On 2020-03-08 a superspreading event most likely occurred in Washington. 15 days later (2020-03-23) it started to super-spread through the community. A total of 66 copies of this genome (that represents the core of the outbreak), were reported in Gisaid, a proxy for primary transmissions, along with 266 genomes that are one-step mutation with respect to the core genome (a proxy for secondary transmissions). The signature for the likely superspreading event ends at about 2020-03-31, 22 days after it started, with 4313 sequences found in total.
The last sequence of the superspreading event was collected on 2020-06-29.