Increasing incidence rates of sexually transmitted infections from 2010 to 2019: an analysis of temporal trends by geographical regions and age groups from the 2019 Global Burden of Disease Study

Sexually transmitted infections (STIs), including syphilis, chlamydia, gonorrhea, trichomoniasis, and genital herpes, are globally a major public health problem. Chlamydia trachomatis and Neisseria gonorrhoeae (N. gonorrhoeae) infections have a detrimental influence, including disseminated infection, tubal-factor infertility, pelvic inflammation, and ectopic pregnancy [1‐4]. The risk of acquiring or transmitting human immunodeficiency virus infection may greatly increase due to the presence of STIs [3]. Generally, STIs severely impair the quality of life, with physical, psychological, and social consequences [3]. Although chlamydia, gonorrhea, and syphilis as bacterial STIs and trichomoniasis as a parasitic STI can be cured using existing drug regimens, drug resistance may threaten the possibility of them being cured [1]. For example, uncomplicated gonococcal infections may become uncurable when strains with multi-drug and extensive drug resistance become dominant [2]. In addition, antiviral drugs only mediate, not cure, genital herpes infections [1].

Therefore, preventive approaches have become preferable for inhibiting the acquisition of STIs [1]. Developing vaccines is a priority, but vaccinations are not yet available [2]. In 2016, the World Health Organization (WHO)’s Global Health Sector Strategy on Sexually Transmitted Infections pointed out that N. gonorrhoeae infections require immediate action for control due to the rising risk of untreatable gonorrhea and co-infection with other STIs [3]. This report also recognized the increasing rate of chlamydial infection in adolescents [3]. The WHO highlighted a 2030 goal of ending STI epidemics, with key targets including a 90% reduction in Treponema pallidum (T. pallidum) incidence and N. gonorrhoeae incidence globally (from the 2018 global baseline) [5]. Given that the regional and age differences in STI burden may vary, the WHO proposed a priority focus on obtaining better data on STI burdens by age group to assess progress toward STI control [5]. Moreover, the immense burden of STIs may be distributed disproportionately at the geographical and age levels due to income, health services, lack of treatment, and stigmatization [1]. However, a description of the latest trend characteristics of STIs at the geographical and age levels is lacking.

To identify priority areas for action, we described the current epidemic status and features of 5 STIs, including syphilis, chlamydia, gonorrhea, trichomoniasis, and genital herpes, and further analyzed the temporal trends from 1990 to 2019 by geographical (global, regional, and national level) regions and age groups using data from the 2019 Global Burden of Disease (GBD) study [6]. This study sought to provide a comprehensive perspective reference on targeted control strategies by compiling an extensive and complementary report on the landscape and long-term trends in global, regional, and age differences in STI incidence.

To our knowledge, this is the first study to assess the long-term trends and differences in incidence rates of STIs, including syphilis, chlamydia, gonorrhea, trichomoniasis, and genital herpes, by geographical (global, regional, and national) regions and age groups using data from the 2019 GBD study. This paper focused on trends in STI incidence over the past decade at regional and age levels, highlighting that targeting prevention strategies to regions and age groups is vital for controlling STIs in the future.

We found that the ASRs of syphilis, trichomoniasis, and genital herpes were highest in low SDI regions from 1990 to 2019, while those of chlamydia and gonorrhea were highest in middle SDI regions from 1990 to 2019. The above information indicates that STIs remain epidemic in lower-income regions. Our study examines the trend of STIs from 2010 to 2019. We found that the trend of ASRs of syphilis, chlamydia, trichomoniasis, and genital herpes was increasing worldwide from 2010 to 2019. Notably, the greatest increase in ASRs of syphilis (tropical Latin America), chlamydia (high-income North America), and gonorrhea (high-income North America) all occurred in American regions. Tropical Latin America includes Brazil and Paraguay, which are both middle SDI regions. The SDI region with the greatest increase in ASR for syphilis was the middle SDI region, and Brazil. Swayze et al. observed that annual cases of syphilis in pregnant women increased between January 1, 2010, and December 31, 2018, in Brazil [14]. Brazil reported 724,310 acquired syphilis cases from 2011 to 2019 [15]. Meanwhile, the greatest increase in ASRs of chlamydia and gonorrhea occurred in high-income North America. Routine public health surveillance reported that chlamydia incidence rates increased from 394.9 per 100,000 people to 476.2 per 100,000 people and gonorrhea case rates increased from 78.0 per 100,000 people to 143.5 per 100,000 people from 2007 to 2016 in Winnipeg, Canada [16]. In other words, chlamydia was widespread geographically and gonorrhea was in a growth phase with geographic dispersion in Winnipeg, Canada, from 2007 to 2016 [16].

