INS and diabetes mellitus: They performed a retrospective study involving 904 patients with DM and COVID-19 and confirmed that insulin users had a greater risk of poor prognosis compared with noninsulin users (aOR 3.58 [95% CI 1.37, 9.35]; p = 0.009), but the study could not rule out the possible existence of truly uninfected patients among the clinically diagnosed cases (Chen et al., 2020).