Introduction
Sexually transmitted diseases (STDs) refer to a group of infectious diseases that are transmitted through sexual contact, cause urogenital lesions and spread through the blood to invade all tissues and organs of the body, even leading to infertility in serious cases [
1,
2]. In the recent decade, the STD spectrum has widened, and more than 20 diseases have been included. For example,
Chlamydia trachomatis (CT) can cause urethritis, neonatal conjunctivitis, cervicitis and infertility;
Ureaplasma urealyticum (UU) is the main cause of nongonococcal urethritis; a variety of bacteria, such as
Gonococcus,
Enterobacter and
Brucella, can be transmitted through sexual behaviour;
Herpes simplex virus (HSV) is a high risk factor of genital herpes; and
Spirochaeta pallidum is the pathogen of syphilis [
3,
4].
The global incidence of sexually transmitted infections (STIs) remains high, with more than 1 million STIs acquired every day [
5]. In developed countries, such as the United States, the rates of
Gonorrhoea,
Chlamydia and
Syphilis have increased, and those of HSV I and HSV II have decreased [
6]. In China, the infection situation of STD pathogens is also not optimistic, and
Ureaplasma,
Neisseria gonorrhoeae (NG),
Chlamydia and other pathogens have reached a certain scale of infection [
7‐
9]. NG, CT, UU and HSV II cause STDs and are closely related to infertility [
5]. The STIs caused by NG and CT are the common causes of vaginitis that can lead to tubal factor infertility, one of the most common causes of infertility that accounts for 30% of female fertility problems [
9‐
11]. UU infection can affect the morphology and quality of male sperms and therefor is an important cause for male infertility [
12,
13]. UU and CT are important pathogens of nongonococcal urethritis. The sexual behaviour may prompt genital tract inflammation in male and female, which is an important factor of infertility [
13,
14]. Genital herpes caused by HSV II easily recurs and can also infect newborns through placenta and birth canal, resulting in congenital infection in newborns.
Some patients infected with UU, CT, NG or HSV II may not show evident clinical symptoms [
6], leading to increased difficulty for the early diagnosis, treatment and control of disease transmission. This study analysed 1736 outpatients in the Reproductive Medical Center of the Affiliated Hospital of Putian University. Real-time fluorescent polymerase chain reaction (PCR) was used to detect UU, CT, NG and HSV II pathogens and analyse the infections of the patients of different genders, ages and diagnoses. A laboratory basis for clinical diagnosis and treatment was provided.
Materials and methods
Study population
After the analysis of the sample information of the patients who visited the outpatient clinic of Reproductive Medicine Center of the Affiliated Hospital of Putian University from December 2021 to April 2023 for a variety of disease causes, a total of 1736 cases were included. Statistical analysis was performed on the nucleic acid detection results of UU, CT, NG and HSV II infection in the samples from 611 male patients and 1125 female patients within an age range of 16–61 (31.36 ± 4.93) years. A total of 1127 secretion samples and 609 exfoliated cervical cell samples, 456 cases of clinically diagnosed male infertility and 909 cases of clinically diagnosed female infertility, and 221 cases related to family planning guidance and 150 cases of other diagnoses were included in this study. The complicated factor of fallopian tubes and uterus were grouped into “Other diagnosis”. The inclusion criteria were as follows: (1) women who did not receive vaginal medication or take anti-inflammatory drugs within two weeks and (2) women who tested positive for UU, CT, NG and HSV II pathogens for the first time. The exclusion criteria were as follows: (1) women with incomplete information and secondary examination and (2) women who had chronic diseases and needed long-term medication. The Ethics Committee of the Affiliated Hospital of Putian University approved this study (No. 2023042), and all procedures were carried out in strict accordance with the Helsinki Declaration.
Sample collection and analysis
For genomic DNA extraction, the samples of secretion or exfoliated cervical cells of the patients were collected in accordance with the instructions. The samples were then thoroughly oscillated and mixed. Volume 320 µL of liquid was absorbed for nucleic acid extraction. Afterward, the DNA (2 µL) was mixed with an amplification reagent. The amplification tube was covered tightly and centrifuged instantaneously. Real-time fluorescent quantitative PCR was used for amplification reaction, and all procedures were carried out in strict accordance with the instructions [
15]. Each amplification required negative and positive references for quality control.
Main instruments and test reagents
The main instruments used in this study included a sample oscillator (Jiangsu Xinkang Medical Instrument, XK80-A), a high-speed freezing centrifuge (Anhui USTC Zonkia Scientific Instrument, HC-3018R), an automatic nucleic acid extractor (Guangzhou Daan Gene, Smart 32) and a fluorescent quantitative PCR (Applied Biosystems, QuantStudio 5).
A nucleic acid extraction reagent (Guangzhou Daan Gene, DA0623) was used for nucleic acid extraction. Nucleic acid test kits for UU (Guangzhou Daan Gene, DA0080-DA0083), CT (Guangzhou Daan Gene, DA0070-DA0073), NG (Guangzhou Daan Gene, DA0060-DA0063) and HSV II (Guangzhou Daan Gene, DA1510) were used to detect the four pathogens, and the operation and result interpretation were carried out in strict accordance with the kit instructions.
Statistical analysis
SPSS 26.0 software and GraphPad Prism 7.0 software were used for data analysis. The counting data were expressed as case number or composition ratio. The χ2 test was used to compare the infection rates among different groups. P < 0.05 was considered to be statistically significant.
