What Causes Recurring Typhoid Fever?

Dear doctor I am suffering from typhoid once every year from past 4 years. I gym regularly, strict diet control is ther. My sgot and sgpt are in normal ratios. But whenever the fever comes it prolonges for more than a week and widal is positive. Also on completion. Of treatment i get vaccinated. However 10 mnths to year and it comes back. Last treatment every year after oral medication is Monocef 2mg thru iv Azithral For 5 ~7 days till fever recedes for 2 consecutive. Days