SARS-CoV-2 viability after exposure to titanium dioxide coated tiles

Background Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)
transmission occurs via airborne droplets and surface
contamination. Droplets or other body fluids from infected
individuals can contaminate surfaces and viable virus has been detected on
such surfaces, including surgical masks, for hours, even days depending on
different factors including humidity, temperature and type of
surface. Titanium dioxide (TiO2) coating of surfaces is a
promising infection control measure, though to date has not been tested
against SARS-CoV-2. Methods Virus stability was evaluated on the
following surfaces: sterile untreated Sterilin standard Petri
dish; TiO2- and TiO2–Ag (Ti:Ag atomic ratio 1:0.04)-coated 45 x 45 mm
ceramic tiles. After coating the tiles were stored for 2–4 months before
use. Surfaces were exposed (610 lx, ambient laboratory light) for 1 h
before the start of each experiment to ensure a steady state of radical
generation. We tested the stability of both SARS-CoV-2 Spike pseudotyped
virions based on a lentiviral system, as well as fully infectious
SARS-CoV-2 virus (SARS-CoV-2/human/Liverpool/REMRQ0001/2020). For the
former, tile surfaces were inoculated with 105RLU of SARS-CoV-2 spike
pseudotyped HIV-1 luciferase virus at time t = 0 and
illuminated for up to 6 h. At intervals virus was recovered from surfaces
with DMEM complete followed by infection of ACE-2/TMPRSS2-expressing 293T
cells. For live virus,  after illuminating
tiles for 0–300 min virus was recovered from surfaces followed by
infection of Vero E6 cells. % of infected cells was determined by flow
cytometry detecting SARS-CoV-2 nucleocapsid protein 24 h
post-infection.  Results After 1 h illumination the
pseudotyped viral titre was decreased by four orders of
magnitude. There was no significant difference between
the TiO2 and TiO2–Ag coatings. Light alone had no
significant effect on viral viability. For live SARS-CoV-2, virus
was already significantly inactivated on the TiO2 surfaces after
20 min illumination. After 5 h no detectable active virus
remained. Significantly, SARS-CoV-2 on the untreated surface was still
fully infectious at 5 h post-addition of virus. Overall, tiles
coated with TiO2 120 days previously were able to inactivate
SARS-CoV-2 under ambient indoor lighting with 87% reduction in titres at
1h and complete loss by 5h exposure. Conclusions In the context of
emerging viral variants with increased transmissibility,
TiO2 coatings could be an important tool in containing
SARS-CoV-2, particularly in health care facilities where nosocomial
infection rates are high.