Sexually transmitted infections (STIs)
- 499 million new infections of curable sexually transmitted (syphilis, gonorrhoea, chlamydia and trichomoniasis) infections occur yearly.
- Some sexually transmitted infections exist without symptoms.
- In pregnant women with untreated early syphilis, 21% of pregnancies result in stillbirth and 9% in neonatal death.
- Sexually transmitted infections are an important cause of infertility in men and women.
- Drug resistance, especially for gonorrhoea, is a major threat to STI control globally.
- STIs can increase the risk of HIV acquisition three-fold or more.
Sexually transmitted infections (STIs) are a public health issue
Sexually transmitted infections have a major negative impact on sexual and reproductive health worldwide. Of the more than 30 identified pathogens known to be transmitted sexually, eight have been linked to the greatest incidence of illness. Four of these are currently curable (the bacterial infections syphilis, gonorrhoea, and chlamydia, and the protozoal infection trichomoniasis). Four viral infections are incurable, though modifiable with treatment: human immunodeficiency virus (HIV), human papillomavirus (HPV), herpes simplex virus (HSV), and hepatitis B virus (HBV). Hepatitis B and some types of HPV are vaccine-preventable infections.
According to 2008 WHO estimates, 499 million new cases of curable STIs (syphilis, gonorrhoea, chlamydia and trichomoniasis) occur annually throughout the world in adults aged 15-49 years. These figures do not include the additional health burden caused by HIV and other viral STIs such as HSV. Unlike other conditions such as unintended pregnancy or HIV infections, for example, which disproportionately affect sub-Saharan African and South East Asian countries, STIs are a public health problem in all countries. In developing countries, STIs and their complications rank in the top five disease categories for which adults seek health care. In addition, antimicrobial resistance, in particular for gonorrhoea, is becoming increasingly widespread.
Infections and transmission
STIs are infections that are spread primarily through person-to-person sexual contact. HIV and syphilis can also be transmitted from mother to child during pregnancy and childbirth, and through blood products and tissue transfer.
STIs are caused by bacteria, viruses and parasites. Some of the most common infections are below.
Common bacterial infections
- Neisseria gonorrhoeae (causes gonorrhoea or gonococcal infection)
- Chlamydia trachomatis (causes chlamydial infections)
- Treponema pallidum (causes syphilis)
- Haemophilus ducreyi (causes chancroid)
- Klebsiella granulomatis (previously known as Calymmatobacterium granulomatis causes granuloma inguinale or donovanosis).
Common viral infections
- Human immunodeficiency virus (causes AIDS)
- Herpes simplex virus 1 and type 2 (causes genital herpes)
- Human papillomavirus (causes genital warts and certain subtypes lead to cervical cancer in women)
- Hepatitis B virus (causes hepatitis and chronic cases may lead to cancer of the liver)
- Trichomonas vaginalis (causes vaginal trichomoniasis)
STIs adversely affect the health of women
Untreated STIs can have critical implications for reproductive, maternal and newborn health. STIs are an important preventable cause of infertility for men and women.
For example, 10–15% of women with untreated chlamydial infection may develop symptomatic pelvic inflammatory disease (PID), and about 10–15% of clinical PID cases lead to tubal factor infertility. Given that approximately 95.5 million women are infected with gonorrhoea or chlamydia each year, the numbers of women with adverse reproductive outcomes could be sizeable. In the United States, the proportion of infertility that is tubal factor ranges from 10–40%, whereas in sub-Saharan Africa untreated genital infection may be the cause of up to 85% of infertility among women seeking infertility care.
Furthermore, women who have had pelvic inflammatory disease may be 6–10 times more likely to develop an ectopic (tubal) pregnancy than those who have not, and 40–50% of ectopic pregnancies can be attributed to previous pelvic inflammatory disease.
Infection with certain types of the human papillomavirus can lead to the development of genital cancers, particularly cervical cancer in women. Worldwide, HPV infection results in 530 000 cases of cervical cancer and 275 000 cervical cancer deaths each year; 88% of these deaths occur in low- and middle-income countries where there is little or no access to cervical cancer screening and treatment.
STIs and adverse outcomes of pregnancy
Untreated STIs are associated with congenital and perinatal infections in neonates, particularly in regions where rates of infection remain high. All of the curable STIs have been linked with preterm labor, with associated risks to the neonate of pre-term birth, low birth weight, and death.
In 2008, it was estimated that over 1.3 million cases of syphilis occurred globally among pregnant women, and that a large proportion of these were untreated or inadequately treated. Unless testing and treatment of syphilis in pregnancy are universally available, over half of pregnancies in women with syphilis will result in an adverse outcome. An estimated 520 000 cases resulted in adverse outcomes, including 305 000 stillbirths and neonatal deaths, that could have been averted with universal access to testing and treatment.
In the absence of prophylaxis, 30–50% of infants born to mothers with untreated gonorrhoea and up to 30% of infants born to mothers with untreated chlamydial infection will develop a serious eye infection (ophthalmia neonatorum), which can lead to blindness if not treated early. Worldwide it is estimated that 1000–4000 newborn babies become blind every year because of this condition. Pneumonia can occur in up to 10–20% of infants born to a mother with untreated chlamydial infection.
Perinatal transmission of HSV-1 and 2 infection is associated with a high risk of long-term neurological problems and death, though global data are lacking on burden of disease. Hepatitis B infection can also be transmitted from mother to child at birth, which can lead to chronic infection and cancer.
STIs and HIV
The presence of untreated STIs (both those which cause ulcers or those which do not) increase the risk of both acquisition and transmission of HIV, by a factor of up to two- to three-fold. Prompt treatment for STIs is thus important to reduce the risk of HIV infection. Controlling STIs is important for preventing HIV infection, particularly in people with high-risk sexual behaviours.
