Not More than 15min Exposure in 24 hours
The operational definition of “prolonged” refers to a cumulative time period of 15 or more minutes during a 24-hour period, which aligns with the time period used in the guidance for community exposures and contact tracing. Although this definition can be used to guide decisions about work restriction, appropriate follow-up, and contact tracing, the presence of extenuating factors (e.g., exposure in a confined space, performance of aerosol-generating procedure) could warrant more aggressive actions even if the cumulative duration is less than 15 minutes. For the purposes of this guidance, any duration should be considered prolonged if the exposure occurs during performance of an aerosol generating procedure.1
Footnote 1
1Data are insufficient to precisely define the duration of time that constitutes a prolonged exposure. Until more is known about transmission risks, it is reasonable to consider a cumulative exposure of 15 minutes or more during a 24-hour period as prolonged. This could refer to a single 15-minute exposure to one infected individual or several briefer exposures to one or more infected individuals adding up to at least 15 minutes during a 24-hour period. However, any duration should be considered prolonged if the exposure occurred during performance of an aerosol generating procedure.
https://www.cdc.gov/coronavirus/2019-ncov/hcp/guidance-risk-assesment-hcp.html
Explains the research results that led to this guideline.
https://www.statnews.com/2020/10/21/cumulative-time-covid-19-spread/
"During their interactions, the incarcerated people were wearing masks most, but not all, of the time, while the officer always had a microfiber cloth mask, gown, and eye protection on."
So, if everyone wears masks all the time, and we wear better masks than cloth mask, the duration can be more than 15 minutes, in enclosed spaces. Even longer in well ventilated spaces.
This is the actual report:
https://www.cdc.gov/mmwr/volumes/69/wr/mm6943e1.htm
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