I read a study that said that of married couples where one had Herpes and one didn't, the other only caught it about 10% of the time. I also figured out that the odds of my having already been with a girl with Herpes, given that 1 in 6 has it, was 99.99999%. Also, Magic Johnson's wife never caught HIV from him.
The truth is, you need to play host to catch a disease. You need to have a compromised immune system. Otherwise, why doesn't everyone have it?
My theory is that when a group of people all catch a disease, it's because they all ate the same diet for a long period of time, and that food poisoning is what causes most flu-like symptoms.
The question is whether you want to date a girl with a compromised immune system, and what damaged her to begin with. Probably prescription drugs and a poor diet.