Welcome to the Forum  I'll be glad to comment.  Trichomoniasis is a relatively common sexually transmitted infection in women which less commonly seen in men.  A recent study stated that about 1/2 of 1% of U.S men between the ages of 18 and 59 have urethral trichomonas.  In men the infection can occasionally cause NGU but the infection is usually asymptomatic and, as you suggest, appears to clear on its own without therapy.  When infection is proven, recommended therapy is 2.0 grams of metronidazole (flagyl) given as a single dose in the way that was prescribed for you.  The medication you took would have cured trichomonas is you had it (odds are high that you did not).

My advice at this point is that there is really no reason to test (even if you had it, you were treated and it would be gone by now) and to move forward without concern.  You are certainly to likely to transit infection to others at this time

I hope that this information is helpful to you.  EWH

1) NAAT sensitivity and specificity for detecting Trich on par with those for Gonorrhea and Chlamydia testing?

2) Any perspective on the transmission efficiency for Trich? Similar to Gonorrhea/Chlamydia? I can gather from prior posts that, while data doesn't exist, very brief encounters as I described (no more than 5 seconds) likely carry even less risk of transmission than that of typical transmission efficiency, correct?

3) What is the purpose of recommending 7 days minimum for avoiding sex when it seems to cure in 3 (that's when I took the Flagyl)? I saw somewhere 2g clears the body in ~44 hours so it makes sense, but why wait 7 days?

If I were to have sex tonight, there seems to be nothing to worry about. Doing my best to let this go!

Thank you again for all of your thoughts.

1.  NAATs are the most sensitive tests for trich and other methods are much less sensitive, making it difficult to give a precise sensitivity or specificity.  The sensitivity of currently available NAATs however is comparable to that of tests for GC/CT.

2.  You are correct.  No precise estimates of transmission rates.  As you point out, logically a shorter exposure should be less risky, other things being equal.

3.  The 7 day recommendation represents tradition more than anything else.  

4.  There are no specific data on the efficacy of flagyl in men.  Efficacy for a single dose as you took is about 90% in women with 7 days of treatment taking the cure rate to >95%.  The assumption is that the infection is easier to transmit in men.

If I were you, I would not worry and encourage you to do your best to move forward.  EWH

Thanks again. Believe me I'm trying to move forward  This is my final follow up, which has quite an update. I learned she was hospitalized for a kidney infection two days after our hookup and was treated/resolved very quickly. Could this indicate any STIs?

She was again evaluted for STIs and came back negative, she says. However I'm not aware of they would have tested for Trich (or even Mycoplasma Genitalium). We've addressed Trich well enough it seems, but would Mycoplasma Genitalium transmit at same rate as other bacterial infections (i.e. 20-30%)?  Following similar logic as before would you confirm that this would also be low risk? 

By the small chance she had it combined with low(?) transmission rate, would Azithro typically cure it at the dosage I had?  

My only physical concern is some slight discomfort in my perineal area (maybe due to anxiety hightening the senses), but no discharge or pain urinating. Ultimately what's the risk I could have anything and transmit to my partner now?

I see resistance is picking up for MGen, but at what rates I don't know. Any last bit of help for those questions, then I'll be done here. Thanks again for all your insight.

Sigh.  Kidney infections are not STIs.  Neither trichomonas nor M. genitalium cause kidney infections either.

The importance of M. genitalium is still a matter of debate other than as a cause of symptomatic urethritis which does not response to azithromycin (thus it should not be a concern for you).  

You are not at risk for transmitting anything to your partner at this time.  

My sincere advice is for your to stop worrying and to stay off the internet.  This will complete this thread.  EWH