In late February 2020, an outbreak of SARS-CoV-2 occurred at a long-term care skilled nursing facility (SNF) in King County, Washington. On March 1, a healthcare provider tested positive for SARS-CoV-2 after working while symptomatic on February 26 and 28. Seven residents of the second facility were symptomatic with positive test results by March 6, 2020. 93% of facility A residents were tested and screened as symptomatic or asymptomatic at time of testing. Among 23 residents who tested positive, 10 (43%) were symptomatic and 13 (57%) were asymptomatic. Seven days later, 10 of the 13 previously asymptomatic had developed symptoms and were re-categorized as "presymptomatic". Large quantities of RNA in all cases indicated transmission potential regardless of symptoms.

Asymptomatic and Presymptomatic SARS-CoV-2 Infections in Residents of a Long-Term Care Skilled Nursing Facility - King County, Washington, March 2020

Perhaps one of the most known instances of asymptomatic or presymptomatic transmission through aerosol in the USA was the Skagit Valley Chorale rehearsal in Mount Vernon, Washington. Although interview revealed that the attendees were not symptomatic and were minimizing contact by keeping their distance, 45 out of the 60 attendees were later tested positive for the virus after the rehearsal. Out of the 45 people, three were hospitalized, and two of them have died.

Transmission in the Skagit Valley Chorale

University of Michigan - Ann Arbor

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