I studied blood types in College, what determines a blood type is it antigens, little pieces around the makeup of your cell, blood type O has no antigens, therefore is the best blood type to use in a blood tranfusion as it adapts to the others, and in return can recieve any blood type back, negative and postive also affect this but I'm not gonna go there, blood type O is the most common blood type in the world, so this is probably the reason why these blood types are statistically shown as being infected more often - because they are the most common! So I wouldn't worry all you other O's! Your antigens and blood make ups have absolutely nothing to do with your immunity as far as I'm aware!
P.S. O postive is the most common blood type, O negative is one of the most rare! Talk about extremes!