Stadnytskyi and colleagues explored the size of droplets created by speech using a highly sensitive laser system. They reported in PNAS that speaking resulted in the generation of a high number of medium-sized droplets (10- to 100-µm in diameter). Under the conditions of their experiment (27% humidity and 23° C) they reported that speech probably generates droplets that originate at a size of 12 to 21 µm in diameter and quickly dehydrate to an estimated diameter of 4 µm. The 4 µm-sized particles had a falling rate of only 0.06 cm·s −1 and remained airborne for 8 to 14 minutes. 1
As reported by Hamner and colleagues, on March 10, 2020, 61 persons attended a 2.5-hour choir practice. One choir member had symptoms of an upper respiratory infection that began on March 7. Eventually that choir member tested positive for SARS-CoV-2. Of the 60 remaining persons, 52 (86.7%) eventually developed an upper respiratory illness. In total, 33 cases of SARS-CoV-2 were confirmed by nucleic acid testing and 20 probable cases were diagnosed (these individuals declined testing). The choir attendees developed symptoms at a median of 3 days following the practice, with a range of 1 to 12 days. Three of the 53 ill people were hospitalized, and two died. 2
The Stadnytskyi study suggests that speech generates large respiratory droplets that dehydrate into very small droplets that may remain in the air for an extended period of time. If the SARS-CoV-2 virus were in the original large droplet, the rapid dehydration of the droplet would result in prolonged airborne presence of the virus and enhance its infectivity.
The Hamner study highlights the importance of vocalization and respiratory particles in transmitting the SARS-CoV-2 virus. For clinicians and patients, both studies support many recommendations to reduce viral transmission, including:
- all clinicians and patients need to wear face masks
- all clinicians and patients should avoid face-to-face contact if alternative approaches to communication are possible
- all clinicians and patients should avoid gathering in large groups or crowded public spaces and need to maintain physical distancing.
The COVID pandemic has dramatically changed how we practice medicine and socialize.