Table 1.

Characteristic of included studies.

Study	Country	Study design	Sample	Age	Gender (M/F)	Symptomatic cases	Asymptomatic controls	Severe cases	Non-severe controls	Died cases	Alive controls	NOS
Zeng et al. (2020)	China	Retrospective	234	>13	133/101	0	0	97	137	21	76	6
Zhao et al. (2020)	China	Retrospective	5469	NR	NR	1775	3694	0	0	206	1569	8
Zhao et al. (2020)	China	Retrospective	3807	NR	NR	113	3694	0	0	0	0	8
Zhao et al. (2020)	China	Retrospective	23,671	NR	NR	285	23,386	0	0	0	0	8
Zietz and Tatonetti (2020)	Columbia	Retrospective	1559	NR	716/843	682	877	179	423	80	602	8
Xiang et al. (2020)	China	Retrospective	54	18–78	33/16	0	0	5	49	0	0	6

M/F:male/female.

NOS: Newcastle–Ottawa Scale.

NR: Not reported.