Chlamydia 2024
Chlamydia – Summary of Disease Incidence 2024
Data from the Danish Microbiology Database
As in previous years, data for the preparation of this present report for 2024 has been obtained via the Danish Microbiology Database (MiBa). Data includes all positive and negative test results for oculo-genital infection caused by Chlamydia (C.) trachomatis from all clinical microbiology departments (DCMs). Data includes personal ID numbers, making it possible to delimit disease episodes at the individual level. A new disease episode is defined by there being more than 42 days between two sampling episodes with positive results. For patients with a valid personal ID number, information on municipality code and thereby region and area are retrieved from the CPR register.
In the report, several figures from 2023 are stated, taken from the previous year’s summary, for comparison. In 2024, the method by which data on chlamydia is obtained from MiBa was revised and updated as part of a broader effort toward standardized data extraction. The main difference between the two methods is that individuals may have more than one negative sampling episode per year, which leads to more examination episodes and thus significantly affects positivity rates from reports prior to 2023. In this present report, the number of examination episodes from 2015 to 2024 is provided.
Other Data
Chlamydia testing is also performed in an unknown scope by private laboratories. Such data are not included in this report. In the case of finding chlamydia in the rectum or suspected lymphogranuloma venereum (LGV), EPI-NEWS 20/2008, some DCMs and venereal disease clinics submit material to Statens Serum Institut (SSI) for special testing for LGV.
Chlamydia Incidence
In 2024, 277,862 persons (191,209 women, 86,441 men and 212 of unknown gender) were tested for chlamydia, across 352,378 examination episodes, Table 1, which is a decrease from 295,346 tested persons and 380,618 examination episodes in 2023. The number of confirmed cases was 29,946 in 2024, a decrease of 19% from 2023, where 37,111 cases were observed. Since 2022, a steady decline in positivity rate has been observed from 11.3% in 2022 to 9.8% in 2023 and now the lowest in the past 10 years: 8.5% in 2024. Not all tested individuals have information on both gender, age, and region, which is why different positivity rates may occur in the following tables.
Table 2 is divided by gender and shows the number of chlamydia cases and incidence rate per 10⁵ inhabitants. The largest decrease is seen in the age group 15–29 years for both men and women.
Additionally, a significant decrease was seen among women aged 10–14 years. Among women, the incidence rate dropped in all age groups, most in the younger age groups and least among 35–39-year-olds and 45–49-year-olds. Overall, the incidence rate among women fell from 712 per 105 inhabitants to 556 per 10⁵, corresponding to a 22% decline. Among men, the greatest decrease was among 15–24-year-olds, and a decline was seen in all age groups except 35–39 and 45–49, where a small increase was observed. Overall among men, the incidence rate dropped from 533 to 444 per 105 inhabitants, a 17% decrease.
Among 15–29-year-olds, the incidence rate of confirmed chlamydia cases fell significantly from 2023 to 2024, Figure 1. This large decline was observed across all 1-year age groups and both genders, resulting in the lowest incidence rates in recent years. The lowest incidence rate among women was seen in 19-year-olds, which was also the case in 2023. Among men, the lowest incidence was in 20-year-olds, whereas in 2023 it was 21-year-olds. In 2024, 87% of all confirmed chlamydia cases among women were in the 15–29 age group, and 75% for men. In total, 82% of all confirmed cases were among 15–29-year-olds. In 2024, cases among men constituted 44% of all cases, a rise of two percentage points from 2023.
Geographical Distribution
From 2023 to 2024, a drop in incidence rate per 105 inhabitants was seen across all provinces for both men and women, Table 3. The largest drop among women was in East Zealand (32%), and among men in North Jutland (24%). The smallest drop for both genders was in Funen (14% for women, 12% for men). Copenhagen City was the only province where men had a higher incidence rate than women. The lowest male/female incidence ratio was in West Jutland (0.66), whereas in 2023 it was East Zealand (0.63). The greatest increase in M/F incidence ratio was in East Zealand, rising from 0.63 in 2023 to 0.79 in 2024. Only in Copenhagen Suburbs and West Jutland did the M/F incidence ratio fall. There was a continued increase in the national M/F incidence ratio from 0.75 in 2023 to 0.80 in 2024, Table 3.
