Chlamydia is the most common STI and is caused by the bacterium Chlamydia trachomatis.

Symptoms

A large proportion of infections with chlamydia occur without symptoms, where 80% of infections in women and about half of infections in men are asymptomatic.

Symptoms depend on the location of the infection

• Urinary tract or vagina: pain when urinating, discharge from vagina or urethra, pain during intercourse, or blood loss after sexual contact
• Anus: itching, irritated skin, slimy or bloody discharge, or diarrhea 
• Throat: hardly ever occurs and almost never causes symptoms 

Diagnosis

Diagnosis is made by examination of a urine sample or a vaginal or anal swab. The swab is taken from the site where one experiences symptoms or where one had sexual contact.

Treatment and partner notification

Chlamydia infection is treated with antibiotics. It is recommended that recent sexual partners be notified so that they can also be tested and treated, if necessary. A check-up after treatment is not routinely required.

Transmission and prevention

The bacteria can be found in the mucus membranes of the vagina, anus, urethra and, in very rare cases, the throat. During sexual contact, the bacteria can be transmitted. The correct and consistent use of condoms is a safe and very effective way to prevent chlamydia.  

Possible complications

A chlamydia infection that is not treated can lead to pelvic inflammatory disease in women and, in the longer term, fertility problems and chronic pelvic pain. During delivery, chlamydia infection can be transmitted to the newborn, and cause eye infections.

Lymphogranuloma venereum

Lymphogranuloma venereum (LGV) is a special form caused by some subtypes (Serovar L1-3) of the bacterium Chlamydia trachomatis. This infection penetrates deeper into the tissues and therefore can cause a more severe syndrome, such as swelling of the genitals and lymph nodes. However, it is much less common. As a result of a deeper infection, longer treatment with antibiotics is required. It is also appropriate to check that the infection is completely healed after treatment. The correct and consistent use of condoms are a safe and very effective way to prevent LGV.  

Gonorrhea is caused by the bacterium Neisseria gonorrhoeae. 

Symptoms

Gonorrhea presents similar symptoms to chlamydia, but is more frequently symptomatic. A typical symptom is pus-like discharge, which is why gonorrhea is colloquially referred to as “the drip.” 

Symptoms depend on the location of the infection

• Urinary tract or vagina: pain when urinating, pus-like discharge from the vagina or urethra, pain during sexual intercourse, blood loss after sexual contact
• Anus: itching, irritated skin, mucus or bloody discharge and diarrhea 
• Throat: usually no symptoms, sometimes presents with sore throat or difficulty swallowing 

Diagnosis

Diagnosis is made by examination of a urine sample or swab. The swab is taken from the site where one experiences symptoms or where one had sexual contact.

Treatment and partner notification

A gonorrhea infection is treated with antibiotics. It is recommended that recent sexual partners be notified so that they can also be tested and treated, if necessary.

Transmission and prevention

The bacteria can be found in the mucus membranes of the vagina, anus, urethra and throat. During sexual contact, the bacteria can be transmitted. The correct and consistent use of condoms is a safe and very effective way to prevent gonorrhea.  

Possible complications

Untreated gonorrhea infection can lead to pelvic inflammatory disease in women and, in the long term, fertility problems and chronic pelvic pain. An untreated infection can also spread further through the blood. This can lead to joint and tendon inflammation, skin inflammation and, in rare cases, heart inflammation or meningitis.

During childbirth, gonorrhea infection can be transmitted to the newborn, and cause eye infections.

The bacterium that causes gonorrhea (Neisseria gonorrhoeae) is showing an increasing resistance to antibiotics. This is being closely monitored by the National Reference Center for STIs.

Syphilis is caused by the bacterium Treponema pallidum.

Symptoms

The bacterium can affect almost all organs. The typical course of a syphilis infection has several stages:

1. In the first stage, there is a painless ulcer on or around the penis, vagina, anus or mouth. After a few weeks to a few months, it heals on its own.
2. In the second stage, there is usually a pronounced, non-itchy rash on the trunk and extremities (including palms or soles of the feet) and wart-like bumps around the vagina or penis. Sometimes there can also be hair loss, fever and a general flu-like feeling.  
3. After the second stage, these symptoms often disappear. If syphilis is not treated, you can still get sick after several years without symptoms. The bacteria can then cause serious damage to the brain or heart.  

Diagnosis

Diagnosis is made with a blood test or by microscopic examination of tissue from an ulcer. A syphilis infection at the level of the brain is detected by lumbar puncture. 

Treatment and partner notification

A syphilis infection is treated with antibiotics; the dose depends on the stage of the disease. It is recommended that sexual partners of the past 12 months be notified so that they can also be tested and treated, if necessary.

Transmission and prevention

Infection occurs primarily during sexual contact (oral, vaginal, anal) or through direct contact with a lesion or skin rash. Condoms can partially protect against syphilis, on the condition that they cover all lesions. Pregnant women with syphilis may pass the infection to their baby during pregnancy or delivery. To prevent this, it is recommended that every pregnant woman be tested for syphilis.

Possible complications

An untreated infection can cause serious damage at the level of the brain and heart after several years.

If the infection is passed on during pregnancy, it can cause serious health problems for the baby, including a higher risk of death.

Genital herpes is caused by the herpes simplex virus (HSV). Cold sores, also known as fever blisters, are caused by a virus of the same family.

Symptoms

Small, painful vesicles filled with fluid at the level of the genital region. 

Diagnosis

Doctors can usually make the diagnosis based on symptoms. Sometimes, they take a sample of the vesicles to see if the virus is present.

Treatment

Genital herpes is not curable, but medications can reduce symptoms and flare-ups. 

Transmission and prevention

Genital herpes is highly contagious. The virus is transmitted primarily through direct contact with the vesicles. However, even when no vesicles are present, the virus can be passed on. Therefore, condoms offer only partial protection.

Possible complications

Pregnant women with the virus can infect their child if they have vesicles around the vagina at the time of delivery.

Genital warts are caused by the human papillomavirus (HPV). More than 100 different subtypes exist.

Symptoms

Warts often appear in groups and have a cauliflower-like surface. The warts may cause pain, itching or burning.

Diagnosis

A physician makes the diagnosis based on the presence of warts, also called lesions.

Transmission and prevention

Genital warts are highly contagious. In addition to sexual contact, one can become infected with the virus by touching genital warts or sharing a towel with a person who has genital warts. Therefore, condoms only partially protect against HPV. 

There is a vaccine against some HPV types, which can cause cancer as well as genital warts. It is included in the immunization schedule and is recommended for boys and girls aged 12 to 14 years.

Treatment

The majority of the population has already come into contact with HPV. The infection usually disappears on its own (it may take months or even years). If necessary, genital warts can be surgically removed or treated with a cream or laser. They can still return after treatment. In some people, warts can come back several times throughout their lives, while others get them only once.

Possible complications

Some types of human papillomavirus can give rise to cancer at the level of the cervix, anus, external genital organs and in the head-neck region. This is followed up by the Cancer Centre at Sciensano.

Hepatitis B, and in specific cases hepatitis C, is also an STI but this is followed up by specific surveillance. For more info, please visit this page.

HIV is also an STI but has its own surveillance network. For more info, please visit this page.