I had non-protected vaginal sex (once) with a 44 old female on a business trip.  She was not a CSW, but I don't otherwise know her sexual history.  I just received blood and urine test results taken at day 28, all of which came back negative.  I haven't had any symptoms.  I understand from this forum that HIV and syphilis should be tested after 6 weeks.  1) In these circumstances, would you recommend that I re-test again after 6 weeks?  2) If so, would that be considered conclusive at that time?  It sounds like waiting 12 weeks is unnecessary and too conservative.

Thank you for the great work you do.

STDs are rare in persons over 40 years old -- so on that basis it is unlikely your partner had a transmissible STD. Second, you don't mention symptoms like discharge from the penis, painful urination or penile sores; that alone makes the chance you caught anything very low. Third, your negative urine tests probably were for gonorrhea and chlamydia and were conclusive. Fourth, your negative blood tests presumably were HIV and syphilis -- although a bit early to be conclusive, those results were at least 95% reliable. (Combining that fact with lack of symptoms, makes both infections exceedingly unlikely.) 

I would have advised against any need for testing at all. But having done that, probably you should repeat the HIV and syphilis test at 6 weeks, for 100% conclusive results. (This assumes your HIV test was an AgAb [4th generation] test; if it was an antibody-only test, repeat it at 8 weeks.) You do not need any further testing at 12 weeks or any other time.