Covid-19 Droplets and Aerosol Transmission: How do we protect others and ourselves?
A multipronged approach that adjusts as new evidence comes to light is required to tackle the spread of Covid-19. Humility to listen and be adaptable is now more important than ever.
The rapid increase in the spread and transmission rate of the virus SARS-CoV-2 (Covid-19), has led to a frenzied upsurge in general and social media coverage. This, in turn, has led to many conflicting reports related to the spread and transmission of Covid-19 within various environments.
Hourly, we are bombarded with newspaper articles and social media stories, which relay “factual” information from “reliable” sources. The public is confused! While we are cautioned to only rely on information provided by the Centre for Disease Control and Prevention (CDC) and the World Health Organisation (WHO), there have also been many reputable research papers that have recently been published, related to the transmission and spread of the virus.
Furthermore, infectious disease experts working on the frontline of Covid-19 control have released videos and reports. Peer-reviewed journal articles and expert information from infectious disease specialists are thus important resources, which must be considered in our quest to learn as much as we can about this virus currently ravaging our globe. Let us thus attempt to simplify and collate the recent information related to the transmission and longevity of Covid-19.
To date, Covid-19 is known to spread by short-range respiratory droplets and is hypothesised to spread by longer-range aerosol transmission. When we consider the nature of aerosols versus droplets, we must understand that size and behaviour matter. The virus particle size is approximately 50 to 200 nanometres (nm) in diameter. To put this into perspective, one nm is one-billionth of a metre. The human eye (regular vision), without any assistance (magnifying glasses or microscopes etc.), can see objects of approximately 20 micrometres (µm) in size.
Nanometre-sized objects, like the coronavirus, are thus a thousand times smaller. Droplets are normally larger than 20 micrometres (µm) in diameter and are usually produced when coughing or sneezing. They are heavy enough to succumb to gravity and usually travel no more than one to two metres. When an infected person releases these droplets, each droplet may contain many virus particles. To complicate matters, droplets may travel further distances depending on wind conditions. Airflow thus influences the travel distance of droplets.
However, irrespective of the distance, when these droplets fall onto various surfaces, inanimate objects that now “carry” the infectious virus particles, are called fomites. The infection is then indirectly spread when an uninfected person touches these fomites and proceeds to touch their face (mucous membranes of the eyes, nose and mouth).
We therefore must stress the importance of handwashing and hand hygiene. However, we do not advocate irresponsible wearing of gloves. Just before the nationwide lockdown commenced, I (Sehaam Khan) was at the airport travelling from Johannesburg to Cape Town. Almost every person I encountered, whether airport staff or traveller, was wearing a pair of latex gloves. Now, I have been in the laboratory environment long enough to recognise a pair of gloves that have been worn for an extended period – the glove sticks to your skin because your hands are perspiring. This to me indicated that people were not regularly changing their gloves.
I watched in awe and horror as one young woman put her gloved hand to her mouth to blow a kiss at a colleague. In her mind, I am sure, the gloves were offering a form of protection. I am willing to bet that wearing those gloves may even have been considered as a replacement for hand washing. IT DOES NOT. You need to change your gloves numerous times a day. In fact, it should be noted that almost every time you touch an object, you need to dispose of the worn gloves. This is similar to what one observes when visiting a doctor! For many, this is not possible. Soap, water and proper hand hygiene works.
Direct infection (person to person) may also occur by droplet infection, if we stand within range (one to two metres), from the respiratory tract of an infected individual (cough or sneeze), to the mucous membranes of the uninfected person. Moreover, aerosol particles, which are normally smaller than 10 µm in diameter, can travel for many metres (greater than two meters) in the air before they fall to the ground or onto a surface, and may be inhaled.
