How COVID-19 and TB spreads

COVID-19 and TB are both respiratory infections that can be transmitted by a person with the disease who may release pathogens into the air when breathing out. These pathogens can then be inhaled into the respiratory tract of another person.

TB pathogen causes infection in humans by being inhaled or breathed in. TB pathogens are released into the air by an individual with TB disease, with the commonest route being coughing. TB pathogens are small (a droplet nuclei,<5μm in diameter) and they are small enough to remain airborne for long periods of time. TB pathogens can stay airborne for up to 6 hours, but their concentration is decreased by the movement of air (open windows, well ventilated spaces), and exposure to direct sunlight, which can kill them. As inhalation of TB bacilli can cause infection, being in close contact with someone who has TB disease, especially if they are not on an appropriate TB treatment and with symptoms such as cough, will increase the risk of being infected.

SARS-CoV-2 is larger (droplet particle, >5-10 μm in diameter) and is either inhaled if at close contact or they settle (or “drop”) onto surfaces. Studies to date suggest that the SARS-CoV-2 is mainly transmitted through contact with respiratory droplets rather than through the airborne inhalation. When someone sneezes or coughs, the droplet particles containing SARS-CoV-2 can become airborne immediately. The routes of transmission for droplet spread infections can be inhalation while drops are still airborne or when people come into contact with virus-containing droplets that fall onto a surface, usually by getting the droplets on their hands and then putting their hands to their face/mouth/nose/eyes and inhaling. The airborne route is more likely for close contacts of someone with COVID-19 or in healthcare facilities. Evidence to date shows that SARS-CoV-2 can survive on surfaces for several hours and even up to a day, which is why there is a focus on frequent and thorough handwashing to remove the virus after touching an infected surface. This is also why people should limit touching their face, in particular their mouth, nose, and eyes, all of which can serve as entry points to the rest of the body.