Discussion
This study examined 1736 samples from the outpatient clinic of the Reproductive Medicine Center of the Affiliated Hospital of Putian University from December 2021 to April 2023. The results showed that the infection rate was 26.50% for UU, 3.57% for CT, 0.23% for NG and 0.58% for HSV II. The infection was mainly caused by a single pathogen, and co-infection was rare. The overall infection rate of NG pathogens was relatively low, and there was no statistical significance. However, three pathogens of UU, CT and HSVII have attracted our attention.
Studies in different regions of China suggested that
Ureaplasma has a high prevalence [
7]. The UU infection rate (26.50%) was significantly higher than that of the other three pathogens, which was consistent with the situation in Southwest China [
17], Haikou [
18] and Taizhou [
19]. However, there were differences in UU infection rates in different countries. An Italian observational multicenter study revealed that the UU infection rate was only 9% [
20]. A meta-analysis in Iran showed that the infection rate was 17.53% [
21]. The UU infection rates in Moscow (29.1%) [
22] and northeastern Romania (28.46%) [
23] were similar to the results of this study. UU has a high risk of infection for male patients, which is different from the reports in Anhui Province [
24] and Beijing City [
8]、Iran [
21]. UU infection was found in the six age groups, >40 and 36–40 ranked in the top two, and the infection rate ≤ 20 was the lowest. The results of this study were consistent with the highest UU infection rate in the 21–50 age group in China [
25]. The relationship between infection rate and age was slightly different in different provinces of China. For example, the age groups most affected in Anhui Province were 21–30 years old and 31–40 years old [
24]. Compared to other countries, women among the ages of 30 and 35 were the most affected in northeast Romania, followed by those aged 25 to 30. Serbia, Türkiye and Italy have the highest infection rates among 16–39 years old. This difference was related to the geographical and cultural characteristics of the different populations studied [
26‐
28].
Among the outpatients of the Reproductive Medical Center, 78.62% were diagnosed with male or female infertility. The UU infection rate of the patients of different diagnosis groups from high to low was 37.72% in the male infertility group, 27.60% in the family planning guidance related group, 21.89% in the female infertility group and 18.67% in the group of other diagnoses. The difference was statistically significant, indicating that UU infection was closely related to male infertility. The UU infection rate of infertile people in China was significantly higher than the global average [
29]. UU infection was closely related to male infertility in China [
30]. The results of this study were consistent with this view. UU can parasitize in the urogenital tract and enter the seminal tract, seminal vesicle and testis through sexual behaviour, causing inflammation and damaging sperm quality [
31,
32].
Chlamydia is one of the most common STIs in the world. The WHO recorded 129 million new cases of CT infection by 2020 [
33]. The overall CT infection rate in this study was 3.57%, slightly higher than the global infection rate (2.9%) [
34]. In detail, the infection rate of CT in this area was lower than that of Americas (4.5%), but higher than that of Europe (2.7%), Africa (2.6%), Western Pacific (2.6%) and South-East Asia (0.8%) [
34]. CT infection rates in Belgium (1.54%) [
35], Sao Paulo, Brazil (2.2%) [
36] and the United States (2.35%) [
37] were also low, while those in Tanzania (12.9%) [
38] were not optimistic.
The proportion of CT infection is particularly high in young people [
39]. The results of this study also support this view. The risk of CT infection in people aged under 25 years is higher than that in people of other age groups, and its rate decreases with age. CT infection shows a trend among young people, which is similar to the situation in Haikou region [
18]. Globally, the situation was very similar. CT infections in young people aged 15–24 accounted for 2/3 of the total number of new infections [
40]. Similar results have been reported in Russia [
41], Sao Paulo, Brazil [
36] and Germany [
42]. Based on the mode of transmission of CT pathogens, we need to pay more attention to the infection of sexually active women under the age of 25 years [
40] and to strengthen the promotion of health science. Among the patients with male or female infertility, the highest CT infection rates occurred in people aged 21–25 years. The trend of CT infection in younger people is also an important challenge to reproductive health [
43,
44].
HSV type II mainly causes genital ulcer disease. It can increase the risk of HIV infection in men and women and can be transmitted to the foetus during pregnancy which is very harmful to the health of newborns [
45‐
47]. The high seroprevalence of HSV II was found in Zhejiang and Shanghai [
48,
49]. However, HSV II has a low infection rate (0.58%) and is mainly seen in female Putian patients, similar to that reported in Shandong Province [
50]. There were regional differences in HSV II infection rates around the world. Infection rates in the United States [
51] and Europe [
52] have declined recently. Most HSV II infections were in Africa [
53,
54], where the public health burden was greater than in other places.
This study analysed the infection of STD pathogens among the outpatients in the Reproductive Medical Center to help understand the epidemiological trend of the whole region. However, some insufficiencies must be acknowledged. Firstly, the data were derived from the past 2 years, and long-term dynamic observations are lacking. Dynamic analysis for at least 5–10 consecutive years is important for understanding the regional epidemiology; this will be our future research direction. Secondly, the sample size is still limited, and the results may not accurately reflect the region’s overall situation. In our future research, we will continue to collect samples and even adopt multi-centre joint research. In this study, the patients who were tested for venereal pathogens in this centre were mainly concentrated in the reproductive medical centre. The fields of reproductive medicine, such as venereal pathogens and infertility fields, are closely related [
2,
9], which is an innovative perspective for this study.
The number of people infected with STD is annually increasing, and the trend of infection leans toward younger people. Especially in cities with great economic development, young people are open with regard to sexual attitudes and behaviours, but their awareness of self-protection is still insufficient. Therefore, health departments and medical institutions should actively promote publicity and education on sexual health, advocate correct sexual behaviours and encourage regular physical examination among young groups and premarital examination of special people groups to prevent the spread of STDs from the source. These actions will be of great significance to the physical and mental health of young people groups, the growth rate of newborns in China and the prevention of population aging in China.
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