Community and Close Contact Exposures Associated with COVID-19 Among Symptomatic Adults ≥18 Years in 11 Outpatient Health Care Facilities — United States, July 2020 – CDC

“In the 14 days before illness onset, 71% of case-patients and 74% of control participants reported always using cloth face coverings or other mask types when in public.” 

https://www.cdc.gov/mmwr/volumes/69/wr/pdfs/mm6936a5-H.pdf