Sexually Transmitted Infections (STIs)

Overview

More than 30 different bacteria, viruses, and parasites are known to be transmitted through sexual contact, including vaginal, anal, and oral sex. Some STDs can also be passed from mother to child during pregnancy, childbirth, and breastfeeding. Eight pathogens are associated with the highest rates of STDs. Of these, four are currently curable: syphilis, gonorrhea, chlamydia, and trichomoniasis. The other four are viral infections: hepatitis B, herpes simplex virus (HSV), HIV, and human papillomavirus (HPV).

In addition, new sexually transmissible infections such as MPOX are emerging. Shigella sonnei, Neisseria meningitidisThe emergence of new and emerging diseases such as Ebola, Zika, and neglected sexually transmitted infections, such as lymphogranuloma venereum, portends growing challenges in providing adequate sexually transmitted infection prevention and control services.

Problem Scope

Sexually transmitted infections have a profound impact on sexual and reproductive health worldwide.

Every day, more than 1 million cases of curable STIs are diagnosed. In 2020, WHO estimates there will be 374 million new infections with one of four STIs: chlamydia (129 million), gonorrhoea (82 million), syphilis (7.1 million), and trichomoniasis (156 million). In 2016, more than 490 million people were estimated to have genital herpes, and an estimated 300 million women were infected with HPV, the leading cause of cervical and anal cancers among men who have sex with men. In addition, updated WHO estimates By 2022, the number of hepatitis B patients will reach 254 million.

Sexually transmitted infections can have serious consequences beyond the direct effects of the infection itself.

• Sexually transmitted diseases such as herpes, gonorrhea, and syphilis can increase the risk of HIV infection.
• Mother-to-child transmission of STDs can result in stillbirth, neonatal death, low birth weight and preterm birth, sepsis, neonatal conjunctivitis, and congenital malformations.
• HPV infection can lead to cervical cancer and other cancers.
• In 2022, hepatitis B caused more than 1 million deaths, mostly from cirrhosis and hepatocellular carcinoma.
• Sexually transmitted infections such as gonorrhea and chlamydia are the leading causes of pelvic inflammatory disease and infertility in women.

Preventing Sexually Transmitted Infections

If used correctly and consistently, condoms are one of the most effective ways to prevent STIs, including HIV. Although condoms are very effective, they do not protect against STIs that cause extragenital ulcers (i.e., syphilis or genital herpes). If possible, condoms should be used during all vaginal and anal sex.

Safe and highly effective vaccines are available for two viral sexually transmitted infections, hepatitis B and HPV. These vaccines represent a major advance in the prevention of sexually transmitted infections. By the end of 2023, HPV vaccines had been introduced as part of routine immunization programs in 140 countries, primarily in high- and middle-income countries. To eliminate cervical cancer as a global public health problem, high coverage targets for HPV vaccination, screening and treatment of precancerous lesions, and cancer management must be achieved by 2030 and maintained at high levels for decades to come.

Progress has been made in developing a vaccine for genital herpes, with several candidates in early clinical development. There is growing evidence that the vaccine to prevent meningitis (MenB) provides some cross-protection against gonorrhea. More research is needed on vaccines for chlamydia, gonorrhea, syphilis, and trichomoniasis.

Other biomedical interventions for the prevention of some STIs include voluntary medical male circumcision of adults, microbicides, and partner therapy. Trials are underway to assess the benefits of pre- and post-exposure prophylaxis for STIs and their potential safety in relation to antimicrobial resistance (AMR).

Diagnosis of Sexually Transmitted Infections

STIs often have no symptoms. Even when symptoms occur, they may not be specific.

Accurate diagnostic tests for sexually transmitted infections (using molecular techniques) are widely used in high-income countries. These tests are particularly useful for diagnosing asymptomatic infections. However, testing for chlamydial infection and gonorrhoea is largely unavailable in low- and middle-income countries (LMICs). Even in countries where testing is available, it is often expensive and not widely available. In addition, the time it takes to get test results is often long. As a result, follow-up may be hampered and care or treatment may be incomplete.

On the other hand, rapid and inexpensive tests for syphilis, hepatitis B, and HIV already exist. Rapid syphilis tests and rapid HIV/syphilis dual tests are used in several resource-limited settings.

Several other rapid tests are in development that have the potential to improve diagnosis and treatment of STIs, particularly in resource-limited settings.

Treatment of sexually transmitted infections

Currently, effective treatments are available for many sexually transmitted infections.

• Three bacterial STDs (chlamydia, gonorrhea, and syphilis) and one parasitic STD (trichomoniasis) are usually curable with existing single-dose antibiotic therapies.
• For herpes and HIV, the most effective drugs are antiviral drugs, which can modulate the course of the disease but cannot cure it.
• For hepatitis B, antiviral medicines can help fight the virus and slow damage to the liver.

