Objective  To analyze the epidemiological features, clinical characteristics and auxiliary examination results of patients diagnosed as Delta strain of Coronavirus Disease 2019 (COVID-19).

  Methods  A total of 75 patients diagnosed as Delta strain of COVID-19 from July 29 to August 16 in 2021 in the fever clinic of Subei People's Hospital of Yangzhou City were included, and they were compared with 37 patients diagnosed as original strain of COVID-19 in February 2020 in Yangzhou City in aspects of epidemiological features, clinical characteristics and auxiliary examination results.

  Results  Among 75 patients infected with Delta strain of COVID-19, there were 26 males and 49 females, with a median age of 50.7(35.0, 67.0) years, including 24 cases (32.0%) aged 41 to 64 years old and 28 cases (37.3%) aged ≥ 65 years old. The median age of patients with the original strain was 46.2(36.5, 55.5) years, among whom 20 cases (54.1%) were 41 to 64 years old. Totally 47 patients (62.7%) diagnosed as Delta strain of COVID-19 had received 1 to 3 doses of vaccine, and 66 patients (88.0%) had a clear contact history after preliminary epidemiological investigation. Totally 34 patients (91.9%) with original strain had a clear contact history. Five patients infected with Delta strain had no clinical symptoms, 54 cases (72.0%) had fever in varying degrees, 39 cases (52.0%) had respiratory symptoms such as cough, sore throat, nasal congestion and runny nose, and 21 cases (28.0%) had neurological symptoms. The age of patients with course of disease at visit >48 h was significantly higher than that of patients with course of disease < 24 h (P < 0.05). The monocyte count of patients with course of disease >48 h was significantly lower than that of patients with course of disease < 24 h, and the platelet count of patients with course of disease >48 h was significantly lower than that of patients with course of disease < 24 h and from 24 to 48 h (P < 0.05). The detection rate of chest CT characteristic inflammation in patients with course of disease from 24 to 48 h and >48 h was significantly higher than that in patients with course of disease < 24 h (P < 0.05). There was no difference in the CT values of open reading frame gene and nucleocapsid protein gene in nucleic acid detection of pharyngeal swab in patients with different course of disease.

  Conclusion  The patients infected with Delta strain of COVID-19 in Yangzhou City are mainly middle-aged and elderly people, and the primary symptoms are mostly fever and respiratory symptoms. Compared with the original strain of COVID-19, patients infected with Delta strain have high incidence of neurological symptoms and rapid progress of pulmonary lesions, and early diagnosis and treatment are recommended.