A nationwide study of Chlamydia trachomatis infections in Denmark during the COVID-19 pandemic (preprint)

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.

Preterm birth, stillbirth, and early neonatal mortality during the Danish COVID-19 lockdown (preprint)

Importance Using provisional or opportunistic data, three nationwide studies (The Netherlands, USA, and Denmark) have identified a reduction in preterm or extremely preterm births during periods of COVID-19 restrictions. However, these findings have been challenged as none of the studies accounted for perinatal deaths. Objective To determine whether the reduction in extremely preterm births, observed in Denmark during the COVID-19 lockdown, could be a result of an increase in number of perinatal deaths; and to assess the impact of extended COVID-19 restrictions on the prevalence of preterm birth and perinatal death. Design The study is a nationwide Danish register-based prevalence proportion study using detailed data to capture all births (induced abortions were excluded) throughout Denmark. We assessed the prevalence of stillbirth, preterm birth, and early neonatal death. Setting Population-based study Participants All singleton pregnancies delivered in Denmark, between February 27, and September 30, 2015-2020. COVID-19 lockdown was studied in 31,164 births and the extended period of COVID-19 restrictions in 214,862 births. Exposure COVID-19 restrictions broadly (February 27, – September 30, 2020) or COVID-19 lockdown specifically (March 12, – April 14, 2020). Main Outcome Prevalence of preterm births, stillbirths and early neonatal deaths across the periods under study. Results The extremely preterm birth rate was reduced (OR 0.27, 95% CI 0.07 to 0.86) during the strict lockdown period, while perinatal mortality was not significantly different. During the extended period of restrictions, the extremely preterm birth rate was marginally reduced, and a significant reduction in the stillbirth rate (OR 0.69, 0.50 to 0.95) was observed. No changes in early neonatal mortality rates were found. Conclusion and Relevance Stillbirth and extremely preterm birth rates were reduced in Denmark during the period of COVID-19 restrictions and lockdown, respectively, suggesting that aspects of these containment and control measures confer an element of protection. The present observational study does not allow for causal inference; however, the results support design of studies to ascertain whether behavioural or social changes for pregnant women may improve pregnancy outcomes. Funding None Key points Question Can changes in stillbirth and early neonatal mortality rates during the COVID-19 lockdown explain the reduction in extremely preterm birth seen in Denmark? Findings In this nationwide register-based study that included data pertaining to 245,999 pregnancies, the statistically significant reduction in extremely preterm birth during the COVID-19 lockdown was confirmed. The stillbirth and early neonatal mortality rates were unchanged during lockdown, while the stillbirth rate was reduced over the extended period of COVID-19 restrictions. Meaning The reduction in extremely preterm births seen during the COVID-19 lockdown in Denmark is not a result of increased stillbirth or early neonatal death.