No 19/22b - 2026

Chlamydia 2025

• In 2025, the number of laboratory-confirmed chlamydia cases was 29,950.
• The number of testing episodes decreased by 6% from 2024 to 2025, while the number of chlamydia cases remained virtually unchanged.
• Males accounted for 45% of all detected chlamydia cases, while the positivity rate was higher among males (12.7%) than among females (7.2%).
• The incidence of chlamydia among young people aged 15–29 years was unchanged from 2024 to 2025.
• A total of 82% of all chlamydia cases occurred in the 15–29-year age group, unchanged from 2024.
• In 2025, males were tested to a considerably lesser extent than females: 3,470 testing episodes per 100,000 males compared with 7,491 testing episodes per 100,000 females.
• In 2019, doxycycline was recommended for the treatment of uncomplicated chlamydia. The reason for this was the high prevalence of azithromycin resistance among Mycoplasma (M.) genitalium in Denmark, presumably because azithromycin had until then been recommended as the standard treatment for uncomplicated chlamydia.
• Data from the Danish National Prescription Registry suggest that azithromycin is still used for the treatment of chlamydia in approximately 40% of cases. Its use should be reduced further.

As in previous years, the data used to prepare the 2025 chlamydia surveillance summary were obtained from the Danish Microbiology Database (MiBa) and include all positive and negative test results for oculo-genital infection caused by Chlamydia (C.) trachomatis. Throughout the 2025 report, figures from 2024 are presented for comparison. In 2024, the method used to retrieve chlamydia data from MiBa was revised and updated as part of a broader effort to standardise data extraction. The most important difference between the two methods is that, under the new method, individuals may have more than one negative testing episode during a calendar year, resulting in a higher number of testing episodes and consequently a lower positivity rate. A comparison of the two methods can be found in the full description of the occurrence of chlamydia in 2025.

A detailed epidemiological description of the occurrence of chlamydia in 2025 can be found here.

Since 2022, the number of testing episodes for chlamydia has decreased by 10%, while the number of detected chlamydia cases has decreased by 29%. The positivity rate has also declined from 11.3% in 2022 to 8.9% in 2025. During the most recent year, only very small changes in the occurrence of chlamydia have been observed.

With the exception of the age groups <1 year and 40+ years, more than twice as many females as males were tested for chlamydia in 2025. However, the positivity rate among males was higher than among females in almost all age groups. In 2025, males accounted for 45% of detected chlamydia cases, representing an increase of three percentage points since 2023.

A total of 82% of all chlamydia cases occurred among 15–29-year-olds. Among males in this age group, however, the number tested was substantially lower than among females. Preventive efforts should therefore be strengthened through information on safer sexual behaviour and partner notification following a diagnosis of chlamydia.

There is still no obvious explanation for the marked decline in the occurrence of chlamydia observed during the period 2022–2024.

For many years, azithromycin 1 g orally as a single dose was recommended in Denmark for the treatment of uncomplicated chlamydia. However, co-infection with C. trachomatis and M. genitalium is assumed to be relatively common, and because a substantially higher prevalence of azithromycin resistance among M. genitalium was found in Denmark than in Sweden, where doxycycline is used for the treatment of chlamydia, SSI decided in 2019, EPI-NEWS 38/2019, to change the treatment recommendation for chlamydia.

First-line treatment for uncomplicated chlamydia, including uncomplicated rectal chlamydia, subsequently became oral doxycycline 100 mg twice daily for seven days. For LGV in the rectum, the same dose is used for 21 days. Guidelines for the treatment of chlamydia in pregnancy and in persons with complicated chlamydia infections, including epididymitis and salpingitis, are available in the Danish Dermatological Society’s guidelines on Sexually Transmitted Infections.

(T.R. Pedersen, S. Hoffmann, Department of Bacteria, Parasites & Fungi)