KLK3 and sexually transmitted disease: PSA levels are known to increase during episodes of symptomatic bacterial prostatitis,[8] and they have been shown to vary by the histological extent of asymptomatic inflammation[9,10] One cross-sectional study of men at an STI clinic found an inverse association between age at first intercourse and mean PSA, as well as a positive association between higher titers of antibodies to Chlamydia trachomatis and PSA values.