Objectives COVID-19 policies have been employed in Denmark since March 2020. We examined whether COVID-19 restrictions had an impact on Chlamydia trachomatis infections compared with 2018 and 2019.

Methods This retrospective nation-wide Danish observational study was performed using monthly incidences of laboratory confirmed chlamydia cases and number of tests, obtained from nation-wide surveillance data. Additionally, Oxford COVID-19 Government Response Tracker data, and Google COVID-19 Community Mobility Reports were used to contextualise the behavioural adaptions seen as a result of COVID-19 policies. Testing rates were compared using Poisson regression and test positivity rates were compared using logistic regression.

Results The crude incidence rate (IR) of laboratory confirmed chlamydia infections was reduced to 66.5 per 105 during the first (March-April 2020) lockdown period as compared to 88.3 per 105 in March-April 2018-2019, but the testing rate was also reduced (Rate ratio 0.72 95% CI 0.71 – 0.73), whereas the odds ratio for a positive test between the two periods was 0.98 (95% CI 0.96 – 1.00). The period of eased COVID 19 restrictions (May – December 2020) and the second lockdown period (December 2020 – March 2021) were characterised by marginally increased crude IRs, while the number of tests performed, and test positivity rates returned very close to the levels seen in 2018-2019. These results were independent of sex, age group, and geographical location.

Conclusion The first Danish COVID-19 lockdown resulted in a reduction in the number of chlamydia tests performed and a consequent reduction in the number of laboratory-identified cases. This period was followed by a return of testing and test positivity close to the level seen in 2018 – 2019. Altogether the Danish COVID-19 restrictions have had negligible effects on laboratory confirmed C. trachomatis transmission.