By Dr. Zulfikar Bux
Assistant Professor of Emergency Medicine, Vanderbilt Medical Center

DATA is now emerging to help us to zone in on hotspots for COVID-19 transmission so that we may be able to manoeuvre around them and sustain our livelihoods. The most convincing data thus far are from two studies which showed high transmission rates of the virus indoors and very limited transmission in the outdoor setting where free flowing air dispersed virus particles quickly.

The first study was carried out in Denmark where 3,030 participants were studied while the other study was done among 1,848 U.S Marine recruits in South Carolina. Experts concluded from these studies that COVID-19 transmission was predominantly indoors and even occurred in those that were wearing standard surgical/cloth masks. They found that the “4 Ds” were the main risk factors that predicted COVID-19 transmission in the indoor setting. Today, I will expand on the 4Ds and why you should avoid such settings if you want to avoid COVID-19.

Density
Density meaning the number of people in a room was a major factor in predicting COVID-19 spread. The basic idea was that the more persons you have in a closed space, the likelier COVID-19 would spread if one or more persons had the infection. Viral particles will be expelled from the infected person’s mouth and nostrils and will “hang around” in the air longer because of poor air circulation in a closed space. With everyone breathing, the odds become higher of breathing in air with viral particles given the limited air to person ratio.

Duration
The longer one spends in a closed space with someone that is infected, the likelier one will become infected even if one is wearing standard surgical/cloth masks. An infected person in a closed space will expel more viral particles into the air every time he/she breathes, sneezes, coughs or speaks. It is obvious that the longer someone spends in such an environment, the higher the chance of him/her being exposed to expelled viral particles because he/she will be exposed to a higher concentration with time. Also, think about being in a room where the virus is moving around; the longer you spend in that room, the likelier the chances of you coming into contact with it as it moves around.

Dimensions
The smaller the dimensions of a closed space, the higher the chance of getting infected. As an infected person expels virus particles into the air, it will disperse faster once there is sufficient space for it to move into. However, in smaller spaces, the virus particles become stagnated and will circulate in that space for some amount of time. It is therefore obvious that one’s chances of coming into contact with viral particles will be higher when one is in a smaller, closed space.

Draft
In closed spaces where there is limited entry of fresh air and poor airflow speed, chances of COVID-19 transmission become higher. When viral particles get expelled into the air, they will remain floating for a while if the air is stagnant. However, if there is free flow of fresh air or air is mechanically propelled by fans, the viral particles will quickly disperse and not float around and infect persons that come into contact with it.
Offices, Restaurants, homes, Bars, Gyms, Cinemas etc. are examples of closed spaces where the risk of transmission will be higher. Therefore, it is obvious that we should minimize our presence with others in these and other indoor spaces as much as possible. If we have no choice, then ensure that these spaces are large, with minimal occupation and has free flowing air and we should minimize the time we spend in them when possible. While infections still occur with standard mask use in these spaces, it is far lesser and masks will help minimize severe infection risk by decreasing the amount of virus that gets into you. So, we should continue to practise mask wearing but change our lifestyle to ensure we avoid the 4Ds as much as we can, and carry out our exposures with others in the outdoor setting as much as possible.