Risk of ******** and Kissing

[zhaodalian]

Dear doctors,

During this summer vacation, I visited prostitutes in Northeastern China quite a few times. Things go like this: The girl gives me a blow job without any protection and then we have vaginal intercourse with a condom. I wear a condom every time. I'm pretty confident that those girls use a condom with at least most clients. However, they never use a condom when they give a blow job.

1.What's the risk of me contracting a STD from a blow job with one encounter? How will you quantify such risk? By the way, each prostitute have 1-hour session with 10 clients every day. I guess it's quite likely that they have some sort of STD.

2.What about the risk of kissing? I know that STDs are rarely transmitted through kissing, but what about other diseases like common cold and flu? Can such risk be quantified?

Thanks