Effect of speech volume on respiratory emission of oral bacteria as a potential indicator of pathogen transmissibility risk.

Respiratory droplets emitted during speech can transmit oral bacteria and infectious viruses to others, including COVID-19. Loud speech can generate significantly higher numbers of potentially infectious respiratory droplets. This study assessed the effect of speech volume on respiratory emission of oral bacteria as an indicator of potential pathogen transmission risk. Loud speech (average 83 dBA, peak 94 dBA) caused significantly higher emission of oral bacteria (p = 0.004 compared to no speech) within 1 ft from the speaker. N99 respirators and simple cloth masks both significantly reduced emission of oral bacteria. This study demonstrates that loud speech without face coverings increases emission of respiratory droplets that carry oral bacteria and may also carry other pathogens such as COVID-19.