key: cord-341069-kngf6qpe
authors: Chan, Kwok-Hung; Sridhar, Siddharth; Zhang, Ricky Ruiqi; Chu, Hin; Fung, Agnes Yim-Fong; Chan, Gabriella; Chan, Jasper Fuk-Woo; To, Kelvin Kai-Wang; Hung, Ivan Fan-Ngai; Cheng, Vincent Chi-Chung; Yuen, Kwok-Yung
title: Factors affecting stability and infectivity of SARS-CoV-2
date: 2020-07-09
journal: J Hosp Infect
DOI: 10.1016/j.jhin.2020.07.009
sha: 
doc_id: 341069
cord_uid: kngf6qpe

BACKGROUND: In late 2019, a novel human coronavirus, SARS-CoV-2, emerged in Wuhan, China. This virus has caused a global pandemic involving more than 200 countries. SARS-CoV-2 is highly adapted to humans and readily transmits from person-to-person. AIM: The aim of this study was to investigate the infectivity of SARS-CoV-2 under various environmental factors, disinfectants and different pH conditions. The efficacy of a variety of laboratory virus inactivation methods and home disinfectants against SARS-CoV-2 were investigated. METHODS: The residual virus in dried form or in solution was titrated on Vero E6 cell line at day 0, 1, 3, 5, and 7 after incubation at different temperatures. The viability of virus was determined after treatment with different disinfectants and pH solutions at room temperature (20∼25(o)C). FINDINGS: SARS-CoV-2 was able to retain viability for 3-5 days in dried form or 7 days in solution at room temperature. SARS-CoV-2 could be detected under a wide range of pH conditions from pH4 to pH11 for several days and 1 to 2 days in stool at room temperature but lost 5 logs of infectivity. A variety of commonly used disinfectants and laboratory inactivation procedures were found to reduce viral viability effectively. CONCLUSION: This study demonstrates the stability of SARS-CoV-2 on environmental surfaces and raises the possibility of faecal-oral transmission. Commonly used fixatives, nucleic acid extraction methods and heat inactivation were found to significantly reduce viral infectivity that could ensure hospital and laboratory safety during the COVID-19 pandemic.

Ten µl of virus (SARS-CoV-2, 10 6.5 TCID50/ml; SARS-CoV-1, 10 7 TCID 50 /ml) was placed on 103 a glass slide within a shell vial, kept at room temperature (20~25 o C and relative humidity of 104 63%) and allowed to dry according to our previous study with slight modifications (6). One 105 hundred microliters of MEM were used to re-suspend the virus for 0, 1, 3, 5, and 7 days after Viral transport medium with different pH from 2 to 13 using 5M and 1M HCl or 5N and 1N 113 NaOH were prepared as described (9). One hundred microliters of SARS-CoV-2 with 114 10 6.5 TCID 50 /ml was added into each bottles of 0.9 ml VTM and incubated at room temperature 115 (20-25 o C). All the tests were done in triplicates. The viability of virus was tested on day 1, 116 day 3 and day 6. On each testing day, the pH of the VTM bottles were neutralized to pH 7 and 117 viral titre was measured using the TCID50 assay (8). An untreated virus stock solution as the 118 viral load for the positive control was included. Thirty microlitres of SARS-CoV-2 (10 6.5 TCID 50 /ml) and 270 µl of various disinfectants were 130 mixed and incubated at room temperature (Table 1) Thirty microlitres of SARS-CoV-2 (10 5.5 TCID 50 /ml) and 270 µl of FBS were mixed and 139 incubated at 56°C for 30min. then, the residual infectivity of the virus was determined by 140 TCID50 assay as described above. The test was set up in triplicates. When SARS-CoV-2 was added in VTM with pH ranging from 2 to 13, the virus remained 163 viable up to 6 days but lost between 2.9 and 5.33 logs of infectivity from pH5 to pH9 and up 164 to 1~2 days in pH4 and pH11 ( Table 2) . The virus lost infectivity within 1 day at pH extremes 165 (pH2~3 and pH11~12). The virus lost 5.25 logs of infectivity in stool over a 3-day period.

Laboratory or domestic disinfectants, including two commonly used as a lysis buffer for 168 nucleic acid extraction, were tested for their effects on SARS-COV-2 on Vero E6 (Table 3) . 169 Due to the cytotoxicity of certain disinfectants, detection limit of inactivation had been found All tests were neutralized before testing and was set up in triplicates. 

Negative (6.50±0.00) Negative (6.50±0.00) ND

Untreated virus stock solution as the viral load for the positive control

All tests were neutralized before testing and conducted in triplicates