Abstract
Background:
Sexually transmitted infections (STIs) remain a major global public health concern. This study aimed to investigate the relationship between sexual orientation and sexual behaviors among patients diagnosed with STIs. Understanding this relationship is essential for clinical practice at the National Hospital of Dermatology and Venereology, as it informs individualized risk assessment, counseling, and preventive interventions across diverse patient populations. In addition, such evidence contributes to the development of targeted STI-prevention strategies that are both culturally appropriate and clinically effective.
Methods:
A cross-sectional descriptive study was conducted with 451 STI patients at the Vietnam National Hospital of Dermatology and Venereology from May to December 2024. Data on patient demographics, sexual orientation, and specific sexual behaviors were collected and analyzed.
Results:
The mean age of participants was 28.73 ± 6.55 years (male:female ratio = 1.73). Syphilis (55.2%), human papilloma virus (HPV; 22.8%), and gonorrhea (20.6%) were the most prevalent STIs. The study found significant associations between sexual orientation and various behaviors. Specifically, heterosexual orientation was associated with non-oral (odds ratio [OR] = 3.01, p = 0.04) and non-anal intercourse (OR = 24.1, p < 0.001). Conversely, homosexual orientation was significantly linked to oral sex (OR = 3.02, p = 0.03), anal intercourse (OR = 22.79, p < 0.001), and lubricant use (OR = 6.2, p < 0.001).
Conclusions:
This study highlights a strong correlation between sexual orientation and specific sexual behaviors, including oral sex, anal intercourse, and lubricant use, among STI patients. These findings are crucial for developing targeted prevention strategies and counseling programs for at-risk populations.
Plain language summary
Why is this research important? Sexually transmitted infections (STIs) remain a significant global public health challenge. To prevent them effectively, we need to understand the sexual behaviors of people who get them. This study aimed to investigate the link between sexual orientation (e.g. heterosexual, homosexual) and specific sexual practices among STI patients in Vietnam. What did we do? We conducted a survey involving 451 patients diagnosed with STIs at the Vietnam National Hospital of Dermatology and Venereology between May and December 2024. We collected data on their age, gender, sexual orientation, and specific sexual behaviors (such as oral sex, anal intercourse, and lubricant use). What are the key findings? The average age of participants was about 28 years, with more male patients than female patients (male:female ratio of 1.73). The most common STIs diagnosed were syphilis (55.2%), human papilloma virus (HPV; genital warts, 22.8%), and gonorrhea (20.6%). The study found clear differences in sexual behavior based on orientation: Individuals with a heterosexual orientation (male-female relations) were significantly less likely to report practicing oral or anal intercourse. Conversely, individuals with a homosexual orientation were significantly more likely to report practicing oral sex and anal intercourse, and they also reported higher lubricant use. What does this study mean? These results confirm a strong connection between sexual orientation and specific sexual behaviors that can increase STI risk. This finding is crucial for public health. It shows we must design STI-prevention strategies and counseling programs that are targeted and culturally relevant to different risk groups, particularly focusing on men who have sex with men (MSM) and the risks associated with anal intercourse.
