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Spread of the SARS-CoV-2 virus

Spread of the disease

It has been acknowledged from the early days of the outbreak that the main route of transmission is spread by droplets of saliva and mucous from people who are sneezing, coughing, shouting, singing or even just speaking. These droplets get onto the lining of the mouth, nose, eyes and the upper respiratory tract of anyone who happens to be nearby. From there, the virus can multiply rapidly within the new host. There has been controversy whether sneezing and perhaps mechanical devices in air conditioning can cause smaller particles aerosols that can drift around in the air for hours, unlike droplets that fall to the floor or nearby surfaces within a metre or two their release. Coughs and sneezes have been studied in this video. They may propel droplets for several metres before they fall to the floor.

Because the virus replicates easily in the throat, it is both easier to spread and it spreads sooner after infection than similar viruses.

Aerosol transmission in confined spaces was first suspected as a result of the cluster on the Diamond Princess cruise ship and has since been confirmed with viable virus particles lasting several hours. This confirms an earlier study from Wuhan in February.

This video explains the difference between large droplets, which fall to surfaces, and the floating aerosol particles which linger in the air, as well as the function of masks. The video is aimed at health professionals in hospital settings, although it applies to any spaces where heating and ventilating systems can produce aerosols. Have a look at this simulation from Finland.

The risk of transmission indoors can be high, as recorded in this article.Transmission by aerosol is suspected.

Research by the National Institutes of Health suggests that droplets and aerosol particles are expelled by speech alone. This implies that singing and shouting could promote the spread of the disease, underlined by case studies of "superspreader" events such as choir practice and church services. It all backs up an early study from The New England Journal of Medicine

According to a study by the National Institute of Diabetes and Digestive and Kidney Diseases these aerosol particles can hang in the air for up to 14 minutes. Other studies have suggested a much longer suspension time, depending on conditions. Opening windows for a good air flow helps disperse the particles!

It is now understood that the risks of contracting the disease from infected surfaces is lower than previously thought, it remains a potential source of infection and we should continue with scrupulous handwashing and disinfecting surfaces, although it is now clear that surfaces are a minor a minor route to infection, unless heavily and freshly contaminated.

Air travel is considered safe at present, cabin ventilation systems have HEPA filters which will allow the extraction of air viral particles.

Also, outdoors, aerosols are quickly dispersed on the breeze. Both sunshine (UV light) and rainfall will act to reduce the risk. Since the beginning of the outbreak, Chinese doctors have been advising those indoors to keep windows open and not use air conditioning. Relocating social activities to the outdoors was an important factor in controlling the deadly Spanish Flu pandemic of 100 years ago, when the disease spread in a similar way to today.

Hospitals and care homes in the UK have provided an important reservoir of the disease during the outbreak. This got so bad at Weston General Hospital that it was closed in May of this year. Tests showed that 100 workers at the hospital tested positive for the virus and 40 per cent of the staff at one point were infected. 20 per cent patients were infected while at the hospital.

This irony, of hospitals spreading the disease, has been mainly due to poor protection of auxiliary staff such as cleaners and office workers. At least 540 health and social care workers have died from COVID-19 in England and Wales alone, the UK is second only to Russia in this league table.

540 is over seven times the number of people who died in the Grenfell Tower fire in 2017. No amount of saucepan banging is going to bring any of them back to life. We consider it the duty of each citizen to help in practical ways to prevent further loss of life in the caring professions, by slowing the spread of the disease. Taking risks with it can lead to others being killed by it and this fact is on our minds as we all seek to get "back to normal".

Talking about the indoor environment in general terms, Prof Anthony Costello(ex Director WHO) reports "The longer those infected individuals spend in that space, the higher the concentration of virus in the air over time. This is particularly bad news for spaces where people congregate for hours on end, like restaurants, bars, offices, classrooms, and churches."

Many health professionals [advise against attending pubs and gyms] during the pandemc. i "Even for those being careful, gyms pose a risk. Many are indoors, where ventilation is limited and social distancing can be challenging."


All the above information is consistent with SARS-CoV-2 as a contagious airborne disease, suggesting that generic precautions (tuberculosis, SARS-1 etc) will be effective even though specific information on this precise virus is unavailable.

What we know about the virus

The spread of SARS-CoV-2

Staying safe

What we still don't know about the virus

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