Etiological spectrum of sexually transmitted infections in infertile men: a monocentric retrospective study

Background : Sexually transmitted infections (STIs) have been linked to male infertility; however, the available evidence from Eastern Europe is inconclusive. Aim : The present study therefore set out to assess the prevalence and etiology of STIs, focusing on Trichomonas vaginalis , among infertile Bulgarian men. Materials and methods : A retrospective monocentric study was conducted at Thorax Hospital, Plovdiv, between May 2018 and May 2024, on 359 infertile and subfertile men. The study adhered to the World Health Organization (WHO) guidelines for the evaluation of semen parameters. Ejaculate, prostatic secretions and urethral swabs were subjected to a culture and microscopy procedure for 16 pathogens. The associations between semen quality and these parameters were examined using t-tests, chi-squared tests and logistic regression. Results : Sexually transmitted infections were detected in 48.5% (174/359). Frequent pathogens were Ureaplasma urealyticum (29.5%), group B streptococcus (25.1%), Enterococcus spp. (13.9%), and coagulase-negative staphylococci (CoNS) (13.9%). The prevalence of T. vaginalis was 6.7% (24/359) and associated with lower progressive motility (β=−7.66 percentage points; p =0.028, uncorrected). Coinfections occurred in 42.1%, monoinfections in 39%. Prostatic secretions were more often positive than ejaculate (54.7% vs. 46.9%; p =0.06). No significant between-group differences were seen for sperm concentration (43.9 vs. 46.7 million/mL, p =0.307) or symptoms (21.3% vs. 27.6%, p =0.206). Multivariable models found no independent clinical predictors (all p >0.05), while pathogen burden correlated with motility (r =−0.152, p =0.004). Conclusion : Sexually transmitted infections (STIs), particularly U. urealyticum and T. vaginalis , are common in infertile Bulgarian men and often remain asymptomatic. Routine broad-spectrum screening, including prostatic sampling, is warranted to detect treatable causes and potentially optimize fertility outcomes. Prospective studies should determine whether the eradication of these infections improves semen quality. These findings emphasize the necessity for standardized, comprehensive diagnostics and meticulous interpretation of colonizers versus pathogens in infertility evaluations to inform management decisions.