Introduction:
This study aims to provide further clarifications on some new clinical characteristics of COVID-19 recently discovered by our research group.

Material and methods:
In this single-centred, retrospective study, we collected all confirmed cases of COVID-19 diagnosed in Dazhou, Sichuan, China from January 23 to February 25, 2020. All the cases were either imported from Wuhan or transmitted in family clusters. We analysed general information on all patients. Meanwhile, the contents of lactic acid, Fib-C, and D-dimer in the serum of patients were detected.

Results:
The study included 37 patients diagnosed as having COVID-19, the average age of the patients was 45.76 ±13.1 years. The average positive time of nucleic acid in pharyngeal swabs was 20.65 ±6.7 days. A total of 4 (10.8%) patients were asymptomatic. On serological examination, 33 (89.1%) patients had increased lactic acid, 17 patients had increased fibrinogen C (Fib-C), and 5 patients had increased D-dimer. Of all patients, 29 were positive for COVID-19-specific antibodies. We also detected COVID-19 nucleic acid in faecal specimens from 4 patients. Klebsiella pneumoniae was found in the sputum of 1 patient. A total of 4 patients received psychological intervention. Lopinavir/ritonavir and Abidol may not be effective in treating COVID-19.

Conclusions:
In the serum of most COVID-19-infected patients, lactic acid was higher than normal, and COVID-19-specific antibody was positive. Fib-C and D-dimer in the serum of some infected patients increased. Lopinavir/ritonavir and Abidol have little effect on shortening the positive time of viral nucleic acid in patients.