Drug resistance in sexually transmitted infections, particularly gonorrhea, has increased rapidly in recent years, reducing treatment options. Gonococcal Antimicrobial Resistance Surveillance Program (GASP) Shows high rates of resistance to multiple antibiotics, including quinolones, azithromycin, and broad-spectrum cephalosporins, a last-resort treatment (3).

Resistance to other sexually transmitted infections, such as Mycoplasma genitaliumalso exists, but is not monitored by the system.

Sexually Transmitted Infection Case Management

Low- and middle-income countries rely on the identification of consistent, easily recognizable signs and symptoms to guide treatment without the need for laboratory testing. This approach (syndromic management) often relies on clinical algorithms and allows health care providers to diagnose specific infections based on observed syndromes (e.g., vaginal/urethral discharge, anogenital ulcers, etc.). Syndrome Management Simple and easy to perform, it ensures rapid, same-day treatment and avoids expensive or inaccessible diagnostic testing for symptomatic patients. However, this approach can lead to overtreatment and underdiagnosis, as most STIs are asymptomatic. WHO therefore recommends that countries strengthen syndromic management by progressively incorporating laboratory testing to support diagnosis. In settings where quality-assured molecular testing methods are available, it is recommended that treatment for STIs be based on laboratory testing. In addition, STI screening strategies are essential for populations at higher risk of infection, such as sex workers, men who have sex with men, adolescents in certain settings, and pregnant women.

Treatment of sex partners is an important component of STI case management in order to interrupt transmission and prevent reinfection.

Controlling the spread

Behavior change is complex

Despite considerable efforts to identify simple interventions that can reduce risky sexual behaviors, behavior change remains a complex challenge.

Information, education, and counseling can improve people's ability to recognize symptoms of sexually transmitted infections, increasing the likelihood that they will seek treatment and encourage their sexual partners to seek treatment. Unfortunately, a lack of public awareness, poor training for health workers, and persistent and pervasive stigma surrounding sexually transmitted infections remain barriers to wider and more effective use of these interventions.

Health services for sexually transmitted infection screening and treatment remain weak

People seeking STI screening and treatment face many issues, including limited resources, stigma, poor quality of services, and frequent out-of-pocket costs.

Some of the populations with the highest rates of sexually transmitted infections – such as sex workers, men who have sex with men, people who inject drugs, prison inmates, migrant populations and adolescents in countries with a high HIV burden – often lack access to adequate and friendly health services.

In many settings, sexually transmitted infection services are often neglected and underfunded. These issues result in difficulties in providing testing for asymptomatic infections, insufficient numbers of trained personnel, limited laboratory capacity, and insufficient supplies of appropriate medicines.

WHO response

Our work is currently being Global health sector strategy for HIV, hepatitis and sexually transmitted infections 2022-2030. Within this framework, WHO:

• Setting global goals, norms and standards for sexually transmitted infection prevention, testing and treatment;
• Support assessment of the economic burden of sexually transmitted infections and strengthen sexually transmitted infection surveillance;
• Monitoring gonorrhoea drug resistance globally; and
• Leads the development of the global STI research agenda, including the development of diagnostic tests, vaccines, and other medicines for gonorrhea and syphilis.

As part of its mission, WHO supports countries to:

• Develop national strategic plans and guidelines;
• Create an encouraging environment where people can discuss STIs, practice safer sex, and seek treatment;
• Expanding primary prevention (availability and use of condoms, etc.);
• Strengthening the integration of sexually transmitted infection services into primary health care services;
• Improving access to quality, person-centred STI care;
• promoting the adoption of point-of-care diagnostic tests;
• Strengthen and scale up high-impact health interventions, such as hepatitis B and HPV vaccinations and syphilis screening for key populations;
• Strengthening capacity to monitor trends in sexually transmitted infections; and
• Surveillance and response to antimicrobial resistance in gonorrhea.

refer to

1. James C, Harfouche M, Welton NJ, et al. Herpes simplex virus: global prevalence and incidence estimates of infection, 2016. Bulletin of the World Health Organization. 2020;98(5):315-329.
2. Bray F, Ferlay J, Soerjomataram I, Siegel RL, Torre LA, Jemal A. World cancer statistics 2018: GLOBOCAN estimates of global incidence and mortality for 36 cancers in 185 countries. CA Cancer J Clin. 2018 Nov;68(6):394-424. Epub 2018 Sep 12. Errata: CA Cancer J Clin. 2020 Jul;70(4):313.
3. Unemo M, Lahra MM, Escher M, Eremin S, Cole MJ, Galarza P, Ndowa F, Martin I, Dillon JR, Galas M, Ramon-Pardo P, Weinstock H, Wi T. WHO Global Antimicrobial Resistance Surveillance of Neisseria gonorrhoeae (GASP/GLASS) 2017–2018: a retrospective observational study. Lancet Microbiol 2021;2:e627–36