Chlamydia 2023
Chlamydia - Report on Disease Incidence 2023
Data from the Danish Microbiology Database
As in previous years, data for the preparation of this report for 2023 was obtained via the Danish Microbiology Database (MiBa). The data includes all positive and negative test results for oculo-genital infection caused by Chlamydia (C.) trachomatis from all clinical microbiology departments (KMAs). The data includes personal identification numbers, allowing disease episodes to be delineated at the individual level. A new disease episode is defined as having more than 42 days between two sampling episodes with positive results. For patients with a valid personal identification number, information on municipality CODE and thus county and region was obtained from the civil registration system (CPR).
In this report for 2023, figures from 2022 are provided for comparison in several places. In 2024, the method by which data on chlamydia is collected from MiBa was revised and updated as part of a larger effort for standardized data extraction, with the main difference between the two methods being that individuals can have more than one negative sampling episode annually, which results in more testing episodes and thus significantly affects positivity rates from previous reports. This also leads to small differences between the figures for 2022 in this report and the figures in the annual report for 2022. In this report, the number of testing episodes from 2014 to 2023 is provided.
Other Data
Chlamydia testing is also conducted to an unknown extent in private laboratories. Such data is not included in this report. In cases of chlamydia found in the rectum or suspected lymphogranuloma venereum (LGV), EPI-NEWS 20/2008, some KMAs and venereal clinics send material to Statens Serum Institut (SSI) for special testing for LGV.
Chlamydia Incidence
In 2023, 295,346 people (204,700 women, 90,484 men, and 162 of unknown gender) were tested for chlamydia, distributed over 380,618 testing episodes, which is a slight increase from 286,839 tested individuals and 368,645 testing episodes in 2022. The increase in testing episodes is, as noted, influenced by changed definitions for surveillance purposes. The number of confirmed cases in 2023 was 37,111, a decrease of 10.8% from 2022, where 41,595 cases were observed, as shown in Table 1. Information regarding gender, age, and region is not available for all tested individuals, which is why different positivity rates may occur in the following tables.
Table 2 is divided by sex and shows the distribution by age groups of the number of chlamydia cases and incidence rate per 105 inhabitants. The incidence rate decreased for the 15-29 age group for both genders, whereas a slight increase was seen among men aged 30-34 and 50+.
Among women, a slight decrease in incidence rate was observed for the 30-39 age group and an increase among girls aged 10-14. Overall, there was a decrease in incidence rate for both men (from 591 to 533) and women (from 820 to 712) from 2022 to 2023. The majority of cases were seen among the 15-29 age group, which in 2023 accounted for 84% of all cases, 88% for women and 78% for men. This shows a decrease in the proportion of cases for men in this age group, which was 81% in 2022. In 2023, cases among men accounted for 42% of all cases, which was also the case in 2022.
Among the 15-29 age group, the incidence rate of confirmed chlamydia cases decreased from 2022 to 2023 for both genders and all 1-year age groups except for 29-year-old men. The highest incidence rate among women was seen in 19-year-olds (6,694 cases per 105) and among men in 21-year-olds (3,831 cases per 105). The largest decrease in incidence rate of confirmed chlamydia cases was seen among the 16-23 age group, Figure 1.
Geographical Distribution
From 2022 to 2023, the incidence rate of laboratory-confirmed chlamydia cases (per 105 inhabitants) decreased for both men and women across the entire country, except for men on Bornholm, Table 3. A larger decrease in incidence rate was observed in the Capital Region of Denmark for both sexes. For women, a significant decrease in incidence rate was seen in North, West, and East Jutland. The male/female incidence ratio (MFIR) was 0.75 nationwide in 2023 (2022: 0.72). Most notably, an increase in MFIR was observed in the Capital Region of Denmark.
Diagnostics
Among patients with confirmed chlamydia, 91% were examined by general practitioners or specialists and 9% by hospital departments, as in 2022.
Chlamydia in Children
Chlamydia was detected in 135 cases in children in 2023 (126 in 2022), of which 90 cases were among 1-14-year-olds (72 in 2022). In the 10-14 age group, the number of confirmed chlamydia cases was seven among boys (seven in 2022) and 82 among girls (64 in 2022). The figures for 2022 and 2023 are shown in Table 2. Among the 45 infants in 2023, more than 95% were positive in eye swabs, highlighting the importance of considering chlamydia infections as a cause of conjunctivitis in newborns.
