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Exploring how speech air flow may impact the spread of airborne diseases: Q&A with Dr. Donald Derrick

February 1, 2022

The COVID-19 pandemic has made research into virus transmission a top scientific priority. SARS-CoV-2, the virus that causes COVID-19, can be spread through virus-infected saliva droplets and particles. The details of how far and fast saliva droplets and particles disperse through the air, and under what circumstances, remain under investigation.

Dr. Donald Derrick, Senior Lecturer at the University of Canterbury and Language Sciences member, discusses his research surrounding the spread of airborne diseases and viral load leading up to the American Association for the Advancement of Science's (AAAS) panel, 'Transmission of Airborne Pathogens through Expiratory Activities' happening at the AAAS Annual Meeting on February. 18, 2022. Learn more about the panel here.

What does your current research focus on?

I work on many projects and many fields including: 1) Phonetic research on endangered (Iwaidja, Blackfoot) and other (English, Mandarin, Emirati Arabic) languages; 2) Evolutionary research: Showing that the tongue can switch gait-like motion patterns between slow and fast speech - like the switch from walking to running; 3) Community health: Where we demonstrated benefits of sex education and nutrition planning on birth weights of babies born in Burmese migrant camps in Thailand; and 4) LInguistics and Music: Where we demonstrated that native language influences how you hold your tongue during trombone playing.

However, you are probably most interested in my research that focuses on multimodal speech production and multisensory perception. In this research on speech air flow, we demonstrated that speech air flow contacting a perceiver’s skin influences their perception of syllables and words. This research also led us to study how speech air flow moves out of the mouth and nose of people without face-masks, and people wearing all sorts of face masks. This research just came out in Scientific Reports.

This research shows all of the face masks reduced air flow from speech, but some allowed air flow features to reach further than 40 cm from a speaker’s lips and nose within a few seconds, and all the face masks allowed some air to escape above the nose. There is a tradeoff between highly porous masks that stop most top, bottom, and side leakage but allow air to flow out the front, and masks that tend to have a worse fit on the edges and so let air out there. A tight N95/KN95 mask can help, as can a metal strip built into the mask at the nose, but all masks will leak some air. 

While we did not study the spread of infectious particles so much as air motion, our results do pattern well with research that shows masks provide the most benefit in medium-risk environments. It is hard to get an airborne disease outdoors or in a highly well ventilated area, so masks don’t matter so much there. It is impossible to avoid getting airborne diseases in the middle of a flu ward if you stay there day after day - unless you up the standard beyond just surgical or N95 masks. However, you can reduce risk of spreading disease by wearing masks at supermarkets or while walking through malls for relatively short periods of time.

What is something that people may not be aware of relating to human airflow and the spread of droplets and aerosols?

Two things: 1) The air flow from one speech sound can pass right through the air flow from a previous speech sound because speech sounds vary quite a bit in their ability to move air and penetrate into the environment. Nevertheless, speech air flow does not travel nearly as far as speech sound. 2) When we model risk of infection, we make many assumptions about viral load and the amount, or quanta, of virion particles needed to have, say, a 66.7% chance of infecting someone. These assumptions need to be regularly updated because different diseases and different variants have very different risk factors.

Can you share a small taste of what people might expect to learn from you on the AAAS panel, ‘Transmission of Airborne Pathogens through Expiratory Activities’?

My video will be focused on the face mask research. However, it also presents evidence that it is incredibly hard to get COVID-19 outdoors when you socially distance 6 feet or more (at the time of writing the video, there had been no documented cases at all). It will also show how hospitals that have negative pressure rooms actually can set up environments where N95 masks then do protect medical professionals, contra to what I said above (which itself was based on a massive study of Ontario Nurses and their rates of contracting the flu).

Learn more about AAAS and click here to register to attend the 2022 AAAS Annual Meeting.

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