The goal of this observational study is to test and describe the frequency of hepatitis B virus reactivation in patients who received anti-CD20 drugs for a wide variety of autoimmune and hemato-oncological diseases in order to find out whether a group of patients from a certain field was more sensitive to treatment in this respect than patients from other fields.

Hepatitis B virus(HBV) is the most common chronic virus worldwide. it causes an infection of the liver (hepatitis B) and it is transmitted from person to person through contact with virus-contaminated blood, through sexual intercourse, and vertically from mother to fetus.

Anti CD20 drug or Rituximab is an anti-CD20 monoclonal antibody on the surface of B lymphocytes, which induces cell death (apoptosis) and thus causes depletion. The main side effects of rituximab are infectious and hypersensitivity reactions. It can also increase the chance of hepatitis B reactivation to the point of acute hepatitis.

The information for this retrospective study will be collected from clalit health care's databases.

The patients will be sorted according to the indications for which the treatment with anti-CD20 drugs was given in order to see the differences in the response to the drug in different groups of patient

Inclusion Criteria:

• subjects (men and women) of age 18 and above, who received anti-CD20 (Rituximab) drugs as a treatment for a variety of diseases .

Exclusion Criteria:

• healthy subjects.
• subjects under the age 18.
• subjects who did not receive anti CD20

The population of subjects who received anti-CD20 drugs as a treatment for a variety of diseases between the years 2000 to 2021, within Clalit Health care record database.