BackgroundCommercial flights contributed to the early-stage international transmission of severe acute respiratorysyndrome coronavirus 2 (SARS-CoV-2). Understand the effect of international and inter-state flights on thevirus transmission is important to evaluate the initial response of the outbreak. This study investigated thelikely date of the emergence of the first COVID-19 case in Wuhan, China.MethodsWe constructed a geographical-structured model, including 9122 county-level geographical units in 250different regions or countries, and 26,094,036 flight plans. Using the model, we estimated the date of thenumber of deaths and the date of first death caused by COVID-19 in 155 different countries. We set acertain trigger for country and county level lockdown, and a built-in flight randomizer, to assess thedifferent evidence that can suggest the possibility of different dates to be the emergence of the firstCOVID-19 case.FindingsWe found the median number of global deaths caused by COVID-19 from 50 trails of our simulation isbetween 853901 and 28432 when the emergence of the first case of COVID-19 case is within the timeinterval between September 1, 2019 and November 1, 2020. Overall, the average and median R2 of 155countries decrease as the date of the emergence postpone; however, a small increase of R2 is observed whenthe date emergence of the first case of COVID-19 case is September 22. The deviation of the simulationresult of the deaths from the actual scenario in the eight major epicenters demonstrates a negative trend asthe first case emerges later. A similar pattern can be observed on the date of the first death in these eightcountries, which can be applied to a global scale.InterpretationsWe found that our simulation results can only include the actual number of global deaths caused byCOVID-19 on May 1,2020 inside the 95%PI when the date of the emergence of the first case is betweenSeptember 15, 2019 and October 15, 2020; The lowest deviation can be observed on September 22. Wealso found a decrease of R2 when we deploy later emergence of the first case; unexpectedly, an abnormalincrease of R2 on September 22 is observed. When focusing on the eight major epicenters, we found that thenumber of deaths in these eight countries can only be all included inside the 95%PI when the emergence ison September 15 and September 22. The deviation of the first deaths demonstrates different patternsdepending on the continent, whereas the global average demonstrates a pattern of normal distribution witha maximum of 0.2107 on September 22 after the removal of outliers. This could suggest a high likelihoodof the emergence of the first case of COVID-19 be around September 15, 2020 and September 22, 2020.
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