El Pais has an interesting visualisation of how aerosol transmission works in indoor settings. It’s one of those things that you read and then wish you hadn’t because it makes the world just a little more terrifying.
Aerosol transmission is different from droplet transmission. The latter happens when someone coughs or sneezes at you. The droplets generally don’t travel far but infect if they come into contact with the eyes, nose or mouth. Aerosol transmission is by way of tiny particles, which are light enough to travel in air currents. They can stay in the air for hours, floating around and increasing in concentration until they are dispersed (or inhaled).
It’s always seemed to me that aerosol transmission is understated in the UK response to COVID-19. Bars and restaurants have been allowed to remain open, and many people are now working in offices again – albeit with reduced numbers and preventive methods such as barrier screens and temperature checks. But if you’ve got an infected person in a room with 20 other people, with poor ventilation, none of the standard prevention makes any difference. The air will be full of aerosol droplets.
There’s still a couple of unknowns. We know that aerosol transmission happens, but we don’t know how much it is contributing to the wider spread. We know that ventilation helps, but we don’t know whether HVAC systems help or not.
The mitigation is straightforward:
- Don’t stay anywhere indoors longer than you need to, ideally no longer than an hour
- Make sure your destination is well ventilated, preferably through open windows/doors but at the very least through mechanical ventilation
- Wear a mask when you can
- Try to do things outdoors instead