No 23/26 - 2025

Chlamydia 2024

• In 2024, the number of laboratory-confirmed chlamydia cases was 29,946.
• The number of examination episodes fell by 7% from 2023 to 2024, and the number of chlamydia cases decreased by 19%.
• Men made up 44% of all confirmed chlamydia cases, while the positivity rate was higher among men (12%) than among women (7%).
• The incidence of chlamydia among young people aged 15–29 continued to decline from 2023 to 2024.
• 82% of all chlamydia cases occurred in the 15–29 age group, which is a decrease of 4 percentage points from 2023.
• In 2024, men were tested significantly less than women: 3,683 examination episodes per 100,000 men versus 7,979 examination episodes per 100,000 women.
• 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 until then had been recommended as standard treatment of uncomplicated chlamydia.
• Extracts from The Danish National Prescription Registry suggest that azithromycin is still used to treat chlamydia in about half of the cases. The usage should be further reduced.

As in previous years, data for the preparation of the chlamydia report for 2024 were obtained via the Danish Microbiology Database (MiBa) and include all positive and negative test results for oculo-genital infection caused by Chlamydia (C.) trachomatis. In the report for 2024, figures from 2023 are presented in several places for comparison. In 2024, the method by which data regarding chlamydia is retrieved from MiBa was revised and updated as part of a larger effort for standardized data extraction, with the greatest difference between the two methods being that individuals may have more than one negative sampling episode annually, which results in more examination episodes and thereby significantly affects positivity rates from earlier reports.

A detailed epidemiological description of the incidence of chlamydia in 2024 can be read here.

Since 2022, the number of examination episodes for chlamydia has decreased by 4%, and the number of confirmed chlamydia cases has decreased by 28%. The positivity rate has also decreased by 2.8 percentage points to 8.5%.

Except for the age groups < 1 year and 40+ years, more than twice as many women as men were tested for chlamydia. However, the positivity rate among men was higher than among women in almost all age groups. In 2024, men accounted for 44% of confirmed chlamydia cases, which is an increase of 2 percentage points since 2023.

A total of 82% of all chlamydia cases occur in 15–29-year-olds. Among men in this age group, however, the number of individuals tested is significantly lower than among women, which is why the prevention effort should be strengthened with information about safe sexual behavior, as well as partner notification in case of confirmed chlamydia.

There is no obvious explanation for the very significant decrease in chlamydia incidence. A sudden increase in condom use seems implausible. A theoretical possibility is a reduced tendency to have rapidly changing sexual partners, but there is no data to support or refute this.

Previously, azithromycin 1g orally as a single dose was recommended in Denmark for many years for the treatment of uncomplicated chlamydia. However, co-infection with C. trachomatis and M. genitalium is assumed to be relatively common, and since a significantly higher prevalence of azithromycin resistance among M. genitalium was found in Denmark compared to Sweden, where doxycycline is used to treat chlamydia, it was decided at SSI in 2019, EPI-NEWS 38/2019, to change the recommendation for chlamydia treatment. First-line treatment of uncomplicated chlamydia, including uncomplicated rectal chlamydia, was thereafter oral doxycycline 100 mg twice daily for seven days. For LGV in the rectum, the same dose is used, but for 21 days. Guidelines for the treatment of chlamydia in pregnant women and in persons with complicated chlamydia cases, including epididymitis and salpingitis, can be found in the Danish Dermatological Society’s guidelines on Sexually Transmitted Infections.

(T.R. Pedersen, S. Hoffmann, Department for Bacteria, Parasites & Fungi, L. Nielsen, Data Integration and Analysis)