Expansion of droplets during speaking and singing in Japanese.

During the COVID-19 pandemic, a number of infection clusters associated with choral singing have been reported. Singing generates droplets and carries the risk of spreading infection. However, no reports have explored droplet flight and aerosol production rates by singing and speaking in Japanese. First, we conducted an observation experiment evaluating the maximum flight distance and number of droplets generated by singing in Japanese, using a high-speed camera and particle counter. Twenty amateur choir members, 10 male and 10 female (five members for each of the four voices), participated in the experiment. Subsequently, although the maximum distance that droplets traveled by singing in Japanese was 61 cm for men (median of 46.5, interquartile range, 36-57) and 56 cm for women (median of 27.5, interquartile range, 20-50), droplets were observed anteriorly and laterally to be up to 66.8 cm. At the singer's mouth, ≥ 5 μm droplets were observed, whereas not observed at 1 meter toward the front of the singers in women and men, respectively. In German singing, droplets were observed up to 111 cm toward the front of the singer, possibly reflecting differences in pronunciation. In Japanese reading aloud, droplets were also observed up to 47 cm toward the front, whereas no droplet dispersion was observed by speaking the Japanese /a/ vowel or singing with wearing surgical mask toward the front. The aerosols produced when reading singing the /u/ vowels were significantly higher than those in other vowels. When singing in a choral group, keeping a sufficient distance at the front and side is recommended in minimizing infectious spread. If distance is not possible, practicing with /a/ vowels and avoiding consonants may be an alternative method. Our observations lasted only 50 seconds per song, and further observational studies are needed to determine the dynamics of aerosols that stay for long periods.