An evolutionary analysis based on the genome sequences of COVID-19 coronavirus samples taken from patients in the Seattle area suggests that the number of infections doubles roughly every six days, which translates into hundreds of infections over the course of the past six weeks.
So far, 18 cases have been confirmed in Western Washington, including 14 in King County and four in Snohomish County, north of Seattle. As of today, five patients have died — four in King County and one in Snohomish County.
But the analysis laid out in a series of tweets from Trevor Bedford, a researcher at Seattle’s Fred Hutchinson Cancer Research Center who specializes in the study of viral dynamics, concludes that many more people are likely to be part of a chain of infections leading from the first patient in the U.S. to be diagnosed with the virus. Some probably passed along the virus even though they didn’t know they were infected — a phenomenon known as “cryptic transmission.”