key: cord-1051291-ddouxod1
authors: Heilingloh, Christiane Silke; Aufderhorst, Ulrich Wilhelm; Schipper, Leonie; Dittmer, Ulf; Witzke, Oliver; Yang, Dongliang; Zheng, Xin; Sutter, Kathrin; Trilling, Mirko; Alt, Mira; Steinmann, Eike; Krawczyk, Adalbert
title: Susceptibility of SARS-CoV-2 to UV Irradiation
date: 2020-08-04
journal: Am J Infect Control
DOI: 10.1016/j.ajic.2020.07.031
sha: 19cf425a4d28a9503b35a345c679b1cc5531f485
doc_id: 1051291
cord_uid: ddouxod1

The coronavirus SARS-CoV-2 pandemic became a global health burden. We determined the susceptibility of SARS-CoV-2 to irradiation with ultraviolet light. The virus was highly susceptible to ultraviolet light. A viral stock with a high infectious titer of 5 × 10(6) TCID(50)/ml was completely inactivated by UVC irradiation after nine minutes of exposure. The UVC dose required for complete inactivation was 1048 mJ/cm(2). UVA exposure demonstrated only a weak effect on virus inactivation over 15 minutes. Hence, inactivation of SARS-CoV-2 by UVC irradiation constitutes a reliable method for disinfection purposes in health care facilities and for preparing SARS-CoV-2 material for research purpose.

The coronavirus SARS-CoV-2 pandemic became a global health burden. We determined the susceptibility of SARS-CoV-2 to irradiation with ultraviolet light. The virus was highly susceptible to ultraviolet light. A viral stock with a high infectious titer of 5 x 10 6 TCID 50 /ml was completely inactivated by UVC irradiation after nine minutes of exposure. The UVC dose required for complete inactivation was 1048 mJ/cm 2 . UVA exposure demonstrated only a weak effect on virus inactivation over 15 minutes. Hence, inactivation of SARS-CoV-2 by UVC irradiation constitutes a reliable method for disinfection purposes in health care facilities and for preparing SARS-CoV-2 material for research purpose.

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In December 2019, a novel coronavirus causing severe acute respiratory disease (SARS-CoV-2) was newly identified in the Hubei province, PR China, before becoming a global pandemic and causing tremendous health and socio-economic burdens 1 . At the time of writing, more than 14.9 million cases and >618,000 deaths were reported worldwide (2020.07.23). The actual number of people infected with SARS-CoV-2 is most likely to be much higher since numerous infections, especially in younger people, are asymptomatic and frequently not captured by routine diagnostic methods 2 . The symptoms of COVID-19 range from mild respiratory illness accompanied by cough, fever, myalgia, and fatigue, to severe, life-threatening pneumonia and acute respiratory distress syndrome (ARDS) 3 . Clearly, the prevention of the transmission of respiratory infections especially within hospitals or other institutions is of central importance. The disinfection of objects using UV-irradiation is an environmentally friendly method of killing bacteria, fungi and viruses without the use of harmful chemicals or heat. Consequently, UV light disinfection is becoming increasingly applied in healthcare facilities for disinfecting healthcare equipment, surfaces and operating rooms 4 . However, the efficacy of UV irradiation on the inactivation of SARS-CoV-2 in fluids has not been described thus far. In the present study, we investigated the susceptibility of high titer viral stocks of SARS-CoV-2 to combined or separate UVA and/or UVC irradiation.

A clinical isolate of SARS-CoV-2 was isolated from a nasopharyngeal swab of a patient suffering from COVID-19 disease. The patient was hospitalized at the Department of Infectious Diseases of the University Hospital Essen. The swab was taken using a Virocult® vial (Sigma, Germany). The Virocult® medium was then incubated on Vero E6 cells cultured in DMEM containing 10% (v/v) fetal calf serum and supplemented with Penicillin (100 IU/ml), Streptomycin (100 µg/ml), Ciprofloxacin (10 µg/ml) and Amphotericin B (2.5 µg/ml). After five days of incubation, the supernatant was harvested and cell debris was removed by centrifugation. Afterwards, 100 µl of the clear supernatant was used for subsequent infection of a new Vero E6 cell culture flask. After five days of incubation, supernatants were found to be positive for SARS-CoV-2 by a conventional qualitative PCR. The virus suspension was harvested and cleared from cellular debris by centrifugation and stored at -80°C. Viral titers were determined by endpoint dilution assay and the 50% tissue culture infective dose (TCID 50 ) was calculated.

