Abstract
Lifestyle factors have been linked to decreased sperm quality and may influence the prevalence of Ureaplasma urealyticum infection. This study aims to clarify the relationships among Ureaplasma urealyticum infection, lifestyle factors, and semen quality. In this retrospective study, 2668 male partners of infertile couples who underwent fertility evaluation at the Center for Reproduction and Genetics of The First Affiliated Hospital of USTC (Hefei, China) between April 2020 and March 2023 were enrolled. Participants were assessed for semen parameters, clinical characteristics, and lifestyle factors. Of the 2668 participants, 659 (24.7%) participants were positive for Ureaplasma urealyticum. Body mass index (BMI), smoking, and sexual frequency (>2 times per week) were significantly higher in the Ureaplasma urealyticum-positive group than those in the Ureaplasma urealyticum-negative group. After adjustment for potential confounders, smoking (odds ratio [OR] = 1.23, 95% confidence interval [CI]: 1.02–1.49, P = 0.03) and sexual frequency (more than twice per week; OR = 1.41, 95% CI: 1.04–1.91, P = 0.03) remained associated with Ureaplasma urealyticum infection. Regarding semen parameters, ejaculate volume was significantly lower in the Ureaplasma urealyticum-positive group (P = 0.002); however, the prevalence of abnormal semen quality did not differ between the two groups. Logistic regression and restricted cubic spline analysis revealed no significant associations between poor semen quality and Ureaplasma urealyticum infection. In conclusion, Ureaplasma urealyticum infection was associated with certain lifestyle factors but not with semen quality. Further research is required to elucidate the underlying mechanisms and to evaluate potential interventions.
Keywords: lifestyle factors, semen parameters, Ureaplasma urealyticum, smoking, sex frequency
INTRODUCTION
Ureaplasma urealyticum (UU), a member of the Mycoplasmataceae family, is a well-established etiological agent of non-gonococcal urogenital tract infections. Although infections are often asymptomatic, UU can contribute to a spectrum of urogenital disorders, including urethritis and epididymitis. Its prevalence among men aged 16–44 years ranges from 5% to 15%, with higher rates observed in younger individuals.1
Infertility, now affecting over 15% of couples, arises from multifactorial etiologies, among which environmental pollutants such as microplastics and emerging urogenital pathogens are increasingly recognized.2,3,4 Human semen is regarded as an early and reliable sentinel of both individual and environmental health; its cellular and molecular constituents respond rapidly to systemic and local insults, offering a sensitive, minimally invasive readout of reproductive organ integrity and the broader ecological burden of toxicants.5 Among urogenital infections, UU is the most frequently identified microorganism in infertile men.6,7 Recent research has therefore focused on its potential impact on male fertility, particularly its effects on semen quality and overall reproductive health. UU infection has been associated with reductions in sperm concentration, motility, and normal morphology8 and can trigger inflammatory responses within the reproductive tract, leading to elevated seminal leukocyte counts.9 In addition, UU has been implicated in sperm DNA fragmentation, which may compromise sperm function and impair embryonic development.10 Ureaplasma infections are also linked to increased levels of reactive oxygen species (ROS), which induce oxidative stress that damages sperm and diminishes its fertilization potential.11
Lifestyle factors further modulate both the prevalence of UU infection and its impact on semen quality. Smoking has been associated with decreased sperm motility and concentration in primary and secondary infertile men.12 Similarly, alcohol consumption adversely affects semen volume, sperm concentration, total sperm count, sperm motility, and normal morphology.13,14 Notably, UU infection has been statistically associated with smoking.15 Nevertheless, another study report no significant association between UU infection and clinical characteristics such as age, ethnicity, or sexual behavior.16 As research in this area evolves, further investigations are warranted to elucidate the complex relationships among UU infection, lifestyle factors, and semen quality. The present study aims to determine the prevalence of UU infection in men undergoing fertility evaluation, assess its impact on semen parameters, and explore potential associations with lifestyle factors such as age, body mass index (BMI), smoking, alcohol consumption, and sexual activity frequency.
