Australia antigen is a marker of hepatitis B infection. This can be acquired by various parentral routes viz. through blood transfusion, by way of any surgical procedure ranging from dental procedures to major operations,tatooing,in drug addicts by sharing needles and by having unprotected sex. If you are unimmunized then first get yourself tested for HbsAg. If negative then undergo an immunisation schedule comprising of 3 doses. After completion of the immunisation schedule get antibody titers done. If above 10 then you are well protected. Avoid all high risk activities as already advised.