Abstract
Previously, we demonstrated a strong correlation between the amplitude of human speech and the emission rate of micron-scale expiratory aerosol particles, which are believed to play a role in respiratory disease transmission. To further those findings, here we systematically investigate the effect of different 'phones' (the basic sound units of speech) on the emission of particles from the human respiratory tract during speech. We measured the respiratory particle emission rates of 56 healthy human volunteers voicing specific phones, both in isolation and in the context of a standard spoken text. We found that certain phones are associated with significantly higher particle production; for example, the vowel /i/ ("need," "sea") produces more particles than /ɑ/ ("saw," "hot") or /u/ ("blue," "mood"), while disyllabic words including voiced plosive consonants (e.g., /d/, /b/, /g/) yield more particles than words with voiceless fricatives (e.g., /s/, /h/, /f/). These trends for discrete phones and words were corroborated by the time-resolved particle emission rates as volunteers read aloud from a standard text passage that incorporates a broad range of the phones present in spoken English. Our measurements showed that particle emission rates were positively correlated with the vowel content of a phrase; conversely, particle emission decreased during phrases with a high fraction of voiceless fricatives. Our particle emission data is broadly consistent with prior measurements of the egressive airflow rate associated with the vocalization of various phones that differ in voicing and articulation. These results suggest that airborne transmission of respiratory pathogens via speech aerosol particles could be modulated by specific phonetic characteristics of the language spoken by a given human population, along with other, more frequently considered epidemiological variables.
Highlights
Airborne disease transmission between humans is believed to result from the release of infectious microorganisms into the air from an infected individual via expiratory activities, and their subsequent inhalation by a nearby susceptible person [1,2,3,4,5,6,7]
Our particle emission data is broadly consistent with prior measurements of the egressive airflow rate associated with the vocalization of various phones that differ in voicing and articulation. These results suggest that airborne transmission of respiratory pathogens via speech aerosol particles could be modulated by specific phonetic characteristics of the language spoken by a given human population, along with other, more frequently considered epidemiological variables
We found no statistically significant difference in overall aerosol particle emissions for any of the four languages; the distribution of phones in the translated texts was neither measured nor controlled, so it remains unknown if specific elements of speech, which may be more common in one language than another, are associated with increased particle emission
Summary
Airborne disease transmission between humans is believed to result from the release of infectious microorganisms into the air from an infected individual via expiratory activities (e.g. sneezing, coughing, talking, and breathing), and their subsequent inhalation by a nearby susceptible person [1,2,3,4,5,6,7]. Yan et al [9] detected infectious influenza virus in 39% of fine aerosol samples collected from human volunteers with influenza during 30 minutes of normal tidal breathing and occasional prompted speech. Their data further confirmed that sneezing and coughing are not necessary for the aerosolization of viable influenza virus [9]
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