PARTICIPANTS AND METHODS
Participants
This retrospective study enrolled 11 689 males who attended the Center for Reproduction and Genetics of The First Affiliated Hospital of USTC (Hefei, China) from April 2020 to March 2023. Comprehensive data were collected, including semen analysis parameters (i.e., semen volume, sperm concentration, motility, and morphology) and clinical characteristics (demographic profiles, lifestyle factors, and medical histories). The inclusion criteria were defined as: (1) age >20 years and (2) no history of antibiotic treatment within the preceding two weeks. Exclusion criteria comprised: (1) incomplete individual characteristic data, (2) presence of genetic abnormalities associated with male reproductive tract disorders, or (3) diagnosis of azoospermia. The study protocol received ethical approval from the Institutional Review Board of The First Affiliated Hospital of USTC (Approval No. 2023-RE-196). The study was performed in accordance with the principles of the Declaration of Helsinki, and written informed consent for the publication of clinical data was obtained from all participants.
Semen analysis
All ejaculates were collected via masturbation after 2–7 days of sexual abstinence and subsequently incubated at 37°C for a minimum of 30 min to allow for liquefaction. Standard semen parameters, including semen volume, sperm concentration, motility, and morphology, were assessed in accordance with the fifth edition of the World Health Organization (WHO) guidelines for human semen analysis.17 Sperm concentration, progressive motility, total motility, and kinetic parameters were evaluated using a computer-assisted sperm analysis (CASA) system (SAS-II; SAS Medical, Beijing, China). The total motile sperm count (TMSC) was also calculated as semen volume × sperm concentration × progressive motility. Sperm morphology was analyzed using Diff-Quick staining (Anke Biotechnology, Hefei, China), with a minimum of 200 spermatozoa examined per sample. Seminal leukocytes were counted following peroxidase staining with benzidine (Anke Biotechnology). Anti-sperm antibodies (AsAs) were determined by the mixed anti-globulin reaction (MAR) test (Anke Biotechnology). The sperm DNA fragmentation index (DFI) and high-density staining (HDS, immature spermatozoa) were measured by the sperm chromatin structure assay (SCSA; Celula, Chengdu, China).
Detection of UU in semen
All men whose partners are scheduled for assisted-reproduction procedures undergo semen culture for UU. Infection of UU was assessed by seminal culture medium kit (Zhong Ai Sheng Hebei Biotechnology Co., Ltd., Xingtai, China). Briefly, the semen samples were inoculated in the liquid medium, which was subsequently aliquoted into urea and arginine medium to assess the growth of potential pathogens at 37°C with an atmosphere containing 5% CO2. Identification of positive culture was done according to the biochemical test and colony forming unit (CFU) per ml of samples. A threshold of 1 × 103 CFU ml−1 or 1 × 104 color-changing units per ml (CCUs ml−1) or higher was considered as infection.
Statistical analyses
Qualitative variables were presented as frequencies and percentages, whereas quantitative variables were presented as mean ± standard deviation (s.d.) for normally distributed data or median (interquartile range [IQR]) for non-normally distributed data. Comparative analyses were conducted using Pearson’s Chi-square test and Student’s t-test for parametric data and the Mann–Whitney U test for non-parametric data. To evaluate the association between semen parameters and UU infection, logistic regression and multivariate regression models were employed. Covariates incorporated into the models included age, BMI, education level, smoking status, alcohol consumption, sexual frequency, chronic diseases, urogenital infections, varicocele, and redundant foreskin. Subgroup analysis was performed using the stratified multivariate logistic regression analysis. Dose–response relationships between semen parameters and UU infection were assessed using restricted cubic spline (RCS) analysis. A two-tailed P < 0.05 was considered statistically significant. All statistical analyses were performed using Prism 9.0 (GraphPad Software, San Diego, CA, USA).
