I've read your forum off and on for years and it has always been a great service and done a fantastic job of providing factual information and fighting against unneeded fears. 

I think I have a pretty good idea of exposure risks from your answers over the years but I did want to ask about a heterosexual encounter I had with a female in her 30's about 2 months ago that was oral both ways, no insertive sex. I knew they were both a safer form of sex with my highest exposure risks being probably NGU, Gonorrhea and herpes.  I have mostly not worried about that since as I also just happened to be in the midst of taking 100mg doxy twice a day for a week and then took a 400mg cefixime tab for an unrelated issue. I was pretty sure from what I know that would probably kill any risk I had there minus the herpes which I know you only suggest testing if there are symptoms, am I correct here? I've just recently gotten back with a regular partner and having sex and so I guess this is why it's crossed my mind to ask this question now.. I guess some small worries crept in.

My other question is I know I've always read over the years that oral is not an HIV risk. But I feel like I may have seen a few posts that said testing for HIV is such a case was recommended, am I wrong there.  HIV is not something Ive grown up associating with a BJ or cunnlingus? 

You have nicely summarized the facts about oral sex and STI/HIV transmission, and you have correctly analyzed your own risks from the mutual oral sex event you had two months ago. I agree you are at no measurable risk with the possible exception of herpes. But that risk is quite low, probably under one chance in a few thousand for any single oral sex exposure -- both for genital herpes, if your partner had oral HSV1, and oral, if she had an active genital HSV2 infection.

As for HIV, what you have "always read over the years" remains true. Of course some people believe they acquired HIV by oral sex, and for some who performed oral sex on male partners, it's probably true. But it remains the case that to my knowledge there has never been a scientifically documented case of HIV transmitted oral to penis, or by cunnilingus, either to the oral or vaginal partner. I will also point out that the chance your partner had HIV is very low anyway. I would not recommend any STI or HIV testing on account of the event two months ago.

You don't really ask any specific question, but I hope those comments cover your concerns. But let me know if anything isn't clear.

HHH, MD

- My understanding for the girl.. so penis to oral, that HIV isn't a real risk because of the virus being killed by enzymes or acids in the mouth/throat/stomach or something like that... Is that true as well?

- I think I'm fairly versed in what Doxy and cefixime work for, but I do remember reading an interesting post from you a while back with someone else asking about regular treatment with those two. Do both work to fight all bacteria? I believe I've read that each is better for certain bacteria? And then I've always wondered if being on one reduces your chances of infection to begin with.. as an example, if you had taken a 400mg cefixime with 24 hours of an exposure and then say another one after, would that kill an infection?

All antibiotics have selective action, i.e. they inhibit or kill some bacteria, but have no effect on others. The differences have to do with the physiologic mechanism that makes the antibiotic more toxic to some bacteria than others. Taking two antibiotics with differing mechanisms of action, such as cefixime and doxycycline, means efficacy against a broader range of bacteria than either antibiotic alone. But still there are many bacteria resistant to both. However, almost all STI bacteria are susceptible to one or the other of these two drugs. Taking them 24 hours apart would be just as effective as taking them simultaneously.