It is well known that respiratory droplets have a key role to play in the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus. The virus is transmitted through direct, indirect, or close contact with an infected personby means ofthe infected secretions from the patient, including saliva and respiratory droplets, which may be expelled during coughing, sneezing or talking.Airborne transmission has also been reported under certain circumstances, especially during aerosol generating procedures.¹

Therefore, it becomes important that we understand the role of air that is expelled during coughing or sneezing, and its mixing with the air in a given environment, in transmission of the COVID virus.

Coughing creates a jet-like flow and when an infected person coughs, it goes on to contaminate a large volume of air in the immediate vicinity of the person. Researchers at the Indian Institute of Technology Bombay sought to estimate this volume of air in their recent study.² It is known that the velocity in a cough cloud dwindles with distance (Phys. Fluids 32, 081905 (2020)).

The researchers further evaluated the data to determine the volume of the cough cloud in the presence as well as absence of a face mask.

The findings –

• The volume of the cough cloud without a mask was nearly 7-fold greater than in the presence of a surgical mask; 23-fold greater than when an N95 mask was used.
• The cough cloud persisted for 5 to 8 s.
• The cough cloud reached room temperature, and remained slightly more moist compared to the surrounding.

To sum up

• The initial 5 to 8 s are vital after the cough event.
• When a mask is used, the volume of air expelled in the cough cloud is reduced considerably, thus minimizing the risk of transmission to other people in the enclosed space.
• The type of mask used is also important.

References

1. Transmission of SARS-CoV-2: implications for infection prevention precautions. Available from: https://www.who.int/news-room/commentaries/detail/transmission-of-sars-cov-2-implications-for-infection-prevention-precautions.  Accessed on February 11, 2021.
2. Agrawal A, Bhardwaj R. Reducing chances of COVID-19 infection by a cough cloud in a closed space. Physics of Fluids 32, 101704 (2020).