Chlamydia - disease prevalence report 2022
Data from the Danish Microbiology Database
As in the previous years, the data needed for the preparation of the present report covering 2022 were collected via the Danish Microbiology Database (MiBa). The data comprise all positive and negative test results for oculo-genital infection caused by Chlamydia (C.) trachomatis at all departments of clinical microbiology (DCMs). The data include civil registration numbers, and disease episodes can therefore be delimited to the individual level. A new disease episode is defined as an interval of more than 42 days between two positive test episodes. Several negative test results within a single year are counted as a single negative testing episode. For patients with a valid civil registration number, information about the municipal code and thereby the area and region is collected from the Danish civil registration system.
In the current report for 2022, numbers from 2021 are often provided to allow for comparison. Until and through 2015, monitoring was based on direct notifications from the DCMs, as presented in Table 1. The differences between the two methods are described in EPI-NEWS 34/2016. Through 2021, the numbers presented in Table 1 were shown for the number of persons tested. In the present report, the number of testing episodes from 2011 to 2022 has been added.
The extent of chlamydia testing performed in private laboratories remains unknown. Such data are not included in this report. When rectal chlamydia is established or on suspicion of lymphogranuloma venereum (LGV), EPI-NEWS 20/2008, some DCMs and clinics that perform testing for sexually transmitted diseases (STI clinics) submit material to Statens Serum Institut (SSI) for relevant specialized LGV testing.
In 2022, a total of 287,148 persons (199,396 women, 85,808 men and 1,943 of unknown sex) were tested for chlamydia by a total of 307,111 testing episodes, whereas the number of detected cases was 41,634. This constituted an increase from 2021, when the number of detected cases was 36,642 among 272,809 tested persons in 289,792 testing episodes.
Since 2011, an increase has been observed in the number of testing episodes, apart from 2020 and 2021, due to the COVID-19 restrictions, EPI-NEWS 47/2022. The number of chlamydia cases increased considerably in 2022, which may possibly be explained by the lifting of the restrictions and possibly by increased travel activity following the COVID-19 pandemic, Table 1. Only some records of tested persons include information of sex, age and area. Therefore, positive rates may vary in the following.
Table 2 divides the numbers by sex and age groups and presents the number of chlamydia cases and the incidence rate per 105 inhabitants. From 2021 to 2022, the case incidence rate increased for all age groups >15 years, except for women aged 45-49 years. A decline was observed for all age groups <15 years for both sexes. The group of 15-29-year-olds comprised the largest share of the cases and has remained stable at around 81% for men and 89% for women since 2017. In 2022, men comprised 42% of the diagnosed cases, which was in line with the share recorded in 2021.
Overall, the male to female incidence ratio (MFIR) was 0.72. MFIR was <1 among 10-29-year-olds and >1 in the 1-year and the 30+year age groups. The highest MFIR (2.51) was recorded in the 50+year age group.
Among the 15-29-year-olds, the incidence rate of detected chlamydia cases increased from 2021 to 2022 for both sexes. The highest incidence rate among women was observed among 19-year-olds (7,882 cases per 105). Among men, the highest incidence rate was seen among 20-year-olds (4,283 cases per 105). Generally, the distribution of cases in this age group was highly comparable to those recorded in previous years. As in the preceding years, women had a higher incidence rate than men in the 15-29-year age group.
From 2021 to 2022, the national incidence of laboratory-detected chlamydia cases (per 105 inhabitants) increased for men and women alike. Among men, the incidence rate increased in all areas, except for Bornholm, where a slight decline was observed. The greatest increases were seen in Copenhagen subs., North Zealand and East Zealand. Among women, corresponding incidence rates were recorded in all areas. The largest increase was recorded in East Zealand. The overall national MFIR was 0.72 (2021: 0.73). The most notable change was an MFIR decline on Bornholm from 0.64 in 2021 to 0.51 in 2022.
Among patients who had chlamydia detected, 91% were tested by general practitioners or medical specialists and 9% by hospital departments, as in 2021. All cases were detected using nucleic acid amplification techniques (NAT). In 2022, chlamydia was detected in urine samples in 16,478 cases (2021: 14,760), i.e. 40% of all cases, which is in line with the numbers recorded in 2021. Male samples constituted 88% of the positive urine samples. Urine was the sampling material used in 87% of men with chlamydia. This figure has remained practically unchanged for the past five years.
Chlamydia in children
Chlamydia was diagnosed in 121 children under 15 years of age (182 in 2021), including 69 aged 1-14 years (120 in 2021). In the 10-14-year age group, seven chlamydia cases were seen in boys and 62 in girls (14 and 102 cases, respectively, in 2021). The incidence per 105 among 10-14-year-olds was 4 for boys (8 in 2021) and 38 for girls (63 in 2021). The figures for 2021 and 2022 are presented in Table 2.
