Clinical Epidemiology, Illness Profiles, and the Implication of COVID-19 Before and After the Nationwide Omicron Outbreak During the Winter of 2022

Abstract Background The outbreak and prevalence of the Omicron variant have threatened human health since March 2022 in mainland China. In this study, we aimed to investigate the clinical characteristics and outcomes of patients with coronavirus disease 2019 (COVID-19) in the Beijing region. Methods In this retrospective study, we enrolled inpatients admitted for COVID-19 in the Fifth Medical Center of Chinese PLA General Hospital in Beijing between November 10, 2022, and January 30, 2023. Demographic and clinical features and treatment outcomes were comprehensively analyzed. We used logistic regression and linear regression analyses to explore the risk factors associated with disease severity and time of nucleic acid conversion, respectively. Results A total of 1010 hospitalized patients with COVID-19 were enrolled. The median age was 43.0 years (interquartile range, 28.0–63.0), and patients aged <60 years and ≥60 years comprised 71.2% and 28.8% of total included patients, respectively. The clinical classification of mild (74.6%, 753/1010), moderate (21.0%, 212/1010), severe (2.7%, 27/1010), and unidentified (1.8%, 18/1010) was separately recorded; 1005 patients were discharged, and 5 patients died in the hospital. The outbreak of the emerging epidemic witnessed an evident increase in the proportion of moderate (42.9% vs. 16.4%) and severe (10.3% vs. 1.1%) cases after December 7, 2022. Patients with a moderate/severe classification had higher levels of procalcitonin, IL-6, serum ferritin, C-reactive protein, lactic dehydrogenase, serum urea nitrogen, and d-dimer and lower counts of CD4+ T, CD8+ T, and B cells (all P < 0.001). Multivariable regression analysis revealed that increased odds of disease severity were associated with the following factors: age ≥60 years, IL-6 > 7 pg/mL, lactic dehydrogenase level >245 U/L, cough, and fever at admission. Age ≥80 years and chronic lung disease were independent risk factors in the nonmild group in elderly patients. In addition, the duration for nucleic acid to turn negative was approximately 5.0 d (interquartile range, 3.0–7.0). Prolonged time of nucleic acid conversion was associated with age ≥60 years, serum urea nitrogen level >8.2 mmol/L, neutrophil count >7 ×109/L, and the presence of a chronic lung disease or carcinoma. Finally, unvaccinated patients accounted for 37.3% of enrolled patients; children and the elder people accounted for approximately half of that. The univariable analysis found that booster doses reduced disease severity and shortened the time of nucleic acid conversion in elderly patients. Conclusions The outbreak of Omicron rapidly increased the number of patients with COVID-19 in Beijing. In elderly patients, booster doses may reduce disease severity and shorten the time of nucleic acid conversion. Healthcare systems should be optimized before an emerging epidemic outbreak.