15 weeks into the COVID-19 pandemic, scientists know a lot more about how the disease is transmitted.
The highest risk for public health is from crowded indoor spaces with poor ventilation, and especially with
prolonged face-to-face interactions. In close proximity, people speaking, coughing, singing, or simply
breathing can produce respiratory droplets containing the COVID-19 (SARS-CoV-2) virus. These droplets
may land on the nose, mouth or eyes of another person close by.
There is also increasing consensus that some droplets may become aerosolized, and hang about in the air. One study due to be published found that SARS-CoV-2 survives aerosolization better than other coronaviruses and maintains infectivity in aerosols for at least 16 h. Strong air conditioners or fans can spread these droplets further within an enclosed space. Last week, a review article published in Science stated that 'a large proportion of the spread of coronavirus disease 2019 (COVID-19) appears to be occurring through airborne transmission of aerosols produced by asymptomatic individuals during breathing and speaking' and that therefore 'For society to resume, measures designed to reduce aerosol transmission must be implemented'.
Droplets may also land on surfaces. Although surface contamination generally has a much lower risk than
airborne particles, studies show that the virus can stay active on plastic and metal for up to 7 days. The
highest risk comes from high-contact furnishings such as door handles, toilet flushes, handrails, payment
terminals, lift/elevator buttons, and, ironically, hand sanitiser dispensers and protective screens. Flushing toilets can also 'create clouds of virus-containing particles', according to recent research published in Physics of Fluids.
Outdoors, where people can usually distance themselves from each other more effectively, the risk is
greatly reduced. Air movement helps to dilute virus-carrying droplets. Critically, hydroxyls are also
abundant in outdoor air, especially in conditions with lots of sunlight and humidity, and these powerful
molecules continually inactivate viruses in the air and on surfaces. However, indoors is where most of us
live, work, do errands like shopping, and spend a lot of our leisure time; realistically, we can’t avoid being
near other human beings, and most of us don’t want to!
Masks, distancing, increased hygiene, and other behavioural changes can all help reduce risks, and of
course medical researchers are working urgently to develop vaccines and effective treatments. However,
other long-term solutions are needed to help us get us back to, and continue to enjoy, our normal way of
life. We’re proud to have developed the world’s first products to provide 24/7 decontamination of entire
indoor spaces - air and surfaces - so people can safely get on with their lives.
Reducing transmission of SARS-CoV-2 - Science, 26 June 2020
How Exactly Do You Catch Covid-19? There Is a Growing Consensus - Wall Street Journal, 16 June
At work, school and seeing friends: How to lower your coronavirus risk - New Scientist, 27 May 2020
Dr Wyatt blogs on his lifetime's experience of Indoor Air Quality Issues.