It would be helpful to know the timing more exactly: when you might have been exposed, when you started taking Bactrim, and when the urine test was done.  Also the dose of Bactrim. If you taking it during the sexual exposure or started it within 2-3 days afterward, it probably would have prevented infection or cured it before a test could become positive. If it was somewhat longer, having been on the antibiotic might have reduced the chance of a positive result, but not by very much. In any case, if you continue the Bactrim for at least a week, then even if you were infected, you probably will be cured, perhaps without ever having a positive test result.

So let me know the details and I probably will have something more to say.

Best wishes--  HHH, MD

Chlamydia rarely lasts more than a few months, especially in men. So the odds were were infected for 7 months is very low. Second, if you were infected, your urine test still would probably be positive after only 3 days of sulfa/trimethoprim (Bactrim). There's still a slight chance it would be falsely negative, i.e. that you really were infected, but it's exceedingly unlikely. Third, your SMX/TMP dose is more than enough to reliably cure chlamydia in about a week. So even if you had been infected and the test missed it, after another 4 days you can be assured you were cured and there would be no risk for your new partner.

Let me know if anything remains unclear. Best wishes in your new relationship!

HHH, MD

You don't mention other STDs. Syphilis and HIV probably are exceedingly unlikely (although of course this depends on your and your partners' sexual histories), but it still would have been reasonable to have blood tests for both. If done and negative, you're good to go!

That completes the two follow-up questions and replies included in each thread and so ends this discussion. I hope it has been useful. Take care and stay safe.