RESULTS
A total of 2668 males who met the eligibility criteria were recruited in this study (Supplementary Figure 1 (88.5KB, tif) ). The clinical characteristics of the 659 men with UU infection and the 2009 men without UU infection are summarized in Table 1. Statistical analyses showed no significant intergroup differences in age, alcohol consumption, educational level, history of chronic diseases, urogenital infections, varicocele, or redundant foreskin (all P > 0.05). However, BMI, smoking, and sex frequency (>2 times per week) were significantly higher in the UU-positive group than those in the UU-negative group (all P < 0.05). The association between clinical characteristics and UU infection was further investigated using logistic regression analysis (Table 2). Significant positive associations were observed between UU infection and BMI (odds ratio [OR] = 1.03, 95% confidence interval [CI]: 1.00–1.05, P = 0.04), smoking (OR = 1.26, 95% CI: 1.06–1.51, P = 0.009), and sex frequency (more than twice per week; OR =1.46, 95% CI: 1.08–1.97, P = 0.01). After adjustment for potential confounders, smoking (OR = 1.23, 95% CI: 1.02–1.49, P = 0.03) and sex frequency more than twice per week (OR = 1.41, 95% CI: 1.04–1.91, P = 0.03) remained independent risk factors for UU infection. Subgroup analyses were conducted to determine whether the associations between smoking, sex frequency, and UU infection were influenced by age, BMI, alcohol consumption status, education level, the presence of chronic diseases, the presence of urogenital infections, or the presence of varicocele (Figure 1). Interaction testing revealed no significant effects modification, except that the association between smoking and UU infection was influenced by educational level (P = 0.007).
Table 1.
Clinical characteristics of the 2668 participants included in this study
| Clinical characteristic | Total (n=2668) | UU-positive (n=659) | UU-negative (n=2009) | P |
|---|---|---|---|---|
| Age (year), mean±s.d. | 31.9±5.1 | 31.7±5.1 | 32.0±5.2 | 0.15 |
| BMI (kg m−2), mean±s.d. | 24.8±3.6 | 25.0±3.6 | 24.7±3.5 | 0.04 |
| Smoking, n (%) | 0.009 | |||
| Non-smoker | 1429 (53.6) | 324 (49.2) | 1105 (55.0) | |
| Smoker | 1239 (46.4) | 335 (50.8) | 904 (45.0) | |
| Drinking, n (%) | 0.70 | |||
| Nondrinker | 1278 (47.9) | 320 (48.6) | 958 (47.7) | |
| Drinker | 1390 (52.1) | 339 (51.4) | 1051 (52.3) | |
| Education, n (%) | 0.28 | |||
| Middle school or lower | 754 (28.3) | 201 (30.5) | 553 (27.5) | |
| High school | 518 (19.4) | 129 (19.6) | 389 (19.4) | |
| College | 1396 (52.3) | 329 (49.9) | 1067 (53.1) | |
| Chronic diseases, n (%) | 0.06 | |||
| No | 2392 (89.7) | 578 (87.7) | 1814 (90.3) | |
| Yes | 276 (10.3) | 81 (12.3) | 195 (9.7) | |
| Sex frequency (weekly), n (%) | 0.04 | |||
| <1 | 625 (23.4) | 140 (21.2) | 485 (24.1) | |
| 1–2 | 1706 (64.0) | 419 (63.6) | 1287 (64.1) | |
| >2 | 337 (12.6) | 100 (15.2) | 237 (11.8) | |
| Urogenital infections, n (%) | 0.16 | |||
| No | 2392 (86.8) | 583 (87.7) | 1734 (86.3) | |
| Yes | 276 (13.2) | 76 (12.3) | 275 (13.7) | |
| Varicocele, n (%) | 0.56 | |||
| No | 2317 (92.5) | 613 (93.0) | 1855 (92.3) | |
| Yes | 351 (7.5) | 46 (7.0) | 154 (7.7) | |
| Redundant foreskin, n (%) | 0.38 | |||
| No | 1930 (72.3) | 468 (71.0) | 1462 (72.8) | |
| Yes | 738 (27.7) | 191 (29.0) | 547 (27.2) |
UU: Ureaplasma urealyticum; BMI: body mass index; s.d.: standard deviation
Table 2.