Diagnostics
Among persons with confirmed chlamydia, 90% were examined by general practitioners or specialists and 10% by hospital departments, virtually the same as in 2023.
Chlamydia in Children
Chlamydia was confirmed in children in 82 cases in 2024 (135 in 2023), of which 57 were among 1–14-year-olds (90 in 2023) and 25 among 0-year-olds (45 in 2023). Among 10–14-year-olds, 54 of the 57 cases were in girls (82 in 2023) and 3three in boys (7seven in 2023). All 25 cases among 0-year-olds were positive eye swabs, underlining the importance of remembering chlamydial infections as a cause of conjunctivitis in newborns.
Testing Frequency by Age and Gender
From 2023 to 2024, a general decrease in incidence rate of chlamydia testing was observed, Table 4. However, a slight increase in testing incidence was seen among men aged 35+. The largest decrease was among 10–24-year-olds for both genders, also with a simultaneous drop in positivity rate, indicating a real decline in the number of infected individuals. Thus, the drop in testing incidence is not necessarily unfortunate. Testing incidence fell by 5% for men and 9% for women. The positivity rate decreased overall from 2023 to 2024 for both genders, with the largest drop in younger age groups despite lower testing incidence, Table 4.
Chlamydia Treatment
In 2019, EPI-NEWS 38/2019, it was recommended to use doxycycline instead of azithromycin for treatment of uncomplicated chlamydia. The reason was high azithromycin resistance among Mycoplasma genitalium in Denmark, compared to Sweden, where doxycycline is standard treatment.
Data from The Danish National Prescription Registry suggests azithromycin use has decreased, but still accounts for about 60% of treatments in 2024. Usage should be further reduced.
In 2024, a drop was seen in the number of positive urogenital and throat chlamydia tests for both men and women, Table 5. The number of rectal samples from women testing positive declined from 2023 to 2024. For men, comparison is harder, as rectal samples are sometimes analyzed together with samples from other anatomical locations, making it impossible to tell whether positivity was in the rectum or another site, Table 5.
Chlamydia Testing and Positivity by Province and Gender
Overall, a decrease in incidence rate for chlamydia testing was seen across all provinces and both genders from 2023 to 2024, Table 6. A decrease in positivity rate was observed everywhere, with the largest drop in Jutland among men. For women, the biggest fall was also in Jutland and East Zealand. The highest testing incidence was again in 2024 in Copenhagen City for both men and women, and the lowest again in Bornholm. Despite the large drop in positivity, West Jutland still had the highest positivity rate for both men and women (16.5% and 9.4%, respectively), as was also the case in 2023.
Chlamydia Rectal Testing in Men
From 2023 to 2024, an increase in the number of testing episodes and positivity rate was seen, while the number of cases slightly declined, Table 7. The table includes both rectal samples and those analyzed with samples from other anatomical sites, often throat swabs. An increase in testing was seen in all provinces except Copenhagen Suburbs, where testing numbers were unchanged. The number of confirmed cases dropped from 1,313 in 2023 to 1,271 in 2024, with the largest decline in the Capital Region of Denmark. In the Region of Southern Denmark, especially in the province of Funen, the number of rectal chlamydia cases among men rose significantly from 2023 to 2024. Nationally, the positivity rate fell from 7.6% (2023) to 6.9% (2024). Funen and South Jutland were the only provinces with a rising positivity rate, especially Funen, from 3.4% (2023) to 6.2% (2024).
Lymphogranuloma Venereum (LGV)
At SSI, specific LGV testing with nucleic acid amplification technique (NAT) was conducted on 1,597 samples in 2024. These came from 1,406 individuals: 1,168 men, 233 women, and 5 of unknown gender. This showed a decrease compared to 2023, when 1,826 samples from 1,561 individuals were tested. The largest decrease in number of tests was among women, where LGV is rare. For both genders, LGV was most often tested anorectally, and in some cases from throat or urogenitally. Despite the decrease in tests, the number of confirmed LGV cases increased significantly from 2023 (100 samples across 94 episodes) to 2024 (140 samples across 135 episodes). Nationally, the number of LGV tests fell by 13%, but the number of confirmed LGV episodes rose by 44% (from 94 in 2023 to 135 in 2024).
This summary is also mentioned in EPI-NEWS 23–26/2025.