Ursodeoxycholic acid is a clinically approved drug which widely used in patients with chronic liver diseases, especially liver transplantation. In China, the COVID-19 infection is in an epidemic state, and the population is generally susceptible to COVID-19. More attention needs to be paid to the prevalence and severity of people taking immunosuppressants after organ transplantation. Recent cohort studies and experiments based on tissue cells, animals and human beings suggest that ursodeoxycholic acid has the potential ability to prevent the entry of COVID-19 into cells, revealing that Ursodeoxycholic acid may be used to prevent the COVID-19 infection. Based on the medical records of patients( already registered on the management website http://www.cltr.org or www.csrkt.org.cn) who received organ transplantation in the First Affiliated Hospital of Xi'an Jiaotong University and the First Affiliated Hospital of Zhengzhou University, this project intends to collect information and data from patients received organ transplantation, aim to understand the COVID-19 infection and severe condition of organ transplantation patients, also explore whether ursodeoxycholic acid has preventive and therapeutic effects on COVID-19 infection and severity rate in patients. This research provides a theoretical basis for further standardizing the prevention and treatment of COVID-19 in patients received organ transplantation.

Inclusion Criteria:

1. Age ≥ 18 years; 2. Patients received liver or renal transplantation from 2015 to 2022

Exclusion Criteria:

1.Age < 18 years; 2. Multi-organ transplantation; 3. Patients with incomplete information or loss of follow-up; 4.COVID-19 infection before organ transplantation; 5. Patients hospitalized with rejection or other infection within two weeks before COVID-19 diagnosis.

Adult patients who underwent liver or renal transplantation from January 1st, 2015, to December 31st, 2022, were retrospectively identified using the database from national transplantation register website and clinical data from the First Affiliated Hospital of Xi'an Jiaotong University and the First Affiliated Hospital of Zhengzhou University.

The study was based on database from The First Affiliated Hospital of Xi'an JiaoTong University and The First Affiliated Hospital of Zhengzhou University, researchers did not have access to patients' information nor raw data unless approved by the Ethics Committee of The First Affiliated Hospital of Xi'an Jiao Tong University.