Sexually transmitted infections (STIs)

Fact sheet N°110
Updated December 2015

Key facts

What are sexually transmitted infections and how are they transmitted?

More than 30 different bacteria, viruses and parasites are known to be transmitted through sexual contact. Eight of these pathogens are linked to the greatest incidence of sexually transmitted disease. Of these 8 infections, 4 are currently curable: syphilis, gonorrhoea, chlamydia and trichomoniasis. The other 4 are viral infections and are incurable: hepatitis B, herpes simplex virus (HSV or herpes), HIV, and human papillomavirus (HPV). Symptoms or disease due to the incurable viral infections can be reduced or modified through treatment.

STIs are spread predominantly by sexual contact, including vaginal, anal and oral sex. Some STIs can also be spread through non-sexual means such as via blood or blood products. Many STIs—including chlamydia, gonorrhoea, primarily hepatitis B, HIV, and syphilis—can also be transmitted from mother to child during pregnancy and childbirth.

A person can have an STI without having obvious symptoms of disease. Common symptoms of STIs include vaginal discharge, urethral discharge or burning in men, genital ulcers, and abdominal pain.

Scope of the problem

STIs have a profound impact on sexual and reproductive health worldwide.

More than 1 million STIs are acquired every day. Each year, there are estimated 357 million new infections with 1 of 4 STIs: chlamydia (131 million), gonorrhoea (78 million), syphilis (5.6 million) and trichomoniasis (143 million). More than 500 million people are living with genital HSV (herpes) infection. At any point in time, more than 290 million women have an HPV infection, one of the most common STIs.

STIs can have serious consequences beyond the immediate impact of the infection itself.

Prevention of STIs

Counselling and behavioural approaches

Counselling and behavioural interventions offer primary prevention against STIs (including HIV), as well as against unintended pregnancies. These include:

In addition, counselling can improve people’s ability to recognize the symptoms of STIs and increase the likelihood they will seek care or encourage a sexual partner to do so. Unfortunately, lack of public awareness, lack of training of health workers, and long-standing, widespread stigma around STIs remain barriers to greater and more effective use of these interventions.

Barrier methods

When used correctly and consistently, condoms offer one of the most effective methods of protection against STIs, including HIV. Female condoms are effective and safe, but are not used as widely by national programmes as male condoms.

Diagnosis of STIs

Accurate diagnostic tests for STIs are widely used in high-income countries. These are especially useful for the diagnosis of asymptomatic infections. However, in low- and middle-income countries, diagnostic tests are largely unavailable. Where testing is available, it is often expensive and geographically inaccessible; and patients often need to wait a long time (or need to return) to receive results. As a result, follow up can be impeded and care or treatment can be incomplete.

The only inexpensive, rapid tests currently available for STIs are for syphilis and HIV. The syphilis test is already in use in some resource-limited settings. The test is accurate, can provide results in 15 to 20 minutes, and is easy to use with minimal training. Rapid syphilis tests have been shown to increase the number of pregnant women tested for syphilis. However, increased efforts are still needed in most low- and middle-income countries to ensure that all pregnant women receive a syphilis test.

Several rapid tests for other STIs are under development and have the potential to improve STI diagnosis and treatment, especially in resource-limited settings.

Treatment of STIs

Effective treatment is currently available for several STIs.

Resistance of STIs—in particular gonorrhoea—to antibiotics has increased rapidly in recent years and has reduced treatment options. The emergence of decreased susceptibility of gonorrhoea to the “last line” treatment option (oral and injectable cephalosporins) together with antimicrobial resistance already shown to penicillins, sulphonamides, tetracyclines, quinolones and macrolides make gonorrhoea a multidrug-resistant organism. Antimicrobial resistance for other STIs, though less common, also exists, making prevention and prompt treatment critical.

STI case management

Low- and middle-income countries rely on identifying consistent, easily recognizable signs and symptoms to guide treatment, without the use of laboratory tests. This is called syndromic management. This approach, which often relies on clinical algorithms, allows health workers to diagnose a specific infection on the basis of observed syndromes (e.g., vaginal discharge, urethral discharge, genital ulcers, abdominal pain).

Syndromic management is simple, assures rapid, same-day treatment, and avoids expensive or unavailable diagnostic tests. However, this approach misses infections that do not demonstrate any syndromes - the majority of STIs globally.

Vaccines and other biomedical interventions

Safe and highly effective vaccines are available for 2 STIs: hepatitis B and HPV. These vaccines have represented major advances in STI prevention. The vaccine against hepatitis B is included in infant immunization programmes in 93% of countries and has already prevented an estimated 1.3 million deaths from chronic liver disease and cancer.

HPV vaccine is available as part of routine immunization programmes in 65 countries, most of them high- and middle-income. HPV vaccination could prevent the deaths of more than 4 million women over the next decade in low- and middle-income countries, where most cases of cervical cancer occur, if 70% vaccination coverage can be achieved.

Research to develop vaccines against herpes and HIV is advanced, with several vaccine candidates in early clinical development. Research into vaccines for chlamydia, gonorrhoea, syphilis and trichomoniasis is in earlier stages of development.

Other biomedical interventions to prevent some STIs include adult male circumcision and microbicides.

Current efforts to contain the spread of STIs are not sufficient

Behaviour change is complex

Despite considerable efforts to identify simple interventions that can reduce risky sexual behaviour, behaviour change remains a complex challenge. Research has demonstrated the need to focus on carefully defined populations, consult extensively with the identified target populations, and involve them in design, implementation and evaluation.

Health services for screening and treatment of STIs remain weak

People seeking screening and treatment for STIs face numerous problems. These include limited resources, stigmatization, poor quality of services, and little or no follow-up of sexual partners.

WHO response

WHO develops global norms and standards for STI treatment and prevention, strengthens systems for surveillance and monitoring, including those for drug-resistant gonorrhoea, and leads the setting of the global research agenda on STIs.

Our work is currently guided by the Global Strategy for the Prevention and Control of Sexually Transmitted Infections: 2006-2015, adopted by the World Health Assembly in 2006, and the 2015 United Nations Global Strategy for Women's, Children's and Adolescents’ Health, which highlight the need for a comprehensive, integrated package of essential interventions, including information and services for the prevention of HIV and other sexually transmitted infections. WHO is developing 3 new 2016-2021 Global Health Sector Strategies for HIV/AIDS, Viral Hepatitis, and STIs.

WHO works with countries to:

1. Newman L, Kamb M, Hawkes S, Gomez G, Say L, Seuc A, et al. (2013) Global Estimates of Syphilis in Pregnancy and Associated Adverse Outcomes: Analysis of Multinational Antenatal Surveillance Data. PLoS Med 10(2): e1001396. doi:10.1371/journal.pmed.1001396

2. International Agency for Research on Cancer: All Cancers (excluding non-melanoma skin cancer) Estimated Incidence, Mortality and Prevalence Worldwide in 2012 (http://globocan.iarc.fr/Pages/fact_sheets_cancer.aspx ). Accessed 8 December 2015.

Source: WHO - 09.12.2015