Introduction
Sexually transmitted infections (STIs) are defined as diseases that can be transmitted through sexual intercourse or from mother to infant during pregnancy or birth caused by bacteria and virus including Chlamydia trachomatis (chlamydia/CT), Neisseria gonorrhea (NG), Treponema pallidum, Trichomonas vaginalis (TV), Mycoplasma genitalium (MG), human papilloma virus (HPV), herpes simplex virus (HSV), and Hepatitis B (HBV). 1 The World Health Organization (WHO) has estimated that the number of incidents with STIs reached approximately 374 million new cases of STIs in 2020, averaging more than one million per day. 2 Among these, the most common infection is Trichomonas’s infections with 156 million new cases per year, followed by chlamydia 129 million, gonorrhea 82 million, and syphilis 7.1 million.1,2
STIs are recognized as a significant global health concern because of its burden on health system, health outcomes, and potential for complications with other comorbidities. 3 The heightened impact of STIs on health includes reproductive complications that can cause infertility, and complications during pregnancy.3,4 In addition, patients infected with HPV are more likely to get cancer. 5 Local symptoms in the genital area can cause discomfort and pain, substantially reducing quality of life and negatively impacting patients’ mental health. Moreover, the cost of treatment and diagnostic tests can have a significant economic impact on health expenditure. 6 WHO has set a goal of ending the STI epidemic by 2030, with key targets including a 90% reduction in the global incidence of T. pallidum (the causative agent of syphilis) and Neisseria gonorrhoeae. 7
Gender is a concept derived from grammatical terminology that refers to an individual’s social identity (such as woman/girl or man/boy), as well as socially shaped personality traits and behavioral patterns (including masculinity, femininity, and androgyny). As a social identity, gender is commonly, though not invariably, associated with biological sex. 8 In contrast, sexual orientation is an enduring pattern of romantic, emotional, or sexual attraction (or both) to men, women, or both sexes. The concept of sexual orientation and issues surrounding sexual minorities have become a sociopolitical issue in Western culture in the 21st century.9–11 Previously research has primarily categorized sexual orientation using three main groups: heterosexual, homosexual, and bisexual. 12 Heterosexuality is understood as opposite-sex sexual relations, that is, male-female (MSW/WSM). Homosexuality will be male-male (MSM) or female-female (WSW) relationships. And bisexuality, for example, means that men can have relationships with both men and women and vice versa (MSMW/WSMW). Till now, there has been very little research on the relationship or difference between sexual orientation, including high-risk sexual behavior (HRSB) and STIs globally or in Vietnam.
HRSB is defined by researchers as sexual activities that involve exposure to STIs including HIV that affect the health of others. 13 The focus of HRSB research is on unsafe sexual behavior and sex with multiple partners citation. 14 The use of stimulants during sex is also considered HRSB. 13 HRSB is relatively difficult to define specifically due to cultural, age, gender, and other factors. 12 However, HRSB is generally considered an important factor closely related to STIs, unwanted pregnancies, or even abortion.13,15 This study will explore the relationship between sexual orientation and unsafe sexual behavior with STIs. Understanding this relationship is essential for clinical practice at the National Hospital of Dermatology and Venereology, as it informs individualized risk assessment, counseling, and preventive interventions across diverse patient populations. In addition, such evidence contributes to the development of targeted STI-prevention strategies that are both culturally appropriate and clinically effective.
Methods
Sample population
All patients who visited the outpatient department at the Vietnam National Hospital of Dermatology and Venereology and were diagnosed with STIs were selected for potential inclusion in the research. Using the Hospital Information System (HIS) software, the research team could contact potential participants directly and by phone to discuss their consent to participate in the study. Eligible participants were individuals aged 18 years or older with a confirmed diagnosis of an STI who voluntarily agreed to participate and provided written informed consent. For participants aged 15 to 17 years, additional written consent from a parent or legal guardian was required. Patients with diagnosed mental disorders, cognitive impairment, or any condition that limited their ability to understand the study information or complete the questionnaire were excluded. All participants were reassured that participation, or not, will not impact their treatment or care, and their information was de-identified and coded to maintain confidentiality and anonymity. Data extraction and contact with participants occurred from May 2024 to December 2024. Of a total of 4267 patients, 1421 agreed to participate in the study. Based on the systematic random sampling method with a sampling coefficient of k = 3, we collected 451 samples that met the criteria to proceed with data collection. The study was approved by the Ethics Committee of the Vietnam National Hospital of Dermatology and Venereology under Decision No. 791/QĐ-BVDLTW.
Research methodology
A cross-sectional descriptive study design was employed, utilizing a systematic random sampling strategy.
Data collection
All 451 participants were interviewed in person or by telephone by researchers. The data-collection form consisted of three main parts: Part A was administrative information extracted from the HIS hospital management software, part B consisted of questions on sexual orientation, and part C investigated sexual behavior. Parts B was based on the Kinsey Scale, a widely recognized instrument for measuring sexual orientation scales and is composed of a single continuum with “heterosexual” on one end and “homosexual” on the other. Parts C was developed by the researchers based on the Biobehavioural Survey guidelines 16 and was completed during the interview and self-administered sections by the participants.
Data analysis
Data analysis was performed using the SPSS 20.0 software, and the analysis was based on descriptive statistics algorithm. Chi-square test was used for categorical variables, t-test was used to compare the mean values of continuous variables, and binary logistic regression analysis was used to compare the relationship. The difference was considered statistically significant at p < 0.05.
