Table 2. Attack rates of COVID-19 in contacts with different characteristics.

Characteristics	Total contacts	Total infections	Attack Rate (%)
Age of contacts (years)
0–9	1048	60	5.7
10–19	819	33	4.0
20–29	2420	56	2.3
30–39	2601	113	4.4
40–49	1878	56	3.0
50–59	1520	76	5.0
60–69	831	92	11.1
70–79	314	21	6.7
≥80	149	7	4.7
Sex
Male	6183	213	3.4
Female	5397	302	5.6
Relationship to the index case
Spouse	563	131	23.3
Family members (non-spouse)	1878	199	10.6
Close relatives	1341	94	7.0
Other relatives	925	38	4.1
Social activity contacts	3344	41	1.3
Transportation contacts	2778	10	0.3
Health care workers	573	2	0.3
Others	178	0	0.0
Contacts on different transportations
Flight	695	6	0.8
Train	901	11	1.2
Public transportation*	229	5	2.1
Private car	213	9	4.2
The Dream Cruises	63	6	9.5
Unknown	1104	14	1.3
*Indicate other public transportations mainly including bus, taxi, subway, ferry, etc.
Disease history of confirmed index cases#
Incubation period	2211	72	3.3
Symptomatic period	5904	411	7.0
Contacts to the index cases at different time (days to the symptom onset)*
≤−5	522	9	1.7
−4 to −3	283	6	2.1
−2 to −1	974	25	2.5
0	1020	61	5.6
1–2	1036	81	7.3
3–4	865	97	10.1
5–6	702	61	8.0
7–8	371	31	7.7
9–10	223	16	6.7
11–12	106	6	5.4
13–14	109	4	3.5
15–16	188	10	5.1
≥17	265	11	4.0
Clinical severity of index case
Mild	1244	57	4.6
Moderate	5637	344	6.1
Severe	812	52	6.4
Critically severe	371	28	7.5

*Minus number indicates days before the symptom onset, plus number indicates the days after the symptom onset in confirmed cases, and zero indicates the day of symptom onset. In order to precisely estimate the contacting time, only the pairs with only one index case and one secondary case were included.