Honorifics question

I'm a little confused as to this exchange.

Person A: Oisha-san desu ka?
Person B: Hai, Watashi wa isha desu.

I'm a little confused as to the usage of "o" before the word "isha". Is it honorific? If it is, why wouldn't the usage of "san" when addressing that person suffice? Thanks in advance everyone.

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hm, I just tried saying it without the お～ and it seemed rather strange. If you were asking for someone by name, you wouldn't use 美化語 with their name, but perhaps the お～ isn't necessarily meant to honor the person, but the profession of being a doctor itself. 美化語 is pretty widely used to just polish up words to make them sound more formal or polite, and as a common noun, it's ripe for slapping a little honorific on the front to make it sound better.

And if you don't like that explanation, Mike's post sums it up pretty well