Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes the novel coronavirus disease 2019 (COVID-19), was first identified in Wuhan, China, with notification to the World Health Organization on 31 December 2019, about a cluster of pneumonia cases of unknown etiology and release of the genomic sequence on 10 January 2020 . Subsequent reports have identified a patient with confirmed SARS-CoV-2 hospitalized in Wuhan with symptom onset as early as 1 December 2019 . In the United States, the first COVID-19 infection was reported on 19 January 2020 in a returned traveler from China, 2 days after domestic testing was initiated . While the first confirmed case had a symptom-onset date of 19 January 2020, 2 others within the first 12 US cases identified had illness-onset dates of 14 January 2020 . Some reports have suggested the introduction of SARS-CoV-2 into the United States may have occurred earlier than initially recognized, although widespread community transmission was not likely until late February [5–7].Simulation models used to predict COVID-19 case burden, subsequent healthcare utilization, and fatalities are reliant on accurately assessing date(s) of introduction of a pathogen into susceptible populations .