Chlamydia 2017

Chlamydia 2017

Up to and including 2015, the laboratory notification system for chlamydia (oculogenital infection caused by Chlamydia trachomatis) was based on the statutory quarterly submission of data on laboratory-confirmed chlamydia made by the clinical microbiology departments and in recent years also by one clinical bio-chemistry department. For 2015, data were also obtained via The Danish Microbiology Database (the MiBa) (

The differences between the two methods is described in EPI-NEWS 34/16. Data for 2016 onward are retrieved exclusively from the MiBa. Since 1 January 2015, the chlamydia reports provided at Numbers and Graphs (Danish language: Tal og Grafer) have been MiBa-based.

Data from the MiBa

The data comprise all positive and negative results from chlamydia tests from one department of clinical biochemistry and from all departments of clinical microbiology (DCMs) extracted from the MiBa. The data include the patients’ civil registration number, and disease episodes can therefore be delimited to the individual level. A new disease episode is considered to be diagnosed if there is 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 annual report for 2017, numbers from 2016 are often provided to allow for comparison. Due to continuous updates made to data in the MiBa, each of these numbers differs marginally from the corresponding numbers published in EPI-NEWS 34/17.

Other data

The extent of chlamydia testing performed in private laboratories that market themselves via the internet remains unknown. Such data are not included in this annual report.
When rectal chlamydia is established or when lymphogranuloma venereum (LGV) is suspected, some DCMs and STI clinics submit material to the SSI for relevant specialised testing.

Chlamydia incidence

In 2017, a total of 267,862 persons were tested for chlamydia (263,969 in 2016), and the number of detected cases was 32,931 (34,132 in 2016), Table 1. The annual incidence was 570 per 105 (594 per 105 in 2016 and 558 per 105 in 2015). In the 2004-2015 period, chlamydia monitoring was based on quarterly reports from the laboratories; and the positive rate was calculated with the number of analysis made as the denominator. For data extracted from the MiBa as from 2010, the number of persons tested is used as the denominator. Therefore, the previously reported 9% positive rate from 2015 (previous method) is not directly comparable with the MiBa-based positive rates of 12.3% in 2017, 12.9% in 2016 and 12.3% in 2015.

Sex and municipality were stated for 32,737 patients, and sex and age were stated for 32,931 patients. This explains the minor differences between the positive rates in some of the following tables.

Distribution of cases and incidence by sex and age group are presented in Table 2. Men accounted for 40% of the diagnosed cases. This proportion has increased steadily from 23% in 1994 to 38% in 2009-2012. For both sexes, the majority of cases were observed among 15-29-year-olds: 80% among men and 88% among women. The incidence was also significantly higher in this age group than in the group aged 30 years of age and above. Compared with 2016, the incidence declined for both sexes in all five-year age groups in the 15-39 years interval. For men, a slight increase was seen in the incidence among 40-44-year-olds, and a rather considerable increase was seen among the 45-49-year-olds.


In 2017, the incidences for both men and women were lower than those recorded in the preceding year for nearly all 1-year age groups in the 15-29-year age range, Figure 1. The highest incidence among men was found in 20-year-olds (21-year-olds in 2016). In women, the highest incidence was found among 19-year-olds, as was also the case in 2016.


Geographical distribution of chlamydia cases

The chlamydia incidence among men as well as women was highest in the City of Copenhagen, followed by East and North Jutland. Both overall and in the majority of areas, the incidence declined for both sexes in 2017 compared with 2016, Table 3. An increase was observed, particularly among women, in East Jutland and for both sexes in South Jutland. The ratio between the incidence for men and women was slightly higher in 2017 than in 2016 for Denmark overall and in the following areas: The City of Copenhagen, West & South Zealand, South Jutland, West Jutland and North Jutland.



Among the positive samples, 90% were submitted by general practitioners and 10% by hospitals (92% and 7%, respectively, in 2016). All cases were detected using nucleic acid amplification techniques. All laboratories reported positive findings in urine samples.

Chlamydia was detected in urine samples in 13,592 cases, i.e. 40% of all cases (40% in 2016). Male samples constituted 87% of the positive urine samples (86% in 2016). Urine was used as sample material in 89% of the male chlamydia cases (87% in 2016 and 84% in 2015).

Chlamydia in children

Chlamydia was found in 153 children below 15 years of age (143 in 2016).

In the 10-14-year age group, nine chlamydia cases were seen in boys and 74 in girls (5 and 82 cases, respectively, in 2016). The incidence per 105 among 10-14-year-olds was 45 for girls (50 in 2016) and 5 for boys (3 in 2016), Table 2.

The tested population

Age groups and sexes
As previously, the incidence of tested persons was considerably lower among men (2,700 per 105) than among women (6,556 per 105), Table 4, except for 0-year-olds and ≥ 50-year-olds. The total number for 2017 was in line with that recorded for 2016, but was lower for men aged 20-29 years and for women aged 15-34 years. The overall positive rate declined for both sexes, and this trend applied to nearly all age groups, except 45-49-year-old men.


Areas and sexes
Both totally and in all areas, the number of men tested per 105 increased from 2016, but the increases recorded were very limited, Table 5.

For Denmark overall, the positive rate was slightly lower for men (17.3%) as well as for women (10.3%) than in 2016 (18.2% and 10.9%, respectively).

For men and women alike, a modest increase was seen in the positive rate in South Jutland, whereas a modest decline was observed in most other areas.


Testing of men for rectal chlamydia
Rectal chlamydia was detected in 734 men (546 in 2016).

The incidence of rectal testing of men, Table 6, continued to increase and in 2017 reached 136 per 100,000 (112 per 100,000 in 2016).

As in 2016, considerable geographic variation was seen with respect to testing activity. The highest level of activity was seen in Copenhagen City, on Funen and in East Jutland, i.e. areas that comprise large cities with universities and STI clinics.

Compared with 2016, the testing activity in the Capital Region of Denmark increased 1.2-1.5 fold; in Region Zealand it doubled; in The Region of Southern Denmark and in the Central Denmark Region, the rate remained virtually unchanged; and in the North Denmark Region, it was nearly halved.

The positive rate also varied: The largest increases were observed in Copenhagen Subs., North Zealand, East Zealand and East Jutland. The largest decline was seen on Funen.


Lymphogranuloma venereum (LGV)
Material was submitted for LGV testing from 723 patients (470 men, 250 women and in three cases the sex was not stated). The number of ano-rectal samples was 529 (348 men, 178 women and in three cases the sex was not stated). LGV was detected in 40 men aged 23-77 years (in 37 ano-rectal samples, one urethral samples and two unspecified samples) and in one 37-year-old woman (a rectal sample).

This report is also described in EPI-NEWS 38/18.