As the global COVID-19 pandemic marches on, we are learning more about the SARS-CoV-2 virus transmission, ie how does the virus spread.

It is now conclusively understood that the virus enters the body primarily through the respiratory tract. The predominant mode of spread appears to be from person to person. The mechanism of spread is from respiratory secretions which can emanate from the mouth or nose of an infected person. It is important to note that an infected person who does not have symptoms can still spread the SARS-CoV-2 virus. The body secretions predominantly involved include saliva, respiratory secretion, and secretion droplets. These are produced when an infected persons coughs, sneezes, speaks or sings. Generally, there are several factors that influence the risk of getting infected when in the presence of an infected person. Acquiring an infection usually means exposure to virus particles in a sufficient number to overwhelm the defences of body and establish an infection.

We can think of disease transmission occurring in 2 main ways.

What do we know about direct spread/aerosolised spread?

Direct spread occurs in the presence of someone who is infected with the SARS-CoV-2 virus. A person who is infected will expel respiratory secretions which then enters the body of an uninfected individual most commonly through the mouth or nose but potentially through the membranes of the eyes. Aerosolised spread refers to the fact that in certain circumstances, virus particles may float in the air for significant periods of times (minutes to hours) instead of falling to the ground.

When virus particles are expelled during speech, singing, sneezing or coughing, they are usually combined with either solid or fluid matter and occur in a range of sizes. The larger the size of the particles the more likely that they are to fall to the ground. Virus containing particles at the lower end of the range have a greater chance of remaining airborne for significant periods of time. Early in the COVID-19 pandemic, the conventional wisdom was that most cases of transmission via airborne particles occurred in medical settings with patient who were undergoing medical procedures such as intubation, endoscopy, etc. More recently there has been greater concern of aerosolised transmission among the general population in poorly ventilated indoor spaces.

There are several factors that play a role in the transmission of infection. One factor that has been somewhat controversial recently has been a question of what is a safe distance for social/physical distancing? From the outset, we should point out that there are no randomised controlled studies looking at distance vs the risk of infection for COVID-19. The recommendations are made from imperfect studies and expert judgement. A seminal study of tuberculosis droplets done in the 1930s suggested that these droplets would fall to the ground within three feet.

Another observational study was published in the New England Journal of Medicine in 2005 during the SARS epidemic. Three airline flights that had people infected with the SARS virus were reviewed. It was found that transmission could be demonstrated up to six feet from the infected individual. Since the onset of the COVID-19 epidemic, further data has come from studies of fluid dynamics suggesting that under the right conditions, respiratory droplet travel can reach 23-27 feet. There has been anecdotal support for this in a study of transmission among three families in a poorly ventilated Chinese restaurant and possibly from a cluster of infections related to choir practice in a church in Seattle. It has, however, proved difficult to retrieve live/infectious virus particles from indoor air.

The absence of good randomised data is reflected in the current recommendations of the World Health Organization (WHO) and the European Centers for Disease Control (CDC) for social distancing at three feet and the American CDC which recommends six feet. With this uncertainty, what should our population do? There are some general rules of thumb to guide us. Generally, it is a good idea to maintain some distance from others in society. We cannot know who is infected simply by looking. Our Ministry of Health and Wellness recommends a social distancing of six feet. Generally, it is better to be in a well-ventilated area. Being outside ensures that there is a constant circulation of fresh air. If you are inside, opening windows is one method to improve air circulation. In places with central air conditioning, using good filtration systems that allow removal of virus particles from the air and ensuring an adequacy of air exchange/fresh air intake. Attempts should also be made to avoid crowding as far as it is possible.

Are you at risk

Indirect spread is thought to be a less common method of spread. This involves SARS-CoV-2 particles that contaminate the environment. In this scenario, infected individuals may cough or sneeze or otherwise transfer virus particles to surfaces in the environment. It has been documented that the SARS-CoV-2 virus can survive for varying periods on different surfaces (Up to 2-3 days for plastics and metals). How infectious the virus particles are after prolonged periods remains unclear. Individuals touching the contaminated surfaces and then their own face can transfer virus to the mouth or nose resulting in infection. It is thought that this is uncommon, and the risk can be mitigated by frequent cleaning of public areas with alcohol-based cleansers, frequent hand washing with soap and avoiding touching our faces when out in public. Using a mask also helps in this regard as it can serve both as a reminder and a barrier to face touching. The risk of indirect contact with SARS-CoV-2 remains a concern with dining at restaurants. This can, however, be mitigated by frequent cleaning of surfaces by restaurant staff and also limiting the number of guests seated inside the restaurants and seating diners outside in an open space if possible, still maintaining appropriate and safe seating distances consistent with established guidelines.

A word or two

An additional level of protection that can be employed to reduce direct spread on a societal level is the universal use of masks when out in society. The role of masks in containing the spread of this and similar viruses cannot be overemphasised despite the politicisation of masks by politicians in the USA. The universal adoption of mask-wearing has been extremely useful in limiting the extent of the spread of the virus in Asia. Masks come in several different types, from the N95 masks which when well fitted have the highest degree of protection for the individual user, to surgical and cloth masks. The important thing to note is that using a mask of whatever type significantly cuts down on virus containing droplets leaving the mouth and nose of an infected person. The use of any kind of mask does offer some protection against inhaling virus particles but more importantly lowers the risk of an infected person (with or without symptoms) expelling the SARS-CoV-2 virus into the atmosphere. If universal mask-wearing can be achieved, this would pose a significant barrier to disease transmission in the community. Other practices thought to be useful include sneezing or coughing into the elbow as opposed to the hand, avoiding handshaking, frequent hand washing and avoiding touching your mask or face.

In conclusion, despite the controversies and paucity of randomised clinical trials, the overall message remains the same. To reduce personal risk of COVID-19 disease and community spread we should practice social distancing when out in the community, wear a mask in the presence of others, try to avoid crowded or poorly ventilated areas, frequently clean heavily trafficked public areas and wash our hands often with soap using good technique.

Hoping that you and yours remain safe.

Dr Ernest Madu, MD, FACC, and Dr Paul Edwards, MD, FACC are consultant cardiologists at the Heart Institute of the Caribbean (HIC) and HIC Heart Hospital. Correspondence to emadu@caribbeanheart.com or call 876-906-2107