This topic has been beat up many times and I'm sure it will again.
There are two primary ways that STDs are transmitted. Some diseases, such as HIV infection, Gonorrhea, Chlamydia, and Trichomoniasis are transmitted when infected urethral or vaginal secretions contact mucosal surfaces (such as the male urethra, the vagina, cervix or mouth). In contrast, genital ulcer diseases (such as genital herpes, syphilis, chancroid) and human papillomavirus (HPV) infection are primarily transmitted through contact with infected skin or mucosal surfaces which includes the mouth.
You can get other sexually transmitted diseases (STDs) from oral sex. The more common ones include gonorrhea, Chlamydia, and non-gonococcal urethritis (NGU). These usually can be treated easily with antibiotics. You may also get syphilis (which usually can be treated easily with antibiotics (if identified early enough) and herpes (which can’t be cured but can be treated). Oh and let’s not forget Hepatitis.
You cannot get HIV from contact with saliva alone as current finding show it requires Blood to be involved. The only way oral sex could present some risk is if your sex partner had sufficient amounts of blood in her mouth (from recent dental work or other dental problems for example, poor mouth hygiene) and your penis came into direct contact with blood. But you’d hopefully notice if your partner had blood in her mouth.
And here is the link,
http://www.cdc.gov/condomeffectiveness/latex.htm
For us older guys and some young ones. There is the possibility we have microscopic blood in our semen from our overworked or enlarged Prostate. Sometime that is not seen early.
Bottom line is be safe, drink Wine and Whiskey don't brush your teeth on the day of a date......
Seriously, good up to date information is the best way to understand the risk. CDC is one of the best at giving the latest findings..Then we as Individuals can make a decision we feel comfortable with.