Logistic regression analyses for the relationship between clinical characteristics and Ureaplasma urealyticum infection
| Clinical characteristic | Crude | Adjusted * | ||
|---|---|---|---|---|
|
|
|
|||
| OR (95% CI) | P | aOR (95% CI) | P | |
| Age | 0.99 (0.97–1.01) | 0.15 | 0.99 (0.97–1.01) | 0.16 |
| BMI | 1.03 (1.00–1.05) | 0.04 | 1.02 (1.00–1.05) | 0.08 |
| Smoking | 1.26 (1.06–1.51) | 0.009 | 1.23 (1.02–1.49) | 0.03 |
| Drinking | 1.04 (0.87–1.24) | 0.70 | 0.90 (0.75–1.08) | 0.25 |
| Education | ||||
| Middle school or lower | 1.18 (0.96–1.44) | 0.11 | 1.14 (0.92–1.40) | 0.24 |
| High school | 1.08 (0.85–1.36) | 0.54 | 1.03 (0.81–1.30) | 0.83 |
| College | Reference | Reference | ||
| Chronic diseases | 0.77 (0.58–1.02) | 0.06 | 1.35 (1.01–1.80) | 0.04 |
| Sex frequency (weekly) | ||||
| <1 | Reference | Reference | ||
| 1–2 | 1.13 (0.91–1.41) | 0.28 | 1.11 (0.89–1.39) | 0.35 |
| >2 | 1.46 (1.08–1.97) | 0.01 | 1.41 (1.04–1.91) | 0.03 |
| Urogenital infections | 0.82 (0.62–1.07) | 0.16 | 0.83 (0.63–1.09) | 0.19 |
| Varicocele | 0.90 (0.64–1.26) | 0.56 | 0.97 (0.68–1.37) | 0.89 |
| Redundant foreskin | 0.91 (0.76–1.12) | 0.38 | 1.05 (0.86–1.28) | 0.63 |
*Adjusted for age, BMI, education, smoking, alcohol consumption, education, sex frequency, chronic diseases, urogenital infections, varicocele, and redundant foreskin. UU: Ureaplasma urealyticum; BMI: body mass index; OR: odds ratio; aOR: adjusted OR; CI: confidence interval
Figure 1.
Stratified multivariate logistic regression of the associations between UU infection and (a) smoking and (b) sex frequency according to subgroup analysis (adjusted for age, BMI, alcohol consumption status, education level, the presence of chronic diseases, the presence of urogenital infections, and the presence of varicocele). UU: Ureaplasma urealyticum; BMI: body mass index; OR: odds ratio; CI: confidence interval.
A comprehensive comparative analysis of semen parameters was conducted between the two groups. As shown in Table 3, ejaculate volume was significantly lower in the UU-positive group than that in the UU-negative group (P = 0.002), whereas no significant differences were observed for any other semen parameters, including sperm concentration, progressive motility, total motility, TMSC, normal morphology, AsAs levels, DFI, HDS, or seminal leukocyte concentration (all P > 0.05). Furthermore, the prevalence of abnormal semen parameters did not differ significantly between the groups. In addition, no significant differences were found in any sperm kinematic measure, including curvilinear velocity (VCL), straight-line velocity (VSL), average path velocity (VAP), frequency of beat cross (BCF), mean amplitude of lateral head displacement (ALH), mean angular displacement (MAD), linearity coefficient (LIN), wobble coefficient (WOB), and straightness coefficient (STR), as shown in Supplementary Table 1 (all P > 0.05).
Table 3.
Semen parameter values in men from the UU-positive group and UU-negative group
| Semen parameter | Total (n=2668) | UU-positive (n=659) | UU-negative (n=2009) | P |
|---|---|---|---|---|
| Ejaculated semen volume (ml), median (IQR) | 3.1 (2.2–4.1) | 2.9 (2.1–4.0) | 3.1 (2.3–4.2) | 0.002 |
| <1.5 ml, n (%) | 230 (8.6) | 64 (9.7) | 166 (8.3) | 0.25 |
| Sperm concentration (106 ml−1), median (IQR) | 60.3 (30.7–109.8) | 59.9 (32.5–111.9) | 60.3 (30.1–109.5) | 0.55 |
| <15×106 ml−1, n (%) | 319 (12.0) | 72 (10.9) | 247 (12.3) | 0.35 |
| Sperm progressive motility (%), median (IQR) | 36.4 (22.7–50.6) | 37.3 (23.1–51.4) | 35.9 (22.6–50.5) | 0.24 |
| <32%, n (%) | 1103 (41.3) | 252 (38.2) | 851 (42.4) | 0.06 |