As a countermeasure, many Asian countries have strongly advocated for the wearing of facemasks. In contrast, the WHO has indicated that wearing a facemask is not advisable. We encourage wearing a facemask when in public spaces for the following reasons: a) even with proper and frequent hand hygiene, unless you are washing your hands after touching every single object, there may be a time when you (an uninfected person) could come into contact with a fomite and inadvertently touch your face; b) by wearing a facemask, direct infection can also be curtailed; c) comparing the transmissibility rate of the USA and some European countries (e.g. Italy) to South Korea, Japan and Taiwan, it is evident that wearing a mask in public areas (together with many other factors) has positively contributed to controlling the virus spread; d) a facemask decreases the spread of the virus by an infected person; and e) if it is in fact true that non-symptomatic infected people may transmit the virus, it is definitely advantageous to encourage the public to wear facemasks, to curtail spread and infection.
Recently, the Czech Republic took the radical step of mandating the wearing of nose and mouth coverings in public spaces. In contrast, the US Surgeon General and WHO have stated that wearing a mask is not effective in preventing the public from being infected, yet state that they require these masks for their health professionals.
Ultimately, we are of the opinion that a protective measure like a surgical facemask, in conjunction with social distancing and good hand hygiene, will lower the virus infection rate. We do, however, support the sentiment that should there be a shortage of facemasks, health professionals should take priority.
The University of Johannesburg plays an important role in the Fourth Industrial Revolution (4IR). In my (Saurabh Sinha) contact with our campus clinics, we have directly faced the shortage of masks. One of our Chinese partner institutions, Shandong University, has donated 2,000 facemasks for campus clinics and security staff. Supported by an open-source design, we have 3D-printed face shields. In a university environment, one can occasionally find overhead projector transparencies and these have been used for the shield cover. A number of innovations have come about as a result of Covid-19. Like many other measures, post the control of a pandemic, our hope is that innovative thinking will remain and also assist with economic rebound.
We further understand that health professionals are trained in wearing professional protective equipment like facemasks, thus the likelihood of them constantly fiddling with their masks, and in so doing touching their faces, is substantially lower. Can we thus not teach the public proper “facemask etiquette”, in the same way that we have educated the public on how to wash their hands correctly?
There is a lot to still learn about Covid-19. One peer-reviewed article talks about the spread of Covid-19 at patient lavatories and change-rooms in hospitals. This is due to contamination in change-rooms and through fomites in lavatories. Shared spaces, like lavatories are, however, common given the socioeconomic conditions of informal settlements in South Africa. Focusing on healthcare professionals, a recent peer-reviewed study conducted in Wuhan Province, China, investigated for the presence of Covid-19 within various areas in two hospitals, during the outbreak.
The authors divided the sampling locations into patient areas (where the Covid-19 patients had a physical presence), and medical staff areas (workplaces in the two hospitals exclusively accessed by the medical staff who had direct contact with the patients). Their results showed that the Covid-19 concentrations were high inside the patient mobile bathroom (aerosol; one hospital), excessively high in the rooms where protective apparel of healthcare professionals were removed (aerosol; seven locations – one hospital) and high on the floor of the intensive care units (deposits; two locations – one hospital).
Researchers in Singapore, who also detected high levels of the virus in bathrooms, confirmed this study. In both studies, rigorous sanitation processes (when implemented) and the surface sanitation of protective apparel drastically reduced the virus numbers to undetectable levels.
We think it is evident that in order to slow down the virus transmission rate, a multipronged approach is required. It is also evident that we must be willing to constantly consider new information, and if necessary, adjust our recommendations based on evidence and global successes, that use best practice. Humility to listen and be adaptable is now more important than ever. Cover your nose and mouth, wash your hands regularly, practice physical distancing, implement rigorous sanitation processes in hospitals (where infected numbers may be higher), or shared lavatory spaces, and surface sanitise personal protective clothing. DM
Sehaam Khan is Professor (Microbiology & Molecular Virology) and Executive Dean: Faculty of Health Sciences, University of Johannesburg. Saurabh Sinha is Professor (Electronic Engineering) and Deputy Vice-Chancellor: Research and Internationalisation, University of Johannesburg.
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