Heterogeneity in depressive and anxiety symptoms and loneliness during the COVID-19 pandemic: Results from three Dutch psychiatric case-control cohorts from April 2020 to February 2022

Objective: While research found heterogeneous changes in mental health during the COVID-19 pandemic, less is known about the long-term changes in mental health in psychiatric groups. Therefore, we applied a data-driven method to detect sub-groups with distinct trajectories across two years into the pandemic in psychiatric groups, and described their differences in socio-demographic and clinical characteristics. Method: We conducted sixteen rounds of questionnaires between April 2020 and February 2022 among partic-ipants (n = 1722) of three psychiatric case-control cohorts that started in the 2000's. We used Growth Mixture Modelling and (multinomial) logistic regression to identify characteristics associated with trajectory membership. Results: We found low decreasing (1228 [72%] participants), intermediate (n = 348 [22%] participants) and high stable (106 [6%] participants) trajectories of depressive symptoms; decreasing low/intermediate (1507 [90%] participants) and high stable (161 [10%] participants) trajectories of anxiety symptoms; and stable low (1109 [61%] participants), stable high (315 [17%] participants), temporary lowered (123 [9%]) and temporary heightened (175 [13%] participants) trajectories of loneliness. Chronicity and severity of pre-pandemic mental disorders predicted unfavourable sub-group membership for all outcomes. Being female, having a low education and income level were associated with unfavourable trajectories of depression, being younger with unfavourable trajectories of anxiety and being female and living alone with unfavourable trajectories of loneliness. Conclusion: We found relatively stable trajectories of depression and anxiety symptoms over two years, sug-gesting low heterogeneity in outcomes during the pandemic. For loneliness, we found two specific sub-groups with temporary increase and decrease in loneliness during the pandemic.