Epidemiological characteristics of 3 054 COVID-19 patients with mild symptoms/asymptomatic infection in makeshift hospitals of Shanghai in 2022

OBJECTIVE To analyze the epidemiological characteristics of Omicron subvariant BA.2 represented mild/asymptomatic COVID-19 cases in makeshift hospitals. METHODS The data of COVID-19 patients who were mild and asymptomatic admitted to Shanghai Shilong Road Temporary Capsule Hospital from Apr 8 to May 13, 2022 were retrospectively collected. The epidemiological history, general situation, length of stay, severe acute respiratory syndrome coronavirus 2（SARS-COV-2） vaccination, and cycle threshold（Ct） values of N and ORF1ab genes in the cases were analyzed. Univariate analysis and multivariate Logistic regression were used to analyze the risk factors for hospitalization ＞ 14 days and the risk of not being vaccinated. RESULTS A total of 2896 patients with Omicron variant infection were collected in this study. The average length of hospital stay was（10.79±4.31）days. The average Ct values of N gene and ORF1ab gene on admission were 28.63±6.55 and 29.45±5.50, respectively, and 13.05% of the patients were not vaccinated against COVID-19. The length of hospital stay of the patients with old age was more likely to surpass 14 days. The patients with more times of vaccination were more likely to discharge within 14 days. Nucleic acid testing for COVID-19 showed that the Ct values of the N and ORF1ab genes in the juvenile patients were higher than those in the adult patients, and the Ct values of the genes in the patients with common chronic diseases were lower than those in the uncomplicated patients. Correlation analysis showed that the length of hospital stay was negatively correlated with the Ct values of N gene（r=-0.362,P＜0.001） and ORF1ab gene（r=-0.391,P＜0.001）. CONCLUSION The age of Omicron subvariant BA.2 infection patients, co-morbidity, times of vaccination, and Ct values of SARS-CoV-2 nucleic acid are the risk factors for the length of stay in hospital. Isolation of asymptomatic and mild COVID-19 patients in makeshift hospitals can effectively control the social spread of the epidemic.