Doctors. I am going to keep this factual and as brief as required.

I am a 42 year old married caucasian male. I have been married for 17 years and haven't once strayed from my wife. About 90 days ago I attended a conference for work and met a 40 year old, married (white) woman with teenage children. She works as a mid-tier professional at a large company. After many drinks, we ended up in my room and had brief, unprotected vaginal sex. The sex itself lasted about 30 seconds (max) and I refused to continue. I should also note: before we began our "fun", she told me she had her tubes tied. I also asked about STIs, to which she laughed and claimed "I am married. I haven't been with anyone else and I have never had an STD". She was, if anything, humorous about the inquiry. She did say however, that she has been with women before. She seemed absolutely unphased after and not worried at all.

I met with my PC physician and told him the story. I was a wreck. He implored me not to worry - that her age, marital status, and profile was incredibly low risk for HIV and other STIs. He told me to abstain from sex for 30 days, watch for symptoms and (if none) that I was 99.9% in the clear. 

It's been 90 days and I haven't felt a thing and have resumed sex with my wife.

Questions:

1. I found stats via the CDC that support my DRs position. Gonorrhea, Chlamydia, Syphilis and HIV are incredibly rare in 35+ women, particularly if they are Caucasian and not defined in any other high-risk category. Combining this with rather low, single-exposure transmission rates (20-30% for G&C), the statistics indicate that there is very low risk for everything (1 in many million for HIV/Syph and 1/5000 or a 0.025% chance of G or C). Does this ring true to you or am I butchering the odds? Of course, there is always a chance, but odds this low are reassuring if true.

2. I am more concerned about Trichomonas. Until this event, I hadn't heard of this infection. There is virtually no research available to satiate my need for stats. I have read, in many places, that the infection is much less common in causasian women. I have also scanned this forum for answers, and I have seen that it is quite rare to "pick up" trich from a single exposure. I believe Dr. HHH made this statement in a post from a few years back (a "one in many thousands" risk). Should this be of concern to me or should I move on? I had no idea how prevalent Trich is and how seemingly common it is in older women.

Thank you for your consideration.

After re-reading my message, I believe it came off as over confident and bloated.

Believe me, I am worried. I have no idea what I am really talking about and I appreciate your services. I am hoping this ridiculous and out of character slip-up will not harm my wife or our relationship. I am an idiot.

I agree exactly with your PC physician:  this was an exceedingly low risk sexual encounter wiht a partner who is very unlikely to have any STD. He was more conservative in his advice than I would have been. Had you asked right after the event, I would have advised no need to hold off on sex at home at all -- or certainly not beyond 10 days or so.

1. I'm glad you have found epidemiologic data that have helped convince you of the low risk. For what it's worth, though, your one-time partner's sexual history and what you know of her lifestyle are more important than the frequency of STIs in women of her age. Your risk estimate for gonorrhea and chlamydia is much too high, because it doesn't seem to incorporate the fact that absence of symptoms is additional strong evidence. I'd put the chance you have either of these as well under one in a million. Of course you are free to have a urine test for both if a negative result would further reassure you. 

2. I agree there are few available data on trichomonas, but I don't understand why you are concerned about it. You give good reasons yourself. I don't know the context of my previous "one in many thousands" estimate, but the risk undoubtedly is at least that low or lower. That trich is diagnosed fairly frequent in "older women" is not evidence it is likely in your partner. Here too, you could have a urine PCR for trich if the negative result would help you get beyond these concerns.

I hope these comments are helpful. Let me know if anything isn't clear.

HHH, MD

1. In reading about age association and STD prevalence, I always understood there were factors that influenced lower numbers (biological susceptibility, prior infection/immunity). Either way, if I take my one-night partner's word, it seems unlikely she was been with other men outside of her marriage.

2. Why my concern about Trich? I came across all sorts of internet literature on the infection this weekend. It caught me off guard. I had, as my physician suggested, moved on. It seems like an ultra common infection and the asymptotic nature of it is a bit troublesome. I just hope I haven't acquired it and passed it to my wife. Is it unlikely to catch during such a brief, single exposure?

Thanks again.

2. "Ultra common" is appropriate in some ways in regard to trichomoniasis, otherwise not so much. Because so many infections go undiagnosed for months or years, the prevalence -- the number of infections existing at a point in time -- is very high, although much more so in resource poor settings like third world countries than in the US. Indeed, by some estimates the highest prevalence of all STDs that cause genital symptoms like vaginal discharge. However, as best we understand the limited data available, the incidence, i.e. the frequency of new infections, is low -- probably a lot less than chlamydia or gonorrhea, for example. Although no data are available to estimate the chance of infection from a single non-monogamous sexual encounter, almost certainly it is very low. And from what you say about your partner, it seems very unlikely she has it. As I said above, you are free to have a urine PCR test if the expected negative result would increase your confidence about it.

The other aspect about trich to keep in mind is that it generally is harmless, with few significant complications in women and none known in men. Having it is a nuisance for infected women with symptoms, but that's about it. (Having trich modestly raises the chance of catching HIV if exposed, but that's a trivial issue in industrialized countries and not an important aspect of the infection.)

Last question (I know I am out of ammo after this one): I called my PC today and asked about Trich. He was, as expected, not concerned.

You placed some fairly astronomical odds on the acquisition of G and C from this brief exposure. Would you think Trich is more likely? When I hear 1 in a million, naturally I see no point of worry.

I should also note: My doctor also told me that the infection, when present in men, can clear very quickly. He also said that he rarely, if ever, has seen it diagnosed in men without repeated exposures to an infected (female partner). 

I agree with the first statement you attribute to your doctor. I'm not sure about the second statement. All STDs are more frequent following multiple exposure than only one. STDs are transmitted inefficiently, i.e. any single exposure to an infected partner usually doesn't result in transmission. For gonorrhea (female to male by vaginal sex) it's around 50% chance for any one exposure; it's ~20% for chlamydia; and under one in a thousand for HIV and herpes. I'm not sure where trich lies on this scale, but probably roughly like gonorrhea or chlamydia. For all of them, the likelihood of becoming infected obviously rises with the number of exposures.

That concludes this thread. I hope the discussion has been helpful. Best wishes and stay safe.