Table 2.

Newcastle-Ottawa scale for quality assessment and risk of bias.

Study	Year	Case selection (maximum 4)	Comparability (maximum 2)	Exposure/outcome (maximum 3)	Total score
Badr et al [14]	2020	3	2	2	7
Westgren and Acharya [15]	2020	3	2	1	6
CDCa [16]	2020	4	2	2	8
Cheng et al [17]	2020	3	1	2	6
Collin et al [23]	2020	4	1	2	7
Ellington et al [7]	2020	3	2	3	7
Liu et al [24]	2020	3	1	2	6
Martinez-Portilla et al [25]	2020	3	1	2	6
Yin et al [26]	2020	3	2	2	7
Mohr-Sasson et al [27]	2020	3	1	1	5
Molteni et al [28]	2020	3	1	2	6
Oakes et al [18]	2020	3	2	2	7
Qiancheng et al [19]	2020	3	1	2	6
Wang et al [20]	2020	2	2	2	6
Wei et al [21]	2020	3	1	3	7
Xu et al [22]	2020	3	2	2	6
Zambrano et al [29]	2020	3	1	3	7

^aCDC: Centers for Disease Control and Prevention.