. 2021 May 11;117:372–377. doi: 10.1016/j.ijid.2021.04.064

Table 2.

The secondary attack rate and severity category of cluster infection of COVID-19.

Variables		Transmission generations, n (%)				P-value
	Total	Index case	1^st generation	2^nd generation	3^rd generation
Secondary attack rate						＜0.001
Confirmed and asymptomatic cases	149	91	50	8	0
Number of close contacts	3186	1282	1004	792	108
Secondary attack rate	4.7	7.1	5.0	1.0	0.0
Clinical category						0.008
Mild	37(15.1)	11(29.7)	19(51.4)	5(13.1)	2(5.4)
Moderate	168(68.6)	64(38.1)	62(36.9)	38(22.6)	4(2.4)
Severe	20(8.2)	13(65.0)	7(35.0)	0(0.0)	0(0.0)
Critical	1(0.4)	1(100.0)	0(0.0)	0(0.0)	0(0.0)