Furthermore, this study found that the population with the highest incidence of different STIs seemed to have changed by 2019 compared to that known 10 years ago. For syphilis, patients tended to be younger globally but older in North Africa and the Middle East. From 2014 to 2018, the population with a high incidence was aged 25–34 years but in 2019 was aged 20–24 years in China [17]. However, many studies have reported that the population with a high incidence of syphilis may be older in countries of North Africa and the Middle East [18]. Additionally, chlamydia population tended to be older in southern sub-Saharan Africa but younger in Australasia. There were some studies on age-related changes in the incidence of chlamydia in some countries of Australasia, including Australia [19, 20] and New Zealand [21]. Population with genital herpes tended to be older in high-income North America and South Asia in 2019. Few studies found that the percentages of patients with the herpes simplex virus were greater among older age groups in Eastern India [22] and Canada [23]. Previous studies usually divided age groups as < 20, 20–24, 25–44, and > 44 years, respectively, so it was found that the population with a high incidence was those aged 25–44 years, and is difficult to compare the change in the age group with a high incidence [24, 25]. The WHO proposed that there should be a priority focus on obtaining better STI data by age groups because of the need to measure progress toward STI control [5]. Our study not only highlighted the need for age-specific control measures in different regions, but also the need to strengthen STI surveillance in different age groups.

To control STIs, first, we should pay attention to reducing the percentages of high-risk sexual behaviors, especially among the youth. Peltzer et al. recorded increases among female adolescents in the prevalence rates of ever having sexual intercourse (from 24.4 to 36.4%) and having multiple sexual partners (from 13.6 to 16.9%) from 2007 to 2018 in Argentina [26]. Sharma et al. [27] reported that high-risk sexual behaviors have increased among adolescent boys (from 64 to 70%) and young men (from 18 to 27%) from 2005 to 2015 in India. It is very important to strengthen sexual health education in schools, including functional knowledge and skills to practice, adopt, and maintain healthy behaviors for preventing STIs [28, 29]. As most adolescents use mobile phones in their day-to-day lives, professional apps that provide an anonymous, free, and voluntary platform for information were considered [30, 31]. Additionally, getting treatment for partners may be effective in reducing STI incidence in youth [32]. Second, effective STI prevention interventions include screening, contact tracing of sexual partners, and promoting effective barrier contraception [33]. STI counseling and testing lead to positive sexual behavior changes [34]. Therefore, improving the quality rather than quantity of primary health care is particularly important. For example, incorporating sexual pleasure or security considerations within programming may have a positive impact on condom use, which has direct implications for reductions in STIs [35]. Moreover, the screening and testing of some high-risk populations, including men, transgender female sex workers, bisexual people, and other men who have sex with men are important regardless of self-reported sites of potential exposure [36, 37]. For bisexual people and men who have sex with men, the need for systematic multisite screening, regardless of symptoms, is also crucial [38]. Therefore, when resources are sufficient, monitoring work should be carried out among different populations according to location [36].

The data used for analysis were extracted from the 2019 GBD. We supplemented a comprehensive understanding of the incidence of STIs and further tried to develop global targeted prevention strategies. However, our study had several limitations. First, its main limitation is the accuracy and robustness of GBD estimates. The quality and quantity of GBD data largely depend on the data used in the modeling [11]. If countries lacked sufficient national systematic surveillance and population-based studies, the model may have a margin of bias. Furthermore, data derived from national epidemiological surveillance systems may be highly heterogeneous because of the differences in the quality of clinical and laboratory diagnostics, laboratory quality, and reporting standards among different countries, so the plausibility of the results would be influenced [12]. Second, because GBD data was estimated by modeling, an ecological fallacy may exist. Finally, sex is an important aspect in the spread of STIs, we only provided the trend of five STIs in female and male at global level, but did not conduct an analysis in depth. The analysis of STIs according to sex between different regions and age groups should be strengthened in the future.

In this study, we found that the global trends of STIs—including syphilis, chlamydia, trichomoniasis, and genital herpes—all showed increasing ASRs from 2010 to 2019, which indicates a big challenge for controlling STIs in the future. Additionally, the differences in trends existed by geographical regions and age groups. American regions faced a big burden with a trend of the greatest increase in ASR for syphilis, chlamydia, and gonorrhea. Southern sub-Saharan Africa and East Asia had the greatest increase in ASR for trichomoniasis, and genital herpes, respectively. Moreover, in the most recent years, the population with high incidence rates of syphilis, chlamydia, and genital herpes tended to be younger or older in some regions in 2019. Therefore, a better understanding of STI epidemiological patterns is urgently needed for planning and implementing prevention and control strategies in key regions and population groups. Furthermore, to reduce the burden of STIs, it is essential to strengthen sexual health education and developing STI surveillance for key regions and populations.