To determine the susceptibility of SARS-CoV-2 to UVA and/or UVC irradiation, a viral stock at a concentration of 5 x 10 6 TCID 50 /ml was irradiated with UV light for up to 30 minutes. UVA were taken after 0, 3, 6, 9, 12, 15 minutes, and after UVC-irradiation after 0, 1, 2, 3, 6, 9

and 15 minutes. The TCID 50 /ml concentration of each sample was determined by endpoint dilution, respectively.

at a concentration of 5 x 10 6 TCID 50 /ml was achieved after 9 minutes of combined UVA and UVC exposure ( Figure 1A) . As calculated by nonlinear regression, 50% of the virus could be inactivated after 1.4 minutes of UV-treatment ( Figure 1B) . UVA exposure alone was less effective on virus inactivation. After 9 minutes of irradiation and an emitted dose of 292 mJ/cm 2 , one log reduction of the viral load was observed. In contrast, complete virus inactivation was achieved after a 9 minute exposure to UVC and an emitted UVC dose of 1048 mJ/cm 2 . These data confirm former findings that UVC is more effective in inactivating viruses, and highlight UVC irradiation as an effective method for the inactivation of SARS-CoV-2.

In the present study, we demonstrated that SARS-CoV-2 could effectively be inactivated by UVC irradiation, even at high viral titers, whereas UVA-irradiation was much less effective.

These data are in line with previous reports where other coronaviruses e.g. SARS-CoV-1 were shown to be susceptible to UVC irradiation [5] [6] [7] . Viral stocks with titers of 1 x 10 6 TCID 50 /ml of SARS-CoV-1 could be almost completely inactivated after 6 minutes of UVC-irradiation, corresponding to a UVC dose of 1446 mJ/cm 2 5 . In our study, the emitted dose required for a complete inactivation of SARS-CoV-2 was 1048 mJ/cm 2 after 9 minutes of exposure. A similar dose of 1 J/cm 2 was also required to inactivate a viral load of 1 * 10 6 TCID 50 H1N1 influenza virus 7 . UV light disinfection is chemical free and thus a suitable method for applying in healthcare facilities to disinfect healthcare equipment 4 . Most recently, a protocol for the disinfection of personal protective equipment (PPE) including filtering face pieces from health care workers described the potential use of ultraviolet light to inactivate SARS-CoV-2 6 . Taken together, we demonstrated that UV irradiation is a highly effective method to inactivate the new corona virus SARS-CoV-2, even at the higher viral load levels that are found in research laboratories e.g. in cell-culture supernatants or in diagnostic material taken from the respiratory tract of COVID-19 patients.

UVC irradiation, revealing that this method is reliable not only for disinfection purposes in health care facilities but also for preparing inactivated SARS-CoV-2 material for research. 

A Novel Coronavirus from Patients with Pneumonia in China

Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS-CoV-2)

Clinical Characteristics of Coronavirus Disease 2019 in China

Evaluation of an Ultraviolet C (UVC) Light-Emitting Device for Disinfection of High Touch Surfaces in Hospital Critical Areas

Inactivation of the coronavirus that induces severe acute respiratory syndrome, SARS-CoV

Rapid evidence summary on SARS-CoV-2 survivorship and disinfection, and a reusable PPE protocol using a double-hit process

Research to Mitigate a Shortage of Respiratory Protection Devices During Public Health Emergencies. Applied Research Associates

This study was supported by the Stiftung Universitätsmedizin Essen (awarded to K. Sutter, M. Trilling and A. Krawczyk) and the Rudolf Ackermann Foundation (awarded to O. Witzke).The authors thank Delia Cosgrove for the proofreading of the manuscript. Steinmann, A. Krawczyk study design, writing, figure design.

The authors declare no conflict of interest.