Prior to statistical analysis, the dataset was examined to assess the extent and patterns of missing data. Variables with a missing data proportion of less than 5% were handled using complete-case analysis.
Results
Demographics
The study was conducted on 451 patients with sexually transmitted diseases (Table 1). The average age of the patients was 27.73 ± 6.55, ranging from 17 to 59 years. The oldest age group from 50 to ⩽60 accounted for 0.7% of the sample, and the youngest age group from 15 to ⩽19 accounted for 6%. The proportion of men accounted for 63.4%, and women accounted for 36.6%. The proportion of patients from urban areas was 37.5%, and that from rural areas was 62.5%. The average income of patients was 8.86 million VND/month. The proportion of unmarried patients was 51.9%, the married group accounted for 46.1%, and the remaining divorced group for 2.0%.
Social demographics of participants.
Clinical characteristics
Table 2 presents the prevalence of STIs in the total study population, along with the disease history, sexual orientation classification, and sexual behavior.
The prevalence of STIs in the total study population, along with the disease history, sexual orientation classification, and sexual behavior.
Syphilis had the highest prevalence at 55.2%; HPV and gonorrhea had the average prevalence of 22.8% and 20.6%, respectively; and chlamydia had the lowest prevalence of 2.2%.
Of the 451 participants, 190 (43.12%) were suffering from repeated STIs; the prevalence of syphilis, gonorrhea, and chlamydia was 63.2%, 17.4%, and 2.2%, respectively.
The prevalence of heterosexual patients was 89.6%, homosexual patients 10.2%, and bisexual patients 0.2%. Of this population, homosexual men accounted for 8.9%, and lesbians accounted for 1.3%. The average number of current and past 6-month sexual partners was 0.87 ± 0.533 and 1.00 ± 0.627, respectively. The proportion of patients who knew how to use condoms correctly was 87.8%, with frequency of use at all times (7.8%) and occasionally (69.4%).
In Table 2, more than 50% of patients did not use hands, sex toys, lubricants, and time-extending substances or have anal sex or sex with more than one person at the same time. The proportion of patients who used hands during sex accounted for one-third of the total number of patients with STIs. Table 3 illustrates the significance of sexual orientation and sexual behaviors using univariate and multivariate analyses.
Relationships between heterosexual intercourse and sexual behaviors (n = 338).
aOR: adjusted odds ratio; adjusted for age, gender, residence, income, and marital status.
Relationships between sexual orientation and sexual behaviors
In Table 3, the multivariate logistic regression analysis showed a statistically significant association between some sexual behaviors and heterosexual orientation: no oral sex (OR = 3.01, p = 0.04) and no anal sex (OR = 24.1, p < 0.001). Whereas Table 4 presents MSM and sexual behavior analysis.
Relationships between gay or men sex men (MSM) and sexual behaviors.
aOR: adjusted odds ratio; adjusted for age, gender, residence, income, and marital status.
According to multivariate and univariate regression models presented in Table 4, some sexual behavior factors related to MSM are oral sex (OR = 3.6; p = 0.02), anal sex (OR = 25.5; p < 0.001), and use of lubricants during sex (OR = 6.2, p < 0.001). Table 5 identifies the univariate and multivariate significance between the type of relations and potential high-risk behaviors.
Relationships between homosexual and HRSB sexual behaviors.
aOR: adjusted odds ratio; adjusted for age, gender, residence, income, and marital status.
According to the multivariate regression model results described in Table 5, some sexual behavior factors related to homosexual orientation are oral sex (OR = 3.02, p = 0.03) and anal sex (OR = 22.79, p < 0.001).
Summary of results
The logistic regression analysis model showed a statistically significant association between sexual orientation and sexual behavior. Specifically, heterosexual orientation was associated with not using mouth (OR = 3.01, p = 0.04) and not having anal sex (OR = 24.1, p < 0.001), whereas homosexual orientation was associated with oral sex (OR = 3.02, p = 0.03), anal sex (OR = 22.79, p < 0.001); male homosexual orientation with oral sex (OR = 3.6; p = 0.02), anal sex (OR = 25.5; p < 0.001).
