回复：if you don;t have hepatitis B before,

most likey you got infection in US. Hepatitis B was spread through repeated uses of syringes in some clinic which reported a couple of weeks ago.
It is better to check hepatitis B whole panel, looking at the status of HBsAg, HBsAB, HBeAg, HBeAB and HBcAb, then decide what you should do.
If only HBsAg postitive, others are negative, you are called healthy carrier.
if HBsAg and HbeAg positive, most likely your virus reproduction is active, under this circumstance, you should check your DNA level, and ALT level to decide if you need to be treated or not.