It is helpful to be reminded of Voltaire’s admonition: “Don’t let the perfect be the enemy of the good”. This is quite worthy at Covid times when new researches find that wearing a face mask is desirable even when indoors. A new research found that speaking in indoor spaces without wearing a face mask poses the greatest risk of spreading SARS-CoV-2.
The research published in the Journal of Internal Medicine, last week, details how different sized respiratory droplets emitted while speaking have a range of sizes, and can carry different amounts of virus. The researcher’s notes that the most concerning droplets are those of intermediate size that remains suspended in air for minutes. They claim that these droplets can travel over a considerable distances by air currents.
In the study, the researchers said that if a carrier’s mask results in 25 per cent leakage of respiratory droplets, the risk that a bystander inhales particles from a masked carrier drops fourfold. If the exposed contact also wears a mask, with an estimated ingress filtering efficiency of 50%, the aggregate infection probability is reduced eight fold.
Though one can see spit droplets flying when people talk, there are thousands more, too small to be seen by the naked eye, said lead author Adriaan Bax (US National Institute of Diabetes and Digestive and Kidney Diseases).
He said that when water evaporated from such speech-generated, potentially virus-rich droplets float in the air for minutes, like smoke.
In their extensive study, they found that airborne transmission was not only the dominant pathway for transmitting COVID-19, but unmasked speech in confined spaces represents the activity that poses the greatest risk to others.
The researchers opined that mitigation strategies should emphasise the use of facemasks when speaking next to vaccination. Apart from this, one should also ensure adequate ventilation to flush out long-lived aerosols. On the other hand, the aerosols might accumulate in closed environments and enhance the risk of more serious lower respiratory tract infections.
Despite some countries relaxing the use of facemasks, it has become the most widely adopted measure to mitigate the spread of COVID 19 pandemic next to keeping physical distance. Masks are broadly divided into three categories: respirator masks, for example KN95, N95, N99 and FFP1-3; surgical masks; and generic cloth masks. Masks serve primarily two functions: limiting egress of potentially infectious respiratory droplets; and protection of the mask wearer by reducing ingress of virus-laden aerosol.
The study also notes video recordings to emphasise that a face cover as simple as a washcloth blocks emission of more than 98 per cent of speech-generated droplets. However, an obvious shortcoming of both surgical and generic masks is that a portion of expired air leaks around the mask with the accompanying droplets avoiding capture. The extent to which this happens depends on the fit of the mask, air resistance by the mask material and exhalation airflow. Double masking has been proposed as a solution to reduce such leakage.