosolized SARS-CoV-2 is one way to reduce the spread of 2019 coronavirus disease (COVID-19). In the present study, the inactivation of SARS-CoV-2 at high air temperatures of 150 oC and 220 oC has been investigated using an experimental setup, while minimizing potential hazards.
2 | MATERIALS AND METHODS
Preparation of SARS-CoV-2 Suspensions Experiments were performed in biosafety level 3 (BSL3) facilities, using a stock suspension of SARS-CoV-2 strain (Gen Bank No: MT955161.1). SARS-CoV-2 virus stock was prepared by inoculating the Vero E6 cell line in Dulbecco’s modified Eagle’s medium (DMEM-10). Dulbecco’s modified Eagle’s medium containing supplements (10% fetal bovine serum, 2nM/ml L-glutamine, 100 U/ml penicillin, 100 mg/ml streptomycin, and 0.5 mg/ml fungizone (Amphotericin B)) was added to the flask, and the cells were incubated at 37oC for 72 h. The supernatant was collected, clarified by centrifugation, and stored at -80oC. TCID50 titer was determined by the Spearman- Kärber method as described(Hubert, 1984).
Experimental Setup for Heat Inactivation of SARS-CoV-2 The experimental system is shown in Fig.1, consisted of an air compressor with an air flow rate of 0.6 m3/h (10 L/min), an electric heater (600 Watt), a venturi injector, an air flow meter (RST Measurement Control Tech., Istanbul, Turkey), a nebulizer (M102, Jiangsu Yuyue Medical Equipment & Supply Co., Ltd., Danyang Jiangsu, China) with a nebulization rate of 0.2 mL/min, with an average particle size of 3.7 microns, an inline polycarbonate filter holder with a gelatin membrane filter (Sartorius, Göttingen, Germany), a thermometer with k-type thermocouple (CEM-613, CEM, Shenzhen, China), and an aspirator (Ecoaspir, Kare Medical, and Analytical Devices Ltd. Co., Ankara, Turkey ) for vacuuming. Suspension of the SARS-CoV-2 was nebulized into the venturi injector and mixed with the compressor’s air before entering the electric heater. The temperature of the air increased through the heater. Since the gelatin filter’s maximum working temperature was 60oC, the silicone house connected the heater’s outlet and the filter holder wound around the ice to reduce the temperature below 60 oC. The aspirator with an airflow of 0.6 m3/h was connected to the filter holder output and used as a vacuum pump.