How is COVID-19 spread?

Author: Dr Mark Ali MBBS BSc FRCS CTh, Medical Director

Understanding how covid-19 spreads is crucial to minimising transmission, It is a highly active area of research and we are learning more daily. 

So far, we know that coronavirus is spread through droplet, aerosol and touch. It is thought to spread mainly from person to person, particularly when people are in close contact.

Droplet spread occurs when an infected person coughs or sneezes. The resulting droplets may land in the mouth, nose or eyes of people nearby, or they may be inhaled. 

Alternatively, an infected person (even showing no symptoms) may release aerosols whilst breathing and talking. Aerosols are small particle droplets containing infectious virus that can float or drift around in the air. A study published in the New England Journal of Medicine found viable aerosol particles three hours after release. 

The same study also examined spread from contact with infected surfaces. The authors found that covid-19 was more stable on plastic and stainless steel than on copper and cardboard: viable virus was detected up to 4hrs on copper, 24hrs on cardboard and 72 hrs for plastic and stainless steel.  An infected person could touch the surface or object and then another person could touch the same object and then their nose, mouth or eyes. In this way, infection can silently spread. 

This emphasises the importance of regular hand hygiene and reducing surface contact. 

Based on this science, we can implement evidence-based measures to minimise transmission, focusing on these different modes of spread. Indeed, these observations inform government policy and guidelines for creating covid-safe workplaces. 

There is evidence for alternative methods of spread. The virus may be shed in saliva (kissing can transmit) and also semen and faeces. Indeed, flushing toilets may aerosolized virus particles so you should flush the toilet with the lid shut! 

How can we reduce the spread of COVID-19?

We can reduce transmission by leveraging our knowledge of how COVID-19 spreads together with identifying those with symptoms or significant contact and isolating them and their contacts. This involves changes in our environment and behaviour together with rigorous case identification and contact tracing.