Before revision:  In this paper, we investigate this problem using the data from the cases with symptom-onset dates from January 19 to February 10, 2020 for 100 Chinese cities , and cases with confirmed dates from March 15 to April 25 for 1,005 U.S. counties.
After revision:  In this paper, we investigate this problem using the data from the cases with symptom-onset dates from January 19 to February 10, 2020 for 100 Chinese cities and COVID-19 daily confirmed cases for 1,005 U.S. counties.