Among the 62 girls who had chlamydia detected, 54 girls were 14 years old. Among these, 44 had findings of chlamydia by urogenital swabbing or urine; for three cases, no swab location was stated; one case was detected by eye swab; one case by rectal swab; and five cases were detected by throat swab. Additionally, five 13-year-old girls tested positive by urogenital swabs and one by a throat swab. Two 12-year-old girls had chlamydia detected by throat and urogenital swabs, respectively. Among boys, six 14-year-olds and one 13-year-old boy had chlamydia detected in the urine/urethra.
In 2022, chlamydia was detected in ocular samples from 52 children < 1 year, among whom 39 were less than one month old (in 2021, this figure was 47 of 55 children). One child tested positive by tracheal swabbing, whereas the rest tested positive by ocular swabbing.
Age groups and sex for chlamydia cases and in the tested population
Generally, an increase was recorded in the incidence rate of tested men and women from 2021 to 2022, except for the age group <1 year, Table 4. However, the incidence rate of tested men (3,139 per 105) was considerably lower than the rate of tested women (7,132 per 105). This applied in all age groups, except for boys < 1 year and men 50+ years. From 2021 to 2022, the positive rate increased among tested women, from 11% to 11%, but declined for men, from 20% to 19%. The most notable change was the decline in positive rate in the 10-14-year age group, which decreased by 5.1 percentage points for men and 5.7 percentage points for women. For 10-14-year-old boys and 15-29-year-old men, the positive rate declined, which may indicate that men in this age group have become more aware of testing. The highest positive rate was observed for 15-19-year-old men (34%) and for 15-19-year-old women (26%).
In 2019 (No. 38 - 2019 (ssi.dk)), it was recommended to use doxycykline rather than azithromycin for treatment of uncomplicated chlamydia The reason was the high occurrence of azithromycin resistance among Mycoplasma genitalium in Denmark compared with Sweden where the standard treatment was doxycycline.
Data extraction from the Prescriptions Register indicates that the use of azithromycin for treatment of chlamydia has declined, but also that it still accounts for approx. half of the treatments. This consumption should be reduced further.
Area and sex for chlamydia cases and in the tested population
Overall and in most areas, the number of men and women (per 105 inhabitants) tested in 2022 increased compared with 2021, Table 5. Across Denmark, the share of tested women was more than twice as high as the share of tested men (women: 7,115 per 105 inhabitants, men: 3,122 per 105 inhabitants). At the national level, the positive rate increased for women and declined for men from 2021 to 2022. For women in the City of Copenhagen, East Zealand and Bornholm, the positive rate increased, whereas it remained largely unchanged in the rest of Denmark compared with 2021.
For men, an increase was observed in the positive rate in North and East Zealand, while a large increase in the positive rate was seen in South, East and North Denmark.
Testing of men for rectal chlamydia
The incidence rate of men who underwent rectal chlamydia testing increased from 265 in 2021 to 332 in 2022, Table 6. The incidence rate for testing followed an increasing trend across Denmark, particularly in North Jutland, where the rate nearly doubled compared with 2021. Despite the increased testing incidence rate, the positive rate increased from 12% in 2021 to 13% in 2022. The total share of detected rectal chlamydia cases in men increased by 32%; from 935 in 2021 to 1,237 in 2022. The positive rate increased in the following areas: Copenhagen City, East Zealand, West and South Zealand, Funen, South Jutland, West Jutland and East Jutland. In contrast, the positive rate declined from 2021 to 2022 in Copenhagen Subs, North Zealand, on Bornholm and in North Jutland. Nationally, a 27% increase was recorded in the number of rectal chlamydia tests (2021: 7,714, 2022: 9,779), which may possibly be explained by an increasing number of tests being performed in men receiving pre-exposure prophylaxis (PrEP) against HIV.
Due to errors in Table 6 published in previous years on rectal chlamydia testing of men, the figures describing 2021 are not in line with the 2021 figures published in previous annual reports.
In a separate section of EPI-NEWS no. 38/2023, we present the revised male rectal chlamydia tables for the 2011-2022 period.
The SSI performed specific LGV testing using NAT on 1,671 samples, among which 1,160 were from men and 511 were from women. A total of 1,932 tests were made, compared with 1,236 in 2021.
The number of ano-rectal samples was 1,632, including 1,194 from men and 438 from women. LGV testing was performed in 91% of men with anorectal chlamydia, which is unchanged from 2021, when the corresponding percentage was 92%. A steep increase was observed in the number of detected LGV cases from 2021 (16) to 2022 (76). All cases that were detected in men were found in a total of 77 anorectal samples, one throat swab, and eight samples for which no swab location was provided. One woman had LGV detected by an anorectal swab. This is the first LGV case recorded in a woman since 2018 in Denmark.