Table 1. Time from symptom onset to diagnosis confirmed and from admission to reaching sever level.

Time	N	Mean	Standard deviation	Min	1st Qu.	Median	3rd Qu.
From symptom onset to diagnosis confirmed	905	6.97	5.33	0	3	6	9
From symptom onset to first medical visit	1,385	3.67	4.12	0	0	3	6
From first medical visit to diagnosis confirmed	882	3.73	5.03	0	1	2	5
From admission to reaching sever level	1,240	9.34	5.94	0	7	8	11

In this cohort, 1,590 cases in total, there are 1,501 cases with symptom onset date, 1,512 cases with first medical visit date, 935 cases with diagnosis confirmation date, 1,246 cases with admission date, 234 cases developed to severe level and with the exact date. The missing data in 4 kinds of time length above met the assumption for Missing Completely at Random (MCAR), and no method of replacement was used, according to logit statistics method considering age, pre-existing diseases, and endpoint factors.