Testing Frequency by Age Groups and Gender
From 2022 to 2023, a general increase in the incidence rate of chlamydia testing was observed, except for a slight decrease among the 15-24 age group for both genders. In 2023, men were tested significantly less than women for chlamydia, with 3,892 tests per 100,000 compared to 8,818 tests per 100,000. This is true for the age group 1-49 years, whereas men are tested more in the age groups <1 year and 50+. The same pattern in testing frequency was seen in 2022. The highest incidence rate of testing was observed among the 20-24 age group for both genders, with 15,215 tests per 105 for men and 42,589 tests per 105 for women.
For both genders, a decrease in positivity rate was observed from 2022 to 2023, from 9.4% to 8.1% for women and from 15.8% to 13.7% for men, which is seen in all age groups except men 50+ and girls aged 10-14. The largest decrease in positivity rate was seen among 15-19-year-old men despite the lower incidence rate of chlamydia testing. The highest positivity rate was observed among the 15-19 age group for both sex, 27.9% for men and 18% for women.
Treatment of Chlamydia
In 2019 (EPI-NEWS 38/2019), it was recommended to use doxycycline instead of azithromycin for the treatment of uncomplicated chlamydia. The reason for this was the high prevalence of azithromycin resistance among Mycoplasma genitalium in Denmark, compared to Sweden, where the standard treatment for chlamydia is doxycycline.
Extracts from the Prescription Register suggest that the use of azithromycin for the treatment of chlamydia has decreased but still accounts for about half of the treatments. Its use should be further reduced.
Chlamydia Testing and Positivity Rate by Region and Sex
Across regions and counties, a slight increase in testing frequency was observed from 2022 to 2023 for both sexes, with some exceptions, such as women in Copenhagen City and West Jutland. At the same time, a general decrease in positivity rate was seen across the country, except for men in Bornholm. The highest testing frequency was seen, as in 2022, in Copenhagen City, which also had the lowest positivity rate. The lowest testing frequency was seen in Bornholm. West Jutland had the highest positivity rate for both men and women in 2023, at 19.3% and 10.9%, respectively, which was also the case in 2022.
Testing of Men for Rectal Chlamydia
From 2022 to 2023, a slight increase in the number of confirmed cases of rectal chlamydia among men was observed, Table 7. The increase was evenly distributed across the country, accompanied by an increase in the number of tests. The positivity rate of rectal chlamydia among men remained practically unchanged from 2022 to 2023 (7.8% to 7.6%), suggesting that the slight increase in the number of cases can be explained by the increased testing frequency. The positivity rate of rectal chlamydia increased the most in the Copenhagen Suburbs, North Zealand, Bornholm, and East Zealand, and decreased the most in the Southern Denmark region, where Funen saw an almost halving in the number of cases in 2023 compared to 2022. Central and North Jutland both saw practically unchanged positivity rates and testing patterns from 2022 to 2023.
Lymphogranuloma Venereum (LGV)
At SSI, specific LGV testing using nucleic acid amplification technique (NAT) was performed on 1,825 samples in 2023, of which 1,464 were from men and 359 from women, Table 8. These 1,825 samples came from a total of 1,561 individuals, 1,208 men, 351 women, and two individuals with unspecified gender. This was a decrease in the number of tests for LGV from 2022, where 1,675 individuals were tested, distributed over 1,936 tests. The decrease in the number of tests was mainly seen among women, where LGV is rarely seen, whereas the number of tests for anorectal LGV among men increased from 2022 to 2023 (1,196 vs. 1,333). The number of tests for anorectal LGV among women decreased from 438 to 311, and the number of women tested for LGV decreased from 511 to 351 from 2022 to 2023. Of the 1,313 cases of rectal chlamydia among men, Table 7, 1,208 (92%) were tested for LGV; a similar ratio was seen in 2022 (94%). A slight increase in the number of individuals with confirmed LGV cases was observed from 2022 (77) to 2023 (93). All cases were detected in men in 92 anorectal samples as well as swabs from the throat, urogenital locations, and other sampling sites. No women were diagnosed with LGV in 2023, Table 8.
This annual report is also described in EPI-NEWS no. 35/2024.