key: cord-1052518-rh0j2hja
authors: Bormann, M.; Alt, M.; Schipper, L.; van de Sand, L.; Otte, M.; Meister, T. L.; Dittmer, U.; Witzke, O.; Steinmann, E.; Krawczyk, A.
title: Disinfection of SARS-CoV-2 contaminated surfaces of personal items with UVC-LED disinfection boxes
date: 2021-03-04
journal: bioRxiv
DOI: 10.1101/2021.03.03.433725
sha: 7e5f0bad1065177bbc8986322c29448374c1fc88
doc_id: 1052518
cord_uid: rh0j2hja

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is transmitted from person-to-person by close contact, small aerosol respiratory droplets and potentially via contact with contaminated surfaces. Here, we investigated the effectiveness of commercial UVC-LED disinfection boxes in inactivating SARS-CoV-2 contaminated surfaces of personal items. We contaminated glass, metal and plastic samples representing the surfaces of personal items such as smartphones, coins or credit cards with SARS-CoV-2 formulated in an organic matrix mimicking human respiratory secretions. For disinfection, the samples were placed at different distances from UVC emitting LEDs inside commercial UVC-LED disinfection boxes and irradiated for different time periods (up to 10 minutes). High viral loads of SARS-CoV-2 were effectively inactivated on all surfaces after 3 minutes of irradiation. Even 10 seconds of UVC-exposure strongly reduced viral loads. Thus, UVC-LED boxes proved to be an effective method for disinfecting SARS-CoV-2 contaminated surfaces that are typically found on personal items.

SARS-CoV-2 working stocks (5 × 10 6 TCID50/mL for UVC-LED box 1; 2 x 10 6 TCID50/mL for UVC-86 LED box 2) were diluted in a defined organic matrix mimicking respiratory secretions (9). In brief, 87 900 µL of the respective virus stock was added to 100 µL organic matrix consisting of 2.5 mg/mL 88 mucin type I-S, 7.8 mg/mL BSA Fraction V and 11 mg/mL yeast extract (all Sigma-Aldrich, 89

Darmstadt, Germany). Before inoculating the respective virus suspension to glass, metal and 90 plastic carriers, the carriers were sterilized with a UV-lamp emitting 1940 µW/cm 2 UVC at 254 nm 91 (UV-4 S/L, Herolab, Wiesloch, Germany) (7). After sterilizing, 50 µL of the respective virus 92 suspension were placed on the center of the carriers and allowed to dry for 1 h at room 93 temperature. The carriers were positioned at different distances from the UVC-LEDs inside the 94 UVC-LED boxes (UVC-LED box 1: 1 cm and 5 cm horizontal distance; UVC-LED box 2: 1 cm and 95 4 cm vertical distance). The carriers were irradiated for specific durations (0 s, 10 s, 30 s, 1 min, 96 3 min and 10 min). Subsequently, the infectious virus was recovered by vortexing the carriers 97 placed in plastic containers (SARSTEDT, Nümbrecht, Germany) filled with 2 mL DMEM for 1 98 minute. As control, the virus was recovered 10 minutes after drying without irradiation. The 99 experiments were conducted in triplicates and the viral loads were determined by endpoint dilution 100 according to Spearman and Kärber. The means, standard deviations of the viral titers and 90% 101 effective concentration (EC90) values were calculated with GraphPad Prism 9 (GraphPad 102 Software, San Diego, CA). The statistical significances were determined with the t-test. 103

Comparisons were considered significant at * P < 0.05; * * P < 0.01; and * * * P < 0.001. 104 105

SARS-CoV-2 can potentially be transmitted via virus-contaminated surfaces of personal items 107 such as smartphones, keys, coins or credit cards that have been contaminated with the virus. We 108 investigated the performance of two commercially available UVC-LED boxes for virus inactivation 109 on surfaces typically found on personal belongings such as glass, metal and plastic. We used two 110 different UVC-LED boxes for sterilizing, one with lateral UVC-LEDs (Fig. 1A) and one with UVC-111

LEDs incorporated in the lid of the box (Fig. 1B) . Additionally, a mirror was installed to the bottom 112 of the chamber. For UVC-LED box 1, the emitted light intensity was determined with 245 µW/cm 2 113 at horizontal distance of 1 cm and 65 µW/cm 2 in the center of the box at horizontal distance of 5 114 cm from the UVC-LEDs (Corresponding to 0.245 mJ/cm 2 and 0.065 mJ/cm 2 per second, 115 respectively; Fig. 2A ). For both distances, the peak wavelength emission was measured at around 116 254 nm. For UVC-LED box 2, the emitted light intensity was measured with 117 µW/cm 2 at 1 cm 117 vertical distance from the LEDs, which corresponds to 0.117 mJ/cm 2 per second (Fig. 2B ). The 118 peak wavelength emission was detected at 280 nm. 119

Next, metal, glass or plastic samples were overlaid with SARS-CoV-2 diluted in an organic matrix 120 mimicking respiratory secretions. The final calculated virus concentration on the samples was 4.5 121 × 10 6 TCID50/mL for UVC-LED box 1 and 1.8 x 10 6 TCID50/mL for UVC-LED box 2, respectively. 122

Compared to the viral load immediately after drying, there was no significant reduction of the viral 123 loads after 10 minutes without irradiation (Fig. 3) . 124 UVC-LED irradiation conducted with UVC-LED boxes proved to be an appropriate method for the 125 disinfection of SARS-CoV-2 contaminated surfaces. SARS-CoV-2 contaminated glass, metal or 126 plastic samples were effectively UVC-disinfected inside of both UVC-LED boxes ( Fig. 3 and 4) . A 127 significant reduction of viral loads of SARS-CoV-2 on glass, metal and plastic was achieved even 128 after 10 seconds of irradiation (UVC-LED box 1: 2.45 mJ/cm 2 ; UVC-LED box 2: 1.17 mJ/cm 2 ) at 129 a distance of 1 cm from the LEDs in both UVC-LED boxes (Fig. 3) . When using UVC-LED box 1, 130 complete inactivation of SARS-CoV-2 could be achieved after 3 (glass and plastic) or 10 minutes 131 (metal) of irradiation at a distance of 1 cm ( Fig. 3A and 4A) . At a distance of 5 cm from the LEDs 132 with other studies that report susceptibility of coronaviruses, including SARS-CoV-1 and SARS-155

CoV-2 to UVC irradiation (7, 10). To almost completely inactivate high viral loads of SARS-CoV-156 1, a UVC-dose of 1446 mJ/cm 2 was necessary (10). High viral loads of SARS-CoV-2 could be 157 completely inactivated by a UVC dose of 1048 mJ/cm 2 (7). The results of the present study show 158 that the distance of the inoculated materials from the LEDs and thus the emitted light intensity is 159 a decisive factor for achieving the complete inactivation of SARS-CoV-2. Accordingly, recently it LEDs. Light doses at 4 cm distance cannot be shown, as an irradiance measurement of the LEDs 224 at that distance would have required drilling a hole into the bottom of the box, which was not 225 possible without damaging the box. Data are displayed as mean ± SD. * P < 0.05; * * P < 0.01; and 226 

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