Objectives We aim to describe the fraction of asymptomatic health-care workers (HCWs) in two designated hospitals for COVID-19 treatment in Wuhan and explore the factors associated with asymptomatic SARS-CoV-2 infection. Methods All HCWs in Wuhan Union Hospital and Wuhan Red Cross Hospital with either positive SARS-CoV-2 nucleic acid or antibody test before April 18, 2020 were included. Exposure, epidemiologic, demographic information were retrospectively collected by a structured questionnaire. Medical records were also reviewed for clinical characteristics and CT images in HCWs. Results As of April 18, 2020, a total of 424 HCWs were identified. Among them, 276 (65.1%) were symptomatic and 148 (34.9%) were asymptomatic. 55 (19.9%) families of the symptomatic HCWs and 16 (10.8%) families of the asymptomatic HCWs were infected with SARS-CoV-2. HCWs with infected family members tend to be symptomatic cases (Odds ratio [OR], 2.053 [95% confidence interval (CI), 1.130-3.730]; P=0.018). Multivariable logistic regression analysis exhibited that performing tracheal intubation or extubation (OR, 4.057 [95% CI, 1.183-13.909]; P=0.026) was associated with an increased likelihood of symptomatic SARS-CoV-2 infection, while consistent use of N95 respirators (OR, 0.369 [95% CI, 0.201-0.680]; P=0.001) and eye protection (OR, 0.217 [95% CI, 0.116-0.404]; P<0.001) were associated with an increased likelihood of asymptomatic SARS-CoV-2 infection. Conclusions Asymptomatic SARS-CoV-2 infection in HCWs occupies a considerable proportion during the pandemic of COVID-19. Those who have performed tracheal intubation or extubation were most likely to develop related symptoms, while those taking aggressive measures including consistent use of N95 masks, and eye protection tended to be asymptomatic cases.

Summary Here, we describe a protocol for CRISPR/Cas9-mediated gene knockout in conditionally immortalized immature dendritic cells (DCs), which can be limitlessly expanded before differentiation. This facilitates the genetic screening of DC functions in vitro including assessment of phagocytosis, cytokine production, expression of co-stimulatory or co-inhibitory molecules, and antigen presentation, as well as evaluation of the capacity to elicit anticancer immune responses in vivo . Altogether, these approaches described in this protocol allow investigators to link the genotype of DCs to their phenotype. For complete details on the use and execution of this protocol, please refer to Le Naour et al. (2020) .