Discussion
The findings of this study highlight a predominantly young adult population attending the STI clinic of the Vietnam National Hospital of Dermatology and Venereology, with an age distribution comparable to that reported in previous studies, which have documented a mean age range of 26 to 28.9 years among study participants.3,17 Most patients in the study were male (63.4%). Globally, patient profiles at STI clinics differ in terms of gender distribution: for example, in a large cross-sectional study in China of patients aged 18–49 years, 69.1% of the visitors were female. 18 In contrast, in a study in Northern India, the majority of STI screening seekers were men (71.9%). 19 These differences may be due to cultural and epidemiological factors.
In this study, 62.5% of participants were from rural areas, and 37.5% from urban areas, reflecting differences in socioeconomic conditions. Similar findings were reported by Gupta and Singh, 20 who observed a higher prevalence of STIs among rural populations (70.8%) than among urban populations (29.2%). This disparity may be explained by the geographic distance between rural and urban areas, limited access to healthcare services, low awareness of sexual health, and resource constraints, which often lead rural residents to seek care in urban facilities for better services. 21 These differences underscore the importance of considering socioeconomic and geographic context when designing STI-prevention programs.
In our study, syphilis was the most commonly diagnosed STI, followed by HPV and gonorrhea, while chlamydia exhibited the lowest prevalence. This result is significantly different from that of the study by Fasciana et al. 4 at the STI Unit of the General Hospital “Paolo Giaccone”, Palermo (Italy), in which HPV and syphilis were the two most common diseases, with rates of 55.1% and 45.6%, respectively.
The majority of patients in the study had a heterosexual orientation (89.6%); while homosexual orientation accounted for 10.2%, and bisexuality accounted for 0.2%. This ratio shows that the majority of people visiting the STI clinic were heterosexual, but there was still a significant proportion of homosexual men—a group with a high risk of STI infection. Compared to other studies, the study by Repo et al. 3 in Finland also recorded a high proportion of heterosexuals (91%), while homosexuals and bisexuals accounted for 4% and 1.9%, respectively. This shows consistency between the two studies in noting the predominance of heterosexuals in the STI patient population. However, another study in Spain by Santa-Barbara et al. 17 recorded a significantly higher proportion of homosexuals and bisexuals (12.3% and 4.4%, respectively), reflecting differences in population characteristics, culture, openness in reporting sexual orientation, as well as diversity in health-seeking behavior between countries. Notably, a study by Everett 12 in the United States highlighted the role of sexual orientation in the association with STI incidence. Accordingly, the group of women who have sexual behavior with both sexes and the bisexual group had a significantly higher rate of self-reported STIs than the heterosexual group. 12 This suggests that sexual orientation may not only be a demographic factor but also be closely related to risky sexual behavior and the possibility of STIs.
The majority of study participants (83.8%) reported sexual activity in the past 6 months. This rate is lower than that in international studies such as those in Finland (98.6%) and Italy (98.7%),4,17 which may reflect differences in culture, age, marital status, or the definition of “partner” in the surveys. However, the fact that the majority of participants were sexually active recently also highlights the importance of assessing sexual behavior when implementing STI-prevention intervention programs. Furthermore, with regards to condom use knowledge, up to 87.8% of participants reported knowing how to use condoms correctly. However, the actual frequency of use showed significant differences: only about 8% used them all the time, 69.4% used them occasionally, and 8% did not use them at all. This result is similar to a study in Italy that found 42.5% of participants only used condoms occasionally. Meanwhile, a study in the United States found that the rate of condom use during vaginal intercourse was only about 25%, 22 suggesting that inconsistent condom use is common in many countries. In contrast, the results of a study by Nguyen et al. 23 in Vietnam showed that the level of condom use remained alarmingly low, with 93.02% of people not using or using condoms infrequently. These data suggest that there is a significant gap between knowledge and practice, reflecting the urgent need to strengthen sexual health education toward behavior change.
Regarding specific sexual behaviors, nearly half of the participants (46.6%) had oral sex, while the rate of anal sex was 8.4%, and the use of sex toys accounted for less than 1%. These rates are significantly lower than those in the study by Repo et al. 3 in which up to 76.9% of participants had oral sex, and 14.5% had anal sex, as also noted by Santa-Barbara et al. 17 This difference may be related to the culture, age, or sexual orientation of the study sample, as oral and anal sex are more common among MSM (men who have sex with men). 24
In addition, the rate of lubricant use in our study was quite low; only 10.4% of participants ever used it, in contrast to the study by Ngoc and Son, 25 in which 39.5% of participants reported always using it, and 41.2% used it occasionally. Not using lubricants, especially during anal intercourse or when using condoms, may increase the risk of mucosal injury and STI transmission. This suggests that further health education campaigns are needed to improve understanding and correct practices of lubricant use during sexual intercourse.
