<p>Sexually transmitted infections (STIs) remain a major global public health concern. Chlamydia trachomatis (CT), Neisseria gonorrhoeae (NG), and Ureaplasma urealyticum (UU) are among the most common bacterial STI pathogens. Data on the test positivity of these pathogens in reproductive-age populations are essential for informing targeted screening and prevention strategies. This retrospective study assessed the test positivity and co-infection patterns of CT, NG, and UU among 13,622 reproductive-age outpatients in Shantou, China, between January 2023 and December 2024. Urogenital specimens were tested using nucleic acid amplification assays, and associations with clinical diagnoses were examined. Overall, 11.14% of participants tested positive for at least one pathogen; however, as not all participants were tested for all three pathogens (CT: 97.2%; NG: 53.4%; UU: 16.4%), this figure should be interpreted as a likely underestimate of the true positivity in this population. Marked sex differences were observed: CT and UU test positivity was higher in females (3.68% and 48.97%, respectively), whereas NG test positivity was higher in males (15.01% vs. 0.58%). By age, CT and NG test positivity was higher among younger participants (18–24 and 25–30 years) in both sexes, whereas UU test positivity remained consistently high across age groups. Across clinical diagnoses, urogenital inflammation had the highest test positivity for all three pathogens, while infertility-related diagnoses had comparatively lower test positivity. These findings provide evidence to inform targeted STI screening and prevention strategies to protect reproductive health in coastal China.</p>