No 38 - 2018

Chlamydia 2017

The report on detected chlamydia infections (oculogenital infection caused by Chlamydia trachomatis) is based on data from the Danish Microbiology Database (the MiBa), and comprises all positive and negative results of chlamydia tests. A new disease episode is defined by an interval exceeding 42 days between two positive test episodes. Several negative test results within a single year are counted as a single negative testing episode.

For a detailed epidemiological description of the 2017 incidence, please see the 2017 annual chlamydia report.

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). The annual incidence was 570 per 10⁵ (594 per 10⁵ in 2016 and 558 per 10⁵ in 2015).

In 2017, the number of persons tested for chlamydia was thus 1.5% higher and the number of detected cases was 3.5% lower than the corresponding figures for 2016, and the positive rate declined from 12.9% in 2016 to 12.3%

At first sight, it seems encouraging that more people are being tested for chlamydia and that the total number of tested cases was lower in 2017 than in 2016. Nevertheless, the mentioned increase in the number of tested persons almost exclusively occurred among persons aged 30 years and above, among whom the positive rate is considerably lower than in the tested population in general, whereas the sampling activity declined in the 15-29 age group, where the occurrence of chlamydia peaks. The declining positive rate may therefore reflect an inexpedient age distribution in the tested population.

For both sexes, the majority of cases were detected in the 15-29 year age group: 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.

More than twice as many women as men were tested for chlamydia, but the men’s share of the detected cases still only comprises 40%, and the share of samples in men who test positive for chlamydia is considerably higher in nearly all age groups than among women. An increased sampling activity in men is therefore needed.

All in all, these numbers suggest that the testing activity may still be optimised with respect to sex and age groups.

There are grounds for further enhanced preventive action, especially among 15-29-year-olds, particularly among men. There is a need for increased attention to information about safe sexual behaviour, increased sampling activity and partner information in case of positive findings.

The number of men who had rectal chlamydia detected increased further compared with 2016, but considerable geographical differences exist with respect to how often rectal samples are taken. When rectal chlamydia is found in men, these men should be tested for HIV, syphilis and gonorrhoea, and the sample material should be tested for the variant of C. trachomatis that may cause lymphogranuloma venereum (LGV).

For treatment of uncomplicated chlamydia, the Danish Health Authority recommends azithromycin 1g administered orally as a single dose, or doxycycline 100 mg x 2 administered orally for seven days. These two drugs are equally effective in the treatment of uncomplicated genital chlamydia, and resistance to both drugs is considered rare. Doxycycline is recommended for the treatment of rectal chlamydia as well as for LGV in which case treatment should be continued for 21 days.

Azithromycin is used much more frequently than doxycycline in the treatment of chlamydia in Denmark. Presumably, this is the reason why Denmark records a much higher occurrence of azithromycin resistance among Mycoplasma genitalium than Sweden does. In Sweden, doxycycline is used in the treatment of chlamydia and uretritis/cervicitis of unknown aetiology. If this unfortunate trend continues in Denmark, infection with M. genitalium may become a condition that is very difficult and costly to treat.

To slow down the development of resistance in M. genitalium, it should be considered to change the standard treatment of chlamydia to doxycycline, as in other European recommendations.

(S. Hoffmann, Department of Bacteria, Parasites & Fungi; K.D. Bjerre, Data Integration and Analysis Secretariat (DIAS), Department of Infectious Disease Epidemiology and Prevention)