Any sexually active person can catch a sexually transmitted infection (STI). In addition to HIV/AIDS, there are other STIs. People with these infections often feel healthy and do not experience any symptoms. Fortunately, there are strategies to reduce the risk of infection: vaccination, prevention and treatment.

How are STIs transmitted?

Like many other infections, STIs can be transmitted through intimate and sexual contact, including anal, vaginal and oral sex, as well as shared use of sex toys. Transmission from mother to child can also occur during pregnancy, childbirth, or breastfeeding.

Description of the major STIs

Chlamydia

Cause: Bacterial infection.
Symptoms: Chlamydia often presents no symptoms. If symptoms do occur, the most common ones are pain during urination, pain or bleeding during sexual intercourse, intermenstrual bleeding, and unusual discharge from the vagina or penis.
Transmission: Chlamydia can be easily transmitted through all kinds of sexual contact; it is a very common infection.
Treatment: Antibiotics.
Note: If the infection is left untreated, there is a risk of Pelvic inflammatory disease (PID), ectopic pregnancy, or infertility.

Gonorrhoea

Cause: Bacterial infection.
Symptoms: Gonorrhoea often presents no symptoms. Typical symptoms that do occur include abdominal pain, pain during urination or sexual intercourse, intermenstrual bleeding, and unusual discharge from the vagina or penis.
Transmission: The infection is transmitted easily via various forms of sexual contact.
Treatment: Antibiotics.
Note: If the infection remains untreated, there is a risk of ectopic pregnancy or infertility.

Syphilis

Cause: Bacterial infection.
Symptoms: Symptoms can vary widely or go undetected. They develop in stages, starting with sores on the penis, in the anal area, or in the vagina or mouth, followed by a red rash on the body, palms of the hands, and soles of the feet.
Transmission: Syphilis can be transmitted through all kinds of sexual contact.
Treatment: Antibiotics.
Note: This infection is treatable in early stages, but untreated syphiliscan cause damage to the brain and other organs, which can be life-threatening.

Human papillomavirus (HPV)

Cause: Virus. There are different types of HPV.
Symptoms: In most cases, the virus does not cause any symptoms. Some strains can cause genital warts in the genital and anal area. Other strains can cause changes to the mucous membranes. In rare cases, these changes can develop into cancer (of the cervix, vagina, vulva, anus, penis or throat).
Transmission: Very common, through various types of sexual contact, including intimate contact without penetration.
Treatment: There are different treatments available depending on the type of problem.
Note: Vaccination offers the most effective protection. Vaccination is recommended for people aged 11 to 26, ideally prior to becoming sexually active. However, it is still effective for people who are already sexually active. The vaccination is free of charge.

Herpes

Cause: virus. There are two kinds of herpes virus.
Symptoms: Pimples in the mouth (cold sores, which are common and are not considered to be an STI), painful blisters or sores in the genital and anal area.
Transmission: Through direct contact with blisters or sores that contain the virus. Transmission is possible even if there are no symptoms. Most adults have already been infected with herpes without sexual contact. Oral-genital transmission is possible (e.g. contact between vulva and mouth or penis and mouth).
Treatment: Antiviral medications are available for severe symptoms.
Note: Herpes remains in the body throughout your life. An outbreak can occur at any time. The frequency of outbreaks varies from person to person.

Hepatitis

Cause: Virus. There are different types of hepatitis virus (such as A, B and C). The infection is called hepatitis because it causes inflammation of the liver.
Symptoms: Hepatitis often does not cause any symptoms. It can cause yellowing of the skin and eyes (jaundice), fever, vomiting, diarrhoea and loss of appetite.
The form of transmission differs depending on the type of virus:
Hepatitis A is transmitted through intimate contact between the mouth and anus (direct or via fingers).
Hepatitis B is transmitted through oral, anal and vaginal sex. It can be transmitted from mother to child at birth.
Hepatitis C is transmitted through blood-to-blood contact during specific sexual activities in which genital or anal injuries may occur or through the sharing of drug paraphernalia (needles, straws).
Treatment: Hepatitis A heals on its own. Hepatitis B can become chronic. Hepatitis B that has become chronic cannot be cured. However, transmission and liver damage (cirrhosis, cancer) can be prevented with medication. The hepatitis C virus can cause a chronic infection where there is a significant risk of developing liver cancer. Hepatitis C can usually be cured with antiviral medications.
Note: Vaccinations against hepatitis A and B are very effective and can prevent infection.

