| Study |  | Exclusion reasons | Remarks | Reference(s) |  | 
            
            
                | Loeb, 2004 | case control |  | Case-control study | Loeb  Emerging Infect. Dis. 2004; 10:251-5 10.3201/eid1002.030838 |  | 
            
            
                | Zhang, 2017 | case control |  | Case-control study | Zhang  Nursing Practice and Research. 2017;14:118-119. 10.3969/j.issn.1672-9676.2017.22.046 |  | 
            
            
                | Wilder-Smith, 2005 | case control |  | Case-control study | Wilder-Smith  Emerging Infect. Dis. 2005; 11:1142-5 10.3201/eid1107.041165 |  | 
            
            
                | Ma, 2004 | case control |  | Case-control study | Ma  Zhonghua Liu Xing Bing Xue Za Zhi 2004; 25:741-4  |  | 
            
            
                | Wang, 2020 | case control |  | Case-control study | Wang  JAMA 2020; : 10.1001/jama.2020.1585 |  | 
            
            
                | Yin, 2004 | case control |  | Case-control study | Yin  Zhonghua Liu Xing Bing Xue Za Zhi 2004; 25:18-22  |  | 
            
            
                | Cheng, 2010 | case control |  | Case-control study | Cheng  J. Hosp. Infect. 2010; 74:271-7 10.1016/j.jhin.2009.09.009 |  | 
            
            
                | Zhang, 2013 | retrospective cohort |  | Retrospective study | Zhang  Influenza Other Respir Viruses 2013; 7:466-71 10.1111/irv.12025 |  | 
            
            
                | Jaeger, 2011 | cohort |  | Cohort study | Jaeger  Infect Control Hosp Epidemiol 2011; 32:1149-57 10.1086/662709 |  | 
            
            
                | Nishiura, 2005 | case control |  | Case-control study | Nishiura  Am. J. Trop. Med. Hyg. 2005; 73:17-25  |  | 
            
            
                | Chokephaibulkit, 2012 | case control |  | Case-control study | Chokephaibulkit  Influenza Other Respir Viruses 2013; 7:359-63 10.1111/irv.12016 |  | 
            
            
                | Teleman, 2004 | case control |  | Case-control study | Teleman  Epidemiol. Infect. 2004; 132:797-803 10.1017/s0950268804002766 |  | 
            
            
                | Zhang, 2012 | case control |  | Case-control study | Zhang  Emerging Infect. Dis. 2013; 19: 10.3201/eid1909.121765 |  | 
            
            
                | Wu, 2004 | case control |  | Case-control study | Wu  Emerging Infect. Dis. 2004; 10:210-6 10.3201/eid1002.030730 |  | 
            
            
                | Sung, 2016 | retrospective cohort |  | Retrospective study | Sung  Clin. Infect. Dis. 2016; 63:999-1006 10.1093/cid/ciw451 |  |