| Sperm total motility (%), median (IQR) | 41.2 (26.3–56.9) | 42.1 (27.6–57.7) | 40.8 (26.2–56.7) | 0.24 |
| <40%, n (%) | 1273 (47.7) | 302 (45.8) | 971 (48.3) | 0.26 |
| TMSC (106), median (IQR) | 63.7 (20.3–142.0) | 66.6 (20.8–136.9) | 62.6 (20.2–145.2) | 0.91 |
| <9×106, n (%) | 396 (14.8) | 96 (14.6) | 300 (14.9) | 0.82 |
| Sperm normal morphology (%), median (IQR); na | 7.0 (5.0–8.0); 2641 | 6.0 (4.0–8.0); 654 | 7.0 (5.0–8.0); 1987 | 0.78 |
| <4%, n (%) | 287 (10.9) | 67 (10.2) | 220 (11.7) | 0.56 |
| Seminal leukocytes (106 ml−1), median (IQR) | 0.08 (0.03–0.35) | 0.08 (0.04–0.35) | 0.08 (0.03–0.35) | 0.58 |
| >1×106 ml−1, n (%) | 322 (12.1) | 75 (11.4) | 247 (12.3) | 0.53 |
| AsAs (%), median (IQR); nb | 1.0 (0–3.0); 1956 | 1.0 (0–3.0); 482 | 1.0 (0–3.0); 1474 | 0.11 |
| Sperm DFI (%), median (IQR); nc | 13.0 (8.6–20.4); 1026 | 12.8 (8.4–18.7); 266 | 13.1 (8.7–21.6); 760 | 0.17 |
| >30%, n (%) | 97 (9.5) | 20 (7.5) | 77 (10.1) | 0.21 |
| Sperm HDS (%), median (IQR); nc | 6.7 (5.0–9.1); 1026 | 6.6 (5.0–9.1); 266 | 6.7 (5.1–9.1); 760 | 0.83 |
aSperm normal morphology was available for 2641 of the 2668 enrolled participants; bAsAs was available for 1958 of the 2668 enrolled participants; cSperm DFI and HDS were both available for 1026 of the 2668 enrolled participants. UU: Ureaplasma urealyticum; IQR: interquartile range; TMSC: total motile sperm count; AsAs: anti-sperm antibodies; DFI: DNA fragmentation index; HDS: high DNA stainability
Supplementary Table 1.
Sperm kinematics in men from the Ureaplasma urealyticum -positive group and Ureaplasma urealyticum -negative group
| Sperm kinematics | Total (n=2668) | UU-positive (n=659) | UU-negative (n=2009) | P |
|---|---|---|---|---|
| VCL (µm/s), median (IQR) | 29.4 (19.8–41.7) | 29.9 (19.8–42.3) | 29.2 (19.9–41.6) | 0.51 |
| VSL (µm/s), median (IQR) | 12.1 (7.3–17.5) | 12.5 (7.3–18.2) | 12.0 (7.3–17.4) | 0.36 |
| VAP (µm/s), median (IQR) | 15.6 (9.8–22.4) | 16.0 (10.0–23.0) | 15.5 (9.8–22.2) | 0.41 |
| ALH (µm/s), median (IQR) | 2.2 (1.9–2.4) | 2.2 (1.9–2.4) | 2.2 (1.9–2.4) | 0.45 |
| BCF (Hz), median (IQR) | 7.2 (4.2–10.8) | 7.4 (4.3–11.0) | 7.2 (4.2–10.7) | 0.47 |
| MAD (°), median (IQR) | 13.2 (9.8–16.3) | 13.1 (9.9–16.4) | 13.2 (9.8–16.2) | 0.64 |
| LIN, median (IQR) | 36.3 (29.2–42.4) | 36.4 (30.0–42.8) | 36.2 (29.0–42.3) | 0.33 |
| WOB, median (IQR) | 48.6 (42.8–53.8) | 48.8 (42.0–54.0) | 48.6 (41.8–53.7) | 0.45 |
| STR, median (IQR) | 71.2 (57.3–78.0) | 71.1 (57.8–78.5) | 71.2 (57.2–77.8) | 0.40 |
UU: Ureaplasma urealyticum; VCL: curvilinear velocity; VSL: straight-line velocity; VAP: average path velocity; BCF: frequency of beat cross; ALH: mean amplitude of lateral head displacement; MAD: mean angular displacement; LIN: linearity coefficient; WOB: wobble coefficient; STR: straightness coefficient
The relationship between abnormal semen parameters and the risk of UU infection was further determined by logistic regression (Table 4). Both crude and the adjusted models showed no significant associations between poor semen quality and UU infection (all P > 0.05). Additionally, RCS analysis was used to evaluate possible dose–response relationships between semen parameter values and the risk of UU infection (Figure 2). After adjustment for potential confounders (e.g., age, BMI, education, smoking, alcohol consumption, education, sex frequency, chronic diseases, urogenital infections, varicocele, and redundant foreskin), no significant non-linear relationships were observed between any semen parameter and the risk of UU infection (all P > 0.05).