Our study noted several statistically significant associations between sexual orientation and sexual behavior. Specifically, heterosexual men were 3.03 times more likely to not have oral sex (p = 0.04), and 24.1 times more likely to not have anal sex (p < 0.001) than the other group. This reflects a clear difference in sexual behavior between sexual orientation groups, consistent with the sexual characteristics recorded in international documents.
A study by Fasciana et al. 4 in Palermo (Italy) also noted that in the homosexual group, the rate of anal sex was up to 99%, and oral sex was 70.3%, with statistical significance p = 0.01. This shows that oral and anal sex are common in the MSM group. Notably, oral sex was also recorded in the lesbian group (55%) and in the homosexual group up to 76.5%. 4 In our study, the rate of oral sex in the homosexual group was 3.6 times higher than that in the heterosexual group, with statistical significance p = 0.02—completely consistent with the trend recorded in foreign studies.
Furthermore, the use of lubricants, according to Thienkrua et al. 26 in Bangkok, showed that 97.1% of MSM used lubricants during anal sex, of which 79.4% used them regularly. Similarly, Rao et al. 27 in Malawi also showed that 25.4% of homosexual men used lubricants during anal sex. Our study results show that the homosexual group is 6.2 times more likely to use lubricants (p < 0.001) than the other group—reflecting the practical nature of sexual behavior in the MSM group, when anal intercourse is a common form and often requires support from lubricants to reduce pain and the risk of mucosal damage.
From the aforementioned analysis, it can be seen that sexual orientation is a factor that significantly affects the sexual behavior characteristics of participants. Identifying the typical sexual behaviors of each orientation group helps to build more appropriate and effective intervention strategies. In particular, the MSM group is still a key target group that needs to be prioritized in communication, education, and STI-prevention intervention programs, with appropriate content on sexual safety, correct condom uses, and lubricant use during anal sex.
Limitations
This study focused on a limited number of STIs, including syphilis, chlamydia, gonorrhea, and HPV, and was conducted at a single national-level specialized hospital, which may introduce selection bias and limit the generalizability of the findings. Patients attending a tertiary referral center may differ in demographic characteristics, health-seeking behavior, or disease severity compared with those at other healthcare facilities. The cross-sectional design does not allow causal inferences, and residual confounding cannot be completely ruled out. Self-reported data may be subject to information bias due to social desirability, stigma, or inaccurate recall, particularly for sensitive sexual behaviors. Future studies should include multiple healthcare sites and larger sample sizes to enhance representativeness and generalizability.
Conclusion
Sexual orientation was significantly associated with sexual behaviors among STI patients, with homosexual orientation—particularly MSM—showing higher likelihood of oral and anal sex than heterosexual orientation. These findings highlight the need for tailored STI prevention and counseling strategies based on sexual orientation and behavior patterns.
Footnotes
Acknowledgements
The authors would like to express their sincere gratitude to all the patients who participated in this study for their valuable time and cooperation. The authors are also deeply thankful to the management and staff of the Vietnam National Hospital of Dermatology and Venereology for their support and assistance in facilitating data collection. Special thanks are extended to the Ethics Committee of the Vietnam National Hospital of Dermatology and Venereology for their approval and guidance throughout the research process.
Ethical considerations
The study was approved by the Ethics Committee of the Vietnam National Hospital of Dermatology and Venereology under Decision No. 791/QĐ-BVDLTW on 17 April 2024. All procedures were performed in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Consent to participate
Written informed consent to participate was obtained from all participants. For participants aged 16–18 years, an additional consent form was signed by their parents or legal guardians. All participants were reassured that their decision to participate or decline would not affect their medical treatment or care. Their information was de-identified and coded to ensure confidentiality and anonymity.
Consent for publication
All procedures performed in this study involving human participants were in accordance with the ethical standards of the national and international research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
Author contributions
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Data availability statement
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.