With more than 230,000 reported cases across the 27 European Union/European Economic Area (EU/EEA) countries in 2024, chlamydia is the most frequently notified sexually transmitted infection (STI) in the region. Since 2014, notification rates generally had been going up in most of the 20 countries in the EU/EEA with consistent reporting and comprehensive disease surveillance.
A first peak was reached in 2019, followed by a drop during the years of the COVID-19 pandemic. Chlamydia notifications bounced back up again in 2022 and went down again slightly in 2023.
Unexpected drop in chlamydia notifications in 2024
Beginning of 2025, Sweden shared a nation-wide decrease in notified chlamydia cases for 2024, via EpiPulse Events, a European Union event-based surveillance platform hosted by the European Centre for Disease Control and Prevention (ECDC). They also informed that this decline was mainly seen among young people despite unchanged testing policies.
Responding to this information, Denmark, England, Finland, Ireland, Norway and the Netherlands reported similar trends for 2024.
In their Euroroundup published in Eurosurveillance, Astorga Alsina et al. present an analysis of chlamydia notification data and trends between 2015 and 2024 for each of the seven countries that observed a decline in chlamydia cases during 2024. The authors also summarise hypotheses on potential drivers behind these. [1]
The described reductions in chlamydia cases in the seven countries were unexpected in their magnitude and evenly distributed geographically, i.e. the decline in case notifications was noted reporting across almost all subnational regions of the affected countries.
Denmark saw a drop of chlamydia case notifications by 19% between 2023 and 2024 (from 37,111 to 29,946 cases) with 17% and 22% declines in males and females, respectively. Case notifications declined between 12% and 32% across all regions.
In England, the number of recorded chlamydia cases went down by 13% in 2024 compared with 2023 (194,143 to 168,889 cases) – across sexes, age groups and regions. The largest decrease (18%) occurred among people aged 15-24 years. During this period, the total tests decreased by 1%. Since 2020, the possibility to order self-sampling tests online, has been the most common test setting among young people in England, surpassing tests by specialist sexual health services and general practitioners.
Finland had observed a steady increase in chlamydia cases in the years before 2024. Between 2023 and 2024, notifications fell by 17% from 17,551 to 14,486 cases. The decrease was noted in both males and females across age groups, mostly among those aged 20-24 years (-22%), and across 21 of 23 Finnish regions.
In 2024, Ireland observed a 16% decrease (from 13,699 to 11,524 cases) in chlamydia notifications across all health regions compared with 2023. Notably, among those aged 15-24 years, cases declined by 21% in both males and females, with the largest reduction of 28% among males aged 15–19 years. According to preliminary data for 2025, the trend continued into the first 6 months of the year. From 2023 to 2024, testing recommendations for chlamydia remained unchanged in Ireland with a national free home STI testing service introduced in June 2024.
The Netherlands recorded 20,174 chlamydia cases in 2024 compared with 24,048 in 2023, constituting a decline of 16% in one year. This decrease occurred across most age groups, notably among those aged 20-24 years (-21%) and was registered across all regions in the country. Overall testing went down as did test positivity.
With 18% fewer reported chlamydia cases in 2024 (down from 28,137 to 23,100), Norway saw a decrease across all counties, with notifications declining by 14% in males and 20% in females, respectively. The largest reduction was among those aged 20-24 years. Chlamydia testing activity decreased in 2024 in Norway, mostly due to fewer tests performed among people younger than 25 years.
In Sweden, chlamydia cases also dropped by 18% between 2023 and 2024, from 32,298 to 26,392 cases. Mainly younger age groups across both sexes accounted for this regression, with the largest reduction in those aged 20-24 years (-24%). There were no changes in testing practices, laboratory methods, public health interventions or campaigns that could explain the decrease in chlamydia in Sweden.
Testing volumes varied but test positivity overall decreased
In some countries, the decline in chlamydia notifications was accompanied by reduced testing: Denmark, England the Netherlands and Norway reported a decrease in overall testing volumes. England saw the largest reductions among people aged under 25 years particularly in online testing services.
The authors note that while changes in testing volumes varied, all countries observed a decrease in test positivity, suggesting a possible reduction in prevalence within the tested population.
Some of the countries saw decreases in other STI such as gonorrhoea while others saw stable or increased gonorrhoea reporting. Overall, however, the observed chlamydia decreases in all the countries were unexpected in their magnitude and generated several hypotheses.
Amongst other factors, the authors hypothesise about a collateral effect of targeted interventions addressing rises in gonorrhoea notifications which could have had a positive effect on chlamydia as well: "No major surveillance changes were identified and changes in testing policies targeting young people do not fully explain the observed declines. Possible drivers include a combination of sexual health promotion campaigns, changes in the risk profile of those accessing testing and long-term impacts of COVID-19. While variations across national contexts may favour country-specific hypotheses, the similar timing and pattern of the changes suggests a possible common driver."
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