Table 4.
Odds ratios (95% confidence intervals) for abnormal semen parameter values in Ureaplasma urealyticum-positive men
| Semen parameter | UU-positive | |
|---|---|---|
|
| ||
| OR (95% CI) | P | |
| Crude | ||
| Ejaculated semen volume <1.5 ml | 1.19 (0.88–1.61) | 0.25 |
| Sperm concentration <15×106 ml−1 | 0.88 (0.66–1.15) | 0.35 |
| Sperm progressive motility <32% | 0.84 (0.70–1.01) | 0.06 |
| Sperm total motility <40% | 0.90 (0.76–1.08) | 0.26 |
| TMSC <9×106 | 0.97 (0.75–1.24) | 0.82 |
| Sperm normal morphology <4% | 0.92 (0.68–1.22) | 0.56 |
| Seminal leukocytes >1×106 ml−1 | 0.92 (0.69–1.20) | 0.53 |
| Sperm DFI >30% | 0.72 (0.42–1.18) | 0.21 |
| Adjusted* | ||
| Ejaculated semen volume <1.5 ml | 1.17 (0.86–1.58) | 0.32 |
| Sperm concentration <15×106 ml−1 | 0.85 (0.64–1.12) | 0.26 |
| Sperm progressive motility <32% | 0.86 (0.72–1.03) | 0.11 |
| Sperm total motility <40% | 0.92 (0.77–1.11) | 0.39 |
| TMSC <9×106 | 0.96 (0.74–1.23) | 0.74 |
| Sperm normal morphology <4% | 0.91 (0.67–1.21) | 0.50 |
| Sperm leukocytes >1×106 ml−1 | 0.90 (0.68–1.19) | 0.48 |
| Sperm DFI >30% | 0.77 (0.44–1.27) | 0.32 |
*Adjusted for age, BMI, education, smoking, alcohol consumption, education, sex frequency, chronic diseases, urogenital infections, varicocele, and redundant foreskin. UU: Ureaplasma urealyticum; TMSC: total motile sperm count; DFI: DNA fragmentation index; OR: odds ratio; CI: confidence interval; BMI: body mass index
Figure 2.
Dose–response curves between the risk of UU infection and (a) semen volume, (b) sperm concentration, (c) progressive sperm motility, (d) sperm total motility, (e) TMSC, and (f) normal morphology. Semen parameters were included as natural cubic spline function, adjusting for age, BMI, education, smoking, alcohol consumption, education, sex frequency, chronic diseases, urogenital infections, varicocele, and redundant foreskin. UU: Ureaplasma urealyticum; TMSC: total motile sperm count; BMI: body mass index; CI: confidence interval.
DISCUSSION
In the present study, we analyzed UU infection and semen quality in 2668 men who underwent fertility evaluation. The prevalence of UU infection was 24.7%, consistent with most studies reported that mycoplasmas are present in approximately 25% of semen samples from men seeking infertility care.18,19,20 Among clinical characteristics, smoking and sex frequency (more than twice per week) were significantly associated with the risk of UU infection, whereas age, BMI, education, alcohol consumption, education, sex frequency, history of chronic diseases, urogenital infections, varicocele, and redundant foreskin were not. Notably, no significant differences were observed in any semen parameter or sperm kinetic measure between the UU-positive group and UU-negative group. Both logistic regression and RCS analyses showed no significant correlation between semen quality and UU infection.
