It’s generally agreed that avoiding exposure to the deadly Covid-19 virus, officially named SARS-CoV-2, is achieved through physical distancing and also basic hygiene, which entails frequent, thorough handwashing, and avoiding contact with surfaces that are touched by a lot of people, such as doorknobs and elevator buttons.
However, with the constant emergence of new studies, we are learning of other ways in which the virus can be transmitted, particularly via aerosol (small respirable particles that can remain airborne, and travel short and long distances) transmission.
A recent study, undertaken by four researchers and published in Risk Analysis, provides evidence for aerosol transmission of the virus. This was done by studying how the normal breathing and talking of asymptomatic individuals produce small droplets that can travel through the air.
What the study says
Physical distancing measures across the world, including the implementation of lockdowns as well as the mandatory wearing of face masks, has been prompted by the fact that SARS-CoV-2 spreads through two main avenues: coughing and sneezing from infected individuals, and through hand-to-face transport from surfaces.
Although not everything is known about airborne aerosol transmission of the new coronavirus, the researchers explain that the difference between small and large droplets in infectious disease transmission (originally observed in the 1930s) is reflected in current World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC) guidance, as well as additional publications.
A news release by EurekAlert also notes that a letter in April by the National Academy of Sciences Committee on Emerging Infectious Diseases and 21st Century Health Threats concluded that, despite limited research on SARS-CoV-2 specifically, "the results of available studies are consistent with aerosolisation of virus from normal breathing".
The researchers of this study, therefore, aim to draw more attention to the inhalation of aerosols. They describe that reports of asymptomatic (symptom-free) individuals infecting others with Covid-19 show that normal breathing and talking can end up producing tiny droplets, which can then be transported. And, since the droplets are really small, they have the ability to linger in the air for long periods of time, which is what allows them to travel greater distances.
Eurekalert also reports that a recent laboratory study discovered that the virus can remain viable and infectious in aerosols for hours, and on surfaces for days. Similarly, a HealthDay article, published in April, reports on studies that discovered that people infected with the virus could spread aerosolised viral particles as they cough, breathe or talk in a 13ft (4m) radius. Other interesting studies, reported by Health24, reveal how the virus can remain on plastic for 72 hours and on cardboard for 24 hours. Another more recent study published by Health24 found that chances of infection via aerosol transmission increase in poorly-ventilated areas.
What the authors suggest
The authors offer certain recommendations to address aerosol transport of the virus, including collecting more data exploring the concentration, duration of survival, and the transport distances for the virus in its aerosol form. They recommend that scientists do this during a variety of temperatures and humidity levels.
Another suggestion they put forward is to explore appropriate ways of curbing inhalation exposure to small aerosols, specifically within buildings and rooms where the aerosols are likely to travel and settle.
As of 13 April, there were a total of just over 4.2 million confirmed cases and more than 290 000 reported deaths worldwide, indicated by the Johns Hopkins Coronavirus Resource Center.
Image: Priscilla Du Preez on Unsplash