Strict nonselective quarantine and the prediction of suicidal thinking, hopelessness, and substance use in undergraduates: A longitudinal natural experiment 1000 km from a COVID-19 outbreak

The costs of quarantine on mental health are difficult to quantify and disentangle from primary and secondary effects of infectious disease. Selective and nonselective quarantines were widely used public health measures during the COVID-19 pandemic. Opportunity arose to test by longitudinal natural experiment the hypothesis that nonselective quarantine predicts elevated suicidal thinking, hopelessness, and drug use in a sample that was almost certainly not concurrently exposed to the COVID-19 virus. Undergraduates (18- to 22-years) studying psychology in Dunedin, New Zealand, completed a prospective online survey (10 assessment waves, at 3-day intervals) of passive and active suicidal ideation (past 3 days), current hopelessness, and same-day recreational drug use. During the study, detection of one case of COVID-19 in a community that was 1060 km from the study site triggered a strict nationwide 14-day quarantine, implemented with fewer than 6-hours’ notice. Bayesian growth modelling was used to quantify direct and mediated (indirect) effects of the quarantine period. Of 283 completing baseline assessment, 38.5% (95% CI, 32.8, 44.2) reported past-month ideation and 35.0% (95% CI, 29.4, 40.5) past-fortnight drug use. Retention during follow-up was 89% (n = 253) to 95% (n = 269). At each follow-up, 12.3% to 19.9% reported interval ideation and 1.9% to 4.7% reported drug use. Quarantine predicted a 0.13 standard deviation increase in hopelessness. Quarantine did not directly predict ideation or drug use. However, quarantine had an indirect effect on ideation that was mediated by hopelessness. Among those with average hopelessness, predicted rates of ideation in and out of quarantine were 17.9% and 16.7%, respectively. A nationwide nonselective quarantine predicted increased hopelessness and, in turn, hopelessness predicted small increases in suicidal thinking among emerging adults. The observed effects are unlikely to be attributable to active COVID-19 infection. Public health interventions that ignore developmental, resource, and mental health differences within populations may harm those who are most vulnerable within communities.