Understanding the Global Challenge of Sexually Transmitted Infections (STIs)
Key Facts
Every day, more than 1 million curable sexually transmitted infections (STIs) are acquired worldwide among individuals aged 15 to 49, and a significant number of these infections are asymptomatic. In 2020, it was estimated that there were 374 million new infections with one of four curable STIs: chlamydia, gonorrhea, syphilis, and trichomoniasis. Notably, approximately 8 million adults in this age group were infected with syphilis in 2022. Additionally, around 520 million people (13% of the population) are estimated to carry the herpes simplex virus type 2 (HSV-2), the primary cause of genital herpes. Human papillomavirus (HPV) is linked to over 311,000 cervical cancer deaths each year. Compounding these issues, 1.1 million pregnant women were estimated to be infected with syphilis in 2022, which resulted in over 390,000 adverse birth outcomes.
Overview of STIs
There are more than 30 different bacteria, viruses, and parasites that can be transmitted through sexual contact, including vaginal, anal, and oral sex. Some STIs can be passed from mother to child during pregnancy, childbirth, or breastfeeding. Of the numerous pathogens involved, eight are linked to the highest incidence rates of STIs: four of these are curable (syphilis, gonorrhea, chlamydia, and trichomoniasis), while the other four are viral (hepatitis B, herpes simplex virus, HIV, and human papillomavirus).
Emerging outbreaks of new infections, such as mpox, Shigella sonnei, Neisseria meningitidis, Ebola, and Zika—along with the re-emergence of neglected STIs like lymphogranuloma venereum—pose increasing challenges for adequate STI prevention and control services.
Scope of the Problem
The impact of STIs on sexual and reproductive health is significant. In 2020, the World Health Organization (WHO) estimated 374 million new infections, including 129 million cases of chlamydia, 82 million of gonorrhea, 7.1 million of syphilis, and 156 million of trichomoniasis. The prevalence of genital herpes in 2020 was estimated to be 520 million, with approximately 300 million women suffering from HPV infections, the leading cause of cervical and anal cancers.
Beyond the immediate effects of infections, STIs have serious long-term consequences. Conditions like herpes and gonorrhea can increase susceptibility to HIV. Mother-to-child transmission of STIs can lead to severe outcomes, including stillbirth or congenital deformities. Furthermore, HPV infection results in significant cancers, with 2022 figures showing hepatitis B led to around 1.1 million deaths from cirrhosis and liver cancer. Gonorrhea and chlamydia are major contributors to pelvic inflammatory disease and infertility.
Prevention of STIs
Condoms, when used correctly and consistently, are one of the most effective methods of protection against STIs, including HIV. However, they do not fully mitigate the risk for STIs that cause extra-genital ulcers, like syphilis and genital herpes. Ideally, condoms should be consistently used during all types of sex.
Vaccination is another powerful tool against certain STIs. Safe vaccines are available for hepatitis B and HPV. By the end of 2023, the HPV vaccine was introduced in 140 countries as a part of routine immunization, primarily in high- to middle-income nations. To mitigate cervical cancer as a public health issue globally, high vaccination coverage, alongside screening and treatment, must be achieved and maintained by 2030.
Research is also ongoing to create vaccines for genital herpes, with several candidates in early clinical stages. Studies suggest that the MenB vaccination might help protect against gonorrhea, underscoring the need for more research into effective vaccines for STIs like chlamydia, gonorrhea, syphilis, and trichomoniasis.
Other biomedical interventions include voluntary male circumcision, microbicides, and partner treatment. Trials are also underway to evaluate pre- and post-exposure prophylaxis for STIs while considering the threat of antimicrobial resistance (AMR).
Diagnosis of STIs
STIs often present with no symptoms, complicating diagnosis. When symptoms do occur, they can be vague and non-specific. Accurate diagnostic tests, particularly those using molecular technology, are widely utilized in high-income countries, especially for asymptomatic cases. However, such tests are often not available in low- and middle-income countries (LMICs) for conditions like chlamydia and gonorrhea. Testing is typically costly and inaccessible, leading to delays in treatment.
Rapid tests for syphilis, hepatitis B, and HIV are available and used in resource-limited settings, offering a glimmer of hope. Additional rapid tests are in development that could improve access to STI diagnosis and treatment globally.
Treatment of STIs
Effective treatments exist for several STIs. Chlamydia, gonorrhea, and syphilis are generally curable with single-dose antibiotic regimens, while antivirals can manage conditions like herpes and HIV, although they cannot cure them. For hepatitis B, antivirals help manage the virus and slow liver damage.
However, AMR, particularly concerning gonorrhea, has rapidly risen in recent years, limiting treatment options. The Gonococcal AMR Surveillance Programme (GASP) indicates alarming resistance to multiple antibiotics, complicating the treatment landscape.
STI Case Management
In low- and middle-income countries, STI management often relies on recognizing recognizable signs and symptoms, known as syndromic management. This method enables health workers to diagnose infections based on visible symptoms, which allows for rapid treatment. While this approach simplifies care in resource-limited settings, it can lead to overtreatment or missed diagnosis since most STIs are asymptomatic. WHO advocates for enhanced syndromic management through the gradual incorporation of laboratory testing, aiming to improve overall diagnostic accuracy.
Partner treatment is crucial to interrupt transmission and decrease the risk of re-infection, emphasizing the need for comprehensive STI case management.
Controlling the Spread
Behavior change surrounding STIs is complex. While education and counseling can improve awareness of STI symptoms, barriers like public stigma, lack of trained healthcare workers, and societal taboos often hinder the effectiveness of these interventions.
Many individuals seeking STI services encounter challenges, including limited healthcare resources, stigmatization, and poor-quality care. High-risk populations—such as sex workers, men who have sex with men, and adolescents—often lack access to friendly and responsive health services, underscoring the urgent need for comprehensive and inclusive STI care.
WHO Response
Guided by the Global Health Sector Strategy on HIV, Hepatitis, and STIs (2022–2030), WHO is committed to tackling the global burden of STIs. The organization develops targets, norms, and standards for STI management; supports economic assessments; monitors AMR; and fosters research agendas to stimulate advancements in diagnostics and vaccinations.
WHO also aids countries in creating national strategic plans, enhancing public discourse around STIs, and scaling up preventive measures, including making condom access more prolific. Ensuring that primary healthcare integrates STI services is crucial for improving care access while encouraging testing and treatment for at-risk populations.
Through these multifaceted efforts, WHO aims to address the complex landscape of STIs globally, emphasizing the importance of collaboration and resource allocation in enhancing health outcomes for all.