HIV/AIDS

Cause: Retrovirus.
Symptoms: In the first phase of infection (two to four weeks after transmission), flu-like symptoms can occur, such as fever, headache, sweating, joint pain and rashes. During this phase, the virus is easily transmitted between sexual partners. This phase often goes unnoticed, and the symptoms disappear quickly. After that, the virus does not cause any symptoms for a long time. However, it can still be transmitted, so it is important to get tested regularly. If the infection progresses and is not treated, it can lead to AIDS. AIDS can often be prevented by testing and treating the infection before symptoms appear.
Transmission: through anal or vaginal intercourse without a condom or without preventive treatment (PrEP). Transmission can also take place through the sharing of drug paraphernalia (needles).
Treatment: HIV is not curable, but there are treatments for it. People with HIV infections who are tested and treated remain healthy. Furthermore, treatment prevents the infection from being transmitted.

Note: There is no vaccine for HIV. The use of condoms during anal and vaginal sex is one of the most effective strategies to prevent HIV.
Emergency Treatment (PEP): Post-exposure prophylaxis (PEP) is available after high-risk exposure to HIV. The medication must be prescribed and started within 48 hours to be effective. PEP treatment lasts 28 days and requires medical supervision. Information and PEP are available at hospitals, sexual health centers, and checkpoints.
Preventive Treatment (PrEP): Pre-exposure prophylaxis (PrEP) is a highly effective treatment to prevent HIV infection. PrEP must be taken consistently as prescribed to maintain its effectiveness. It does not protect against other STIs. The treatment must be prescribed by a healthcare professional and is recommended for people at high risk of HIV exposure based on specified criteria.

When should I get tested for HIV and other STIs?

After anal or vaginal sex without a condom or during which the condom tore or slipped off.
At the beginning of a new sexually exclusive relationship.
For people not in a sexually exclusive relationship: once or several times a year, depending on the number of sexual partners.
If a sexual partner has tested positive for HIV or another STI.
If symptoms appear.

The same tests are not recommended for everyone. Seek advice from a specialist about your situation.

Where can I get tested and how much does it cost?

Testing can be carried out at test centers, sexual health centers, checkpoints, hospitals, and doctor’s offices. Testing methods include blood samples (from a vein or fingertip), swabs (vaginal, anal, urethral, or oral), or urine analysis, depending on the type of infection and sexual practices.

Tests are covered by health insurance providers if prescribed by a medical professional and the conditions of the insurance plan (e.g., deductible) are met. Some specialist centers offer anonymous tests at lower prices.

How can I reduce my STI risk?

You can get vaccinated against hepatitis A and B, HPV, and Mpox. This can reduce or even eliminate the risk of infection. Seek advice from a medical professional about which vaccinations you should get, if any.
Use a condom during penetrative anal, oral and vaginal sex. Using a condom greatly reduces the risk of HIV infection during anal or vaginal intercourse. Condoms also reduce the risk of transmission of other STIs.
Use each sex toy for one orifice only (anus, vagina, mouth). Apply a new condom to each sex toy for every new person or orifice. Also make sure to clean and disinfect your toys regularly.
Testing: Regular STI testing reduces the likelihood of transmission. Early detection allows infections to be treated promptly, preventing negative consequences. Seek advice on which tests are recommended based on your situation.
You can get more personalised recommendations by taking the Safer Sex Check at lovelife.ch.

Editing: 2024, SEXUAL HEALTH SWITZERLAND, Swiss foundation for sexual and reproductive health; ALECSS, Swiss association for sexual health experts in French- and Italian-speaking Switzerland for education, training and consultation; faseg, the professional association for sexual health in consultation and education.

Medical editing: Dr Vanessa Christinet

The content was created with financial support from the Federal Office of Public Health (BAG).

Sexually transmitted infections