9 months ago bv was detected not trich in vaginal swab .i havent had sex for 9 months. now, i have checked, trichomonas came positive in tests (pap and vaginal swab). so the question: is trichomonas hard to detect sometime. reinfection not possible.

Trich diagnosis: What test was done with your "vaginal swab" test 9 months ago? If that was an attempt to find trichomonas looking at vaginal fluid under a microscope, that test misses at least 50% of all trich infections. Maybe this time you had a DNA test for trich, which is much more accurate. Trichomonas and BV cause similar symptoms (primarily discharge with odor). Probably you had trich all along.