Demographic and sexual lifestyle factors have been associated with UU infection in men without nongonococcal urethritis.21 However, another study reported that no difference was detected on the incidence of UU by several clinical characteristics (e.g., age, infertility, varicocele, and genital infections).22 A previous study showed that smoking increased the risk of UU infection 2.9-fold compared with non-smokers in French men,23 which is consistent with our findings that smoking is an independent risk factor in men with UU infection. Smoking impairs urogenital defenses by reducing mucosal immunity, as reflected by reduced IgA levels and impaired natural killer (NK) cell and dendritic cell function. Meanwhile, oxidative stress disrupts epithelial integrity, disturbs the resident microbiota, and fosters an environment conducive to the colonization and persistence of bacteria such as UU, thereby amplifying infection severity.24 Frequent sexual activity also raises the risk of UU colonization or infection, particularly when condoms are not used.25 Our results confirm this positive association. The association is mediated less by the mechanical act of intercourse itself than by behaviors that accompany it, especially inconsistent condom use. This increases mucosal exposure and facilitates pathogen transfer.26 Given that all participants were undergoing fertility evaluation, unprotective sexual intercourse may have further elevated UU risk. Overall, our findings indicate that smoking and high-frequency unprotected sexual activity are positively correlated with UU infection in men from couples seeking conception.
Conventional semen analysis remains the cornerstone for the initial assessment of male fertility potential. Several studies suggest that UU induces mostly asymptomatic, chronic infections that may impair spermatogenesis and reduce semen quality.27,28 UU disrupts the blood–testis barrier, triggering the release of inflammatory cytokines and ROS.29 Infection increases seminal leukocytes, polymorphonuclear elastase, and pro-inflammatory cytokines (interleukin-1β [IL-1β], interleukin-6 [IL-6], interleukin-8 [IL-8], and tumor necrosis factor-α [TNF-α]), amplifying oxidative stress and further depressing sperm concentration, motility, and normal morphology.30 Moreover, ROS-induced lipid peroxidation compromises membrane integrity and epididymal function, ultimately lowering semen quality and fertilizing capacity; this process may represent the underlying mechanism by which UU impairs sperm function.31 Although ejaculate volume was slightly lower in men with UU infection than that in those without, the proportion of samples with volume <1.5 ml did not differ between the two groups. No differences were observed in any other semen parameters or several sperm kinematic variables. Consistent with these findings, several studies have also failed to demonstrate a significant association between UU infection and semen quality.22,32,33 The differing results across studies may reflect variations in study populations, methodologies, and sample sizes.
This study exhibits several strengths. First, the relatively large sample size enhances statistical power and the robustness of the findings. Second, potential confounding factors, such as lifestyle factors and medical history, which have previously been linked to urinary tract infections, were included. These adjustments strengthen the validity and generalizability of the results.
However, several limitations should be acknowledged. First, the retrospective design may introduce selection bias and limit the representativeness of the findings. Second, all participants were recruited from couples undergoing fertility evaluations at a single clinical center, which may restrict the external validity of the results. Third, despite adjustment for several confounders, residual confounding (e.g., environmental pollutants34) and the influence of unmeasured factors cannot be excluded. An additional limitation is the exclusive use of CASA without complementary manual assessment. Although CASA provides objective and reproducible measurements, manual evaluation remains the gold standard in many settings. Reliance solely on automated systems may introduce measurement bias, particularly for sperm motility and morphology parameters. Moreover, while the use of culture methods for the diagnosis is conventional, it is time-consuming and has lower specificity than molecular techniques such as polymerase chain reaction (PCR) assays. Lastly, the worldwide coronavirus disease 2019 (COVID-19) pandemic occurred during the study period, and accumulating evidence indicates that severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection can transiently impair semen quality;35,36,37 this context may have influenced the results reported herein.
In conclusion, our study identified significant associations between lifestyle factors, smoking and sexual frequency, and UU infection. However, no significant relationships were observed between semen quality and UU infection. Further research with more comprehensive data collection is needed to clarify these relationships.
AUTHOR CONTRIBUTIONS
XHD and SB designed the study. SB contributed to the data acquisition. XHJ, LZ, YYT, QJ, WJT, LMW, and BX analyzed the data. SB and BX wrote the original manuscript. XHD, XHJ, BX, and SB have verified the underlying data. All authors read and approved the final manuscript.
COMPETING INTERESTS
All authors declare no competing interests.
Flow diagram of the study. UU: Ureaplasma urealyticum.
ACKNOWLEDGMENTS
This study was supported by the National Natural Science Foundation of China (No. 82201792) and the China Postdoctoral Science Foundation (No. 2024M763169).
Supplementary Information is linked to the online version of the paper on the Asian Journal of Andrology website.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Flow diagram of the study. UU: Ureaplasma urealyticum.