Physical transport (droplets) and aerosol inhalation
Covid-19 is respiratory infection caused by the SARS-CoV-2 virus, which can affect the upper and lower respiratory tract. SARS-CoV-2 is an opportunistic airborne pathogen that infects cells expressing the ACE-2 enzyme, the host cell receptor for viral entry. Airborne respiratory infections may be transmitted by direct inhalation into the respiratory tract, or introduced into the oro/naso-pharynx by hand, or following ocular exposure and transmission through tear ducts. Neither the relative importance of, nor the minimum infectious dose of SARS-CoV-2 virus for the different pathways of infection transmission are known.