Clinical characteristics of COVID-19 in Osaka, Japan: Comparison of the first–third waves with the fourth wave

BACKGROUND: The fourth wave of COVID-19 in Osaka Prefecture, Japan, caused a medical crisis. Here, we aim to identify the risk factors for COVID-19 severity and compare patients between the first–third waves and the fourth wave. METHODS: We performed an observational retrospective study of COVID-19 cases at the National Hospital Organization Kinki-Chuo Chest Medical Center. RESULTS: We identified 404 patients (median age: 71.0 years [interquartile range: 56.0–80.0]), of whom 199 (49.1%) had mild disease, 142 (35.2%) had moderate disease, and 63 (15.6%) had severe disease. The overall mortality rate was 5.4% (22/404). Based on multivariate logistic regression analysis, cardiovascular disease, fever, dyspnea, and several inflammatory biomarkers were independent risk factors for moderate to severe disease. For every 1 mg/dL increase in C-reactive protein, 10 IU/L increase in lactate dehydrogenase, and 100 ng/mL increase in ferritin, the risk for moderate to severe disease increased by 18.3%, 12.9%, and 8.9%, respectively. Overall disease severity in the fourth wave was higher than in the first–third waves. However, there was no significant difference in mortality. Because of a shortage of beds, four of the 28 severe patients (14.3%) in the fourth wave could not be transferred to the advanced hospital. CONCLUSIONS: Cardiovascular disease, fever, dyspnea, and several inflammatory biomarkers were risk factors for moderate to severe COVID-19 in our cohort. During the fourth wave, COVID-19 severity worsened, increasing the number of patients who could not be transferred to beds for severe cases, resulting in a medical crisis in Osaka.