Chlamydial infections are caused by bacteria. Transmission occurs through unprotected oral, vaginal or anal intercourse or during birth from the mother to the child. A chlamydial infection is treatable with antibiotics.

Pathogen and transmission

Chlamydial infections are caused by bacteria (Chlamydia trachomatis) and are the most frequently diagnosed sexually transmitted infections of bacterial origin. Transmission occurs through unprotected oral, vaginal or anal intercourse or during birth from the  mother to the child.

Clinical picture

About 70 % of women and 50 % of men with a chlamydial infection exhibit no or only minor symptoms. If symptoms do occur, they usually manifest within 2 to 6 weeks after infection, principally through stinging and pain during urination as well as through vaginal or urethral discharge. The infection can be transmitted to sexual partners even in the absence of symptoms. A chlamydial infection is treatable with antibiotics or may even heal spontaneously. In women, an untreated chlamydia infection can lead to pelvic inflammatory disease, which in turn occasionally causes abdominal pain, fever, abnormal discharge, pelvic pain or agglutination of the fallopian tubes, the latter of which increases the risk of ectopic pregnancy and sterility. In men, the consequence in rare cases is an epididymal inflammation with subsequent sterility. Infected newborns may come down with conjunctivitis or pneumonia.

Frequency and distribution

In Switzerland, as in the rest of Europe, the number of reported chlamydial infections per year has continuously increased since six years, with 11'013 new cases reported in 2016. Chlamydia affects an estimated 3 % - 10 % of the sexually active population, of which 70 % are women. The infection is common in adolescents and in young women below the age of 24; men are slightly older, on average, when diagnosed.


Condoms reduce the risk of getting infected with chlamydia. But an infection is possible despite condom use. It is important to detect and treat an infection early.


If you have changing or multiple sexual partners during the same time period, talk to your doctor or another specialist about sexually transmitted infections (including HIV) and get advice on whether tests may be necessary.

In case of an infection, provides tips on how to inform your partner.

And for everyone having sex:

Because everybody likes it differently: do the personalised Safer Sex Check at

Further Information

HIV & Sexually Transmitted Infections

The NPHS aims to reduce the number of new infections with HIV and other STIs and to avoid consequences with an adverse effect on health. Information on the programme can be found here.

Last modification 15.02.2022

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