Viral infection. Common world wide. Spread mostly by blood- birth exposure in far east, mid east, africa; bad transfusion (blood supply is tested here;, shared drug use e.g. Needles, contam tattoo ink or needles; less commonly sexually spread. Can cause acute hep: fever, nausea, jaundice, wt loss; may lead to chronic carrier of virus and/or chr. Liver disease. Can lead to cirrhosis, and ca. Rx available; c md.
Lengthy explanation. Hepatitis b usually resolves uneventfully and leaves the patient immune to reinfection, but it can produce chronic hepatitis with potentially serious consequences. You need to learn how they got this, what type of disease process is in progress and for how long if known.