“…A total of 6,609 possibly relevant articles were identified in PubMed and EMBASE database by our search strategy and manual searching; no relevant article published in Chinese was identified in CNKI database. As shown in Figure 1, 23 observational studies (Arsic Arsenijevic et al, 2014;Blaecher et al, 2013;Bu et al, 2015;Charlett et al, 1999Charlett et al, , 2009Dobbs, Charlett, Dobbs, Weller, & Peterson, 2000;Golabi et al, 2017;Goldstein, Fogel-Grinvald, & Steiner, 2019;Harris et al, 2012;Hemling et al, 2003;Huang et al, 2018;Kim et al, 2016;Nafisah et al, 2013;Nielsen, Qiu, Friis, Wermuth, & Ritz, 2012;Pakpoor et al, 2017;Sasco & Paffenbarger, 1985;Su et al, 2019;Tanner et al, 2012;Toovey, Jick, & Meier, 2011;Tsai et al, 2016;Tsolaki, Kountouras, Topouzis, & Tsolaki, 2015;Vlajinac et al, 2013;Wu et al, 2015) including six retrospective cohort study and 17 case-control studies published from 1965 to 2019 were included. Among these 23 studies, infection of 21 pathogenic microorganisms including eight bacteria, 12 viruses and one fungus were reported (Table 1).…”