A study by Kazahiro Tateda MD, PhD, professor of microbiology and infectious disease at Toho University, Tokyo, and NHK, Japan’s national broadcasting organisation, suggests that viruses, including the COVID-19 coronavirus, may be spread by microdroplets released in conversation. With microdroplets remaining airborne for 20 minutes or more in stagnant air, maintaining social distance, wearing masks and occasionally opening the window may help mitigate the infection risk they present.
The study used high-speed cameras to examine droplets dispersed when people sneezed, coughed, spoke and breathed. It showed that large droplets expelled by coughing and sneezing settled to the ground rapidly, suggesting they are a temporary inhalation threat. Touching such drops, which measure up to 1.0mm in diameter, after they settle, and then touching the face is thought to be their most common route transmitting disease.
However, microdroplets dispersed by talking loudly or breathing heavily not only remained suspended for minutes or hours in the air. They also tended to accumulate in enclosed spaces with poor ventilation. Measuring just a few microns, such microdroplets are still capable of carrying and possibly spreading viruses by inhalation.
Creating a cross draft by opening two windows appeared highly effective in clearing the air of suspended microdroplets, said Dr Tateda, who is president of the Japanese Association for Infectious Disease, which partnered in the study. He recommended opening windows periodically to keep microdroplets from accumulating.
The study has not been published in a peer reviewed journal, but a report on it has been broadcast on NHK World, and can be viewed here.
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