Risk factors for disease progression in patients with mild to moderate coronavirus disease 2019—a multi-centre observational study - Y.-Y. Cen; Xi Chen; Yuning Shen; Xiaohong Zhang; Lei Yang; Cheng Xu; Wen-Rong Jiang; Hongtao Xu; Yuchen Chen; Jie Zhu; L.-L. Zhang; Yuhui Liu (2020)