Sexually transmitted infection (STI) is one of the most common communicable conditions and has a profound impact on people's sexual and reproductive health (1, 2). More than 1 million new STI cases are reported each day worldwide, of which 50% occurred among young patients (3). Ureaplasma urealyticum (UU), Chlamydia trachomatis (CT), and Neisseria gonorrhoeae (NG) are the most common causative pathogens leading to bacterial STIs, and have gained increasing notoriety owing to their high prevalence (3, 4). About 70% of the sexually active individuals presented with UU in an ongoing carrier state (5). UU is a common commensal colonizing the genitourinary tract and often infects young people after unsafe sexual intercourse. UU infection can lead to infertility, abortion, and other fertility problems in women of childbearing age (6, 7). CT is an intracellular pathogen with an infection rate of 9.8% (8, 9) and of various serotypes (10). NG is the only one among the three pathogens that can be observed under the microscope by gram staining (11) and usually causes urethritis and cervicitis (9).

Timely and effective epidemiologic surveillance can help to make policies for the prevention, screening, and treatment of STIs (3, 12). In China, only a few studies have been conducted to monitor the prevalence of STI pathogens. For instance, a research conducted in Sichuan, which exclusively included female patients seeking care at the Department of Obstetrics and Gynecology, found that UU was identified as the leading cause of STIs (13). However, men are also important reservoirs of STI pathogens, and men who have sex with men (MSM) are seriously affected by STIs because of their particular sexual behavior (3). Therefore, a better understanding of the infection status and epidemiologic characteristics of these pathogens in both men and women is necessary.

This study included 16,216 outpatients attending healthcare facilities from January 1, 2016 to December 31, 2021 to update the prevalence and characteristics of UU, CT, and NG infections in Shanghai. We investigated the distribution of these species in different ages and genders. To our best knowledge, there is no study from Shanghai describing the epidemiologic characteristics of STI-related pathogens separately in men and women over such a long period.

The burden of STIs in China has increased in the past decades (1, 3, 16). STIs are transmitted predominantly via unprotected sexual contact and are closely associated with several urogenital diseases (12), but all STIs are preventable, and most can be effectively cured or treated in case of timely diagnosis (3). Therefore, early detection and surveillance are key cornerstones for controlling STIs. However, most studies only focused on the distribution of pathogens in women, especially in women from the Department of Obstetrics and Gynecology (17), and the long-term epidemiologic features of STI-related pathogens in Shanghai have been rarely reported (18, 19). Enrolling 16,216 outpatients from Shanghai, we described the prevalence of UU, CT, and NG infections from 2016 to 2021 and analyzed the infection types between different genders and age groups to facilitate the development of effective surveillance and prevention strategies for these infections.

Our results revealed the substantial increase in the number of tested women, which may also contribute to the difference in prevalences of STIs among men and women. Accordingly, our study suggested that the monitoring should also be strengthened in men. The prevalence of STIs in our study (35.42%) was higher than that among US adults (about 20% in 2018) (2), indicating that periodic STI surveillance is needed in Shanghai. Researchers have clarified that UU infection can cause inflammation of the female reproductive system (13). Perinatal UU and CT infections can cause abortion, premature delivery, and low birth weight (8, 13). UU and CT are frequent among infertile men and decrease the quality of semen (7, 20, 21). In this study, up to 25% of men with STIs exhibited infertility and adverse pregnancy outcomes, which were the most common complications. However, the latest Chinese guidelines did not recommend screening for STI-related pathogens among infertile couples (22). Hence, we suggest a screening program for infertile couples, especially for men.

Additionally, the overall prevalence rates of UU, CT, and NG in Shanghai were all higher than those from developed countries (2, 23–25), which may be attributed to effective control measures in these countries, such as popularization of sexual knowledge, attention to sexual hygiene, and regular screening of high-risk people. The proportion and prevalence of UU infection were both significantly higher than those of CT and NG infections, which was consistent with previous studies (13, 26, 27). In a study from Beijing, which included patients from 2013 to 2016, the prevalence of the three pathogens was similar to our findings, but in our study, UU and NG infections were more prevalent in men (28). These results indicate that the prevalence may vary in different regions, and the distribution of pathogens can be different in different populations.

Young age has been verified as a strong risk factor for STIs (29). Our results also showed that almost 80% of UU, CT, and NG infections occurred in young individuals aged 21–40 years, similar to those reported from Beijing and Zhejiang, China (28, 30). Nevertheless, we also found a higher prevalence in men than in women in the 21–40-year-old group, suggesting that men aged 21–40 years should undergo UU, CT, and NG screening. Notably, the UU infection was more prevalent among women aged 41–60 years, possibly due to the unique structure of genital tracts and endocrine factors among these women (28). In women aged more than 40 years, STI detection can be considered a supplement to routine physical examination.

In our study, a considerable proportion of infected people, especially women (nearly 20%), had no clinical symptoms, which is consistent with previous findings claiming that female STI is more likely to be asymptomatic (3, 31). Notably, the mean age of co-infected patients (29.98 years) was lower than that of all infected patients (33.23 years), and men were significantly more susceptible to mixed infection, which may be related to the openness to sexuality and the increasing number of young MSM (YMSM) (32, 33). These might reflect a lack of sexual protection and the necessity of sex education, especially among YMSM. Some studies have reported the relationships between STI pathogens. For instance, STI pathogens can increase the risk of HIV acquisition and transmission (28); UU is associated with the persistence of HPV infection and early cytological changes of the cervix (34); and CT colonization contributes to UU or NG infection (30). In our study population, the UU+CT co-infection pattern was dominant, especially among women, where UU played a major role in co-infections. In our study, the distribution of co-infection patterns in women was similar to that in Zhejiang (30). The high prevalence in patients aged 21–30 years suggests that surveillance should be strengthened in this population, and people in their 40s should be cautious of multiple STIs.

In general, UU accounted for the highest proportion of STIs, but its prevalence decreased with aging. The prevalence and infection types varied in age and gender groups. People in their 20s and 30s were most infected with UU, CT, and NG, and the three pathogens were all more prevalent in men than in women. Our findings suggest the screening of UU, CT, and NG for high-risk populations, such as young men, asymptomatic women over 40 years old, and infertile couples. In addition, we illuminated the relationship between gender and STIs to promote the early diagnosis and treatment of STIs and avoid adverse outcomes.

To the best of our knowledge, this was the first study investigating the prevalence of UU, CT, and NG infections among outpatients in Shanghai and analyzing their distribution in different gender and age groups. Information on education, STI history, sexual orientation, condom usage, and sexual partners was not collected, which is the main limitation of this study. The prevalence reported by this study might not be comprehensive enough; thus, further studies are needed to assess the risk factors for these STI-related pathogens in Shanghai and other regions in China.

We demonstrated the high prevalence of STIs in Shanghai and the predominant role of UU. Young men aged ≤ 20 years showed the highest STI prevalence. Different screening, prevention, and treatment strategies are needed for different gender and age groups.

The original contributions presented in the study are included in the article/Supplementary material, further inquiries can be directed to the corresponding authors.

This study was approved by the Ethics Committee of Huadong Hospital Affiliated to Fudan University (Ethics Approval Number: 20190112). The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study.

SuW, HZ, and ShW contributed to conception and design of the study. SuW and JM organized the database. SuW, LD, YL, ZS, WJ, and YM performed the statistical analysis. SuW wrote the first draft of the manuscript. HZ, JM, and ShW wrote sections of the manuscript. All authors contributed to manuscript revision, read, and approved the submitted version.