On 2020-03-09 a superspreading event most likely occurred in Michigan. 5 days later (2020-03-14) it started to super-spread through the community. A total of 115 copies of this genome (that represents the core of the outbreak), were reported in Gisaid, a proxy for primary transmissions, along with 191 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 2020-03-30, 20 days after it started, with 2503 sequences found in total.
The last sequence of the superspreading event was collected on 2020-11-07.