Although many different pathogens cause STIs, some display similar or overlapping signs (what the individual or the health-care provider sees on examination) and symptoms (what the patient feels such as pain or irritation). Some of these signs and symptoms are easily recognizable and consistent, giving what is known as a syndrome that signals the presence of one or a number of pathogens. For example, a discharge from the urethra in men can be caused by gonorrhoea alone, chlamydia alone or both together.
The main syndromes of common STIs are:
- urethral discharge
- genital ulcers
- inguinal swellings (bubo, which is a swelling in the groin)
- scrotal swelling
- vaginal discharge
- lower abdominal pain
- neonatal eye infections (conjunctivitis of the newborn).
Some STIs exist without symptoms. For example, the vast majority of women and a significant proportion of men with chlamydial and/or gonococcal infections experience no symptoms at all. Both symptomatic and asymptomatic infections can lead to the development of serious complications.
STI syndromic approach to patient management
The most accurate method of diagnosing STIs is by laboratory tests, but these are often unavailable or too expensive, especially outside of developed countries. Because of this, since 1990 WHO has recommended a syndromic approach to diagnosis and management of STIs in patients presenting with consistently recognized signs and symptoms of particular STIs. However, current syndromic management algorithms do not perform well for some syndromes and do not address the much larger burden of asymptomatic STIs.
Therefore, one of the most urgent needs for STI control and prevention in the developing world is rapid, low-cost, and accurate point-of-care diagnostic tests, such as those currently available for syphilis testing.
STI drug resistance
Resistance of gonorrhoea to antibiotics, has increased rapidly in recent years and has reduced the options for treatment. The emergence of decreased susceptibility of N. gonorrhoeae to the “last line” treatment option of oral and parenteral cephalosporins together with antimicrobial resistance already shown to penicillins, sulphonamides, tetracyclines, quinolones and macrolides make N. gonorrhoeae a multidrug-resistant organism. Gonorrhoea represents 106 million of the estimated 499 million new cases of curable STIs which occur globally every year.
The most effective means to avoid becoming infected with or transmitting a sexually transmitted infection is to abstain from sexual intercourse (i.e. oral, vaginal, or anal sex) or to have sexual intercourse only within a long-term, mutually monogamous relationship with an uninfected partner. Male latex condoms and female condoms, when used consistently and correctly, are highly effective in reducing the transmission of HIV and other sexually transmitted infections, including gonorrhoea, chlamydial infection and trichomoniasis, in addition to preventing pregnancy.
Behaviour change interventions are an essential part of comprehensive STI/HIV prevention. Prevention as a combination approach should include structural changes and access to commodities (e.g. condoms, information) and services (e.g. testing, treatment and care) within a human rights framework. Over the last decade, substantial research has been undertaken to develop evidence-based interventions that promote safer sexual behaviours (e.g. delay in sexual debut, consistent condom use, reduction in number of partners, and seeking of HIV/STI testing) as well as sexual well-being through increased self-esteem, self-regulation, and a positive attitude towards one’s own as well as others’ sexuality.
Vaccination for viral STIs
Safe and highly effective vaccines against hepatitis B virus (HBV) and human papillomavirus (HPV) have been major advances in STI prevention.
HBV vaccine, the first STI vaccine developed, has been adopted into infant immunization programs in 93% of countries and has already prevented an estimated 1.3 million deaths from chronic liver disease and cancer.
HPV vaccine has been available since 2007 as part of routine immunization programmes in over 50 mostly high- and middle-income countries. HPV vaccination could prevent the death of more than 4 million women over the next decade in low- and middle-income countries if 70% vaccination coverage can be achieved.
Prevention of mother-to-child transmission of STIs
Most countries have antenatal syphilis screening policies in place but implementation needs to be strengthened; for example, only about 30% of pregnant women with syphilis in sub-Saharan Africa receive testing and treatment. Renewed efforts are needed to ensure scale-up of syphilis testing and treatment for all pregnant women in high-burden countries. New accurate point-of-care diagnostic tests for syphilis make syphilis screening of antenatal and high-risk populations feasible, even in remote settings. Universal screening and treatment for syphilis in pregnancy could prevent 492 000 syphilis-related stillbirths and perinatal deaths in sub-Saharan Africa alone.
A combination of prophylaxis against eye infection and improved detection and treatment of gonorrhoea and chlamydia in pregnancy can reduce infection-related blindness in the newborn and serious postpartum pelvic infections in women. Unfortunately rapid, low-cost, and accurate point-of-care diagnostics are not yet available for gonorrhoea or chlamydia.
The control of STIs is a priority for WHO. The World Health Assembly endorsed the global strategy for the prevention and control of STIs in May 2006. More recently, the United Nations Secretary-General’s Global Strategy for Women's and Children's Health highlighted the need for a comprehensive, integrated package of essential interventions and services. The Strategy urges partners to ensure that women and children have access to a universal package of guaranteed benefits, including family-planning information and services, antenatal, newborn and postnatal care, emergency obstetric and newborn care and the prevention of HIV and other sexually transmitted infections. Such a package could accelerate the response towards meeting health-related Millennium Development Goals.
WHO has identified the following key points for action.
- Scale-up of effective STI services:
- STI case management and counseling
- syphilis testing and treatment
- delivery of HPV and HBV vaccination.
- Promotion of strategies to enhance STI-prevention impact:
- integration of STI services into existing health systems
- advocacy to fight stigma against STIs
- STI prevention through sexual health promotion
- measurement of STI burden.
- Support for new technology development for STI prevention:
- point-of care diagnostic tests for STIs
- additional drugs for gonorrhoea
- STI vaccines and other biomedical interventions.
For more information contact:
WHO Media Centre
Telephone: +41 22 791 2222