Background: Attention should be paid to delirium in coronavirus disease 2019 (COVID-19) patients, especially older people, since advanced age poses increased risk of both delirium and COVID-19-related death.

Objective: This study aims to summarise the evidence on prevalence, incidence and mortality of delirium in COVID-19 patients.

Methods: We conducted a comprehensive literature search on Pubmed and Embase from inception to 1 December 2020. Three independent reviewers evaluated study eligibility and data extraction, and assessed study quality. Outcomes were analysed as proportions with 95% confidence interval (CI). We also compared mortality differences in COVID-19 patients using odds ratio.

Results: In total, we identified 48 studies with 11,553 COVID-19 patients from 13 countries. Pooled prevalence, incidence and mortality rates for delirium in COVID-19 patients were 24.3% (95% CI: 19.4-29.6%), 32.4% (95% CI: 20.8-45.2%) and 44.5% (95% CI: 36.1-53.0%), respectively. For patients aged over 65 years, prevalence, incidence and mortality rates for delirium in COVID-19 patients were 28.2% (95% CI: 23.5-33.1%), 25.2% (95% CI: 16.0-35.6%) and 48.4% (95% CI: 40.6-56.1%), respectively. For patients under 65 years, prevalence, incidence and mortality rates for delirium in COVID-19 patients were 15.7% (95% CI: 9.2-23.6%), 71.4% (95% CI: 58.5-82.7%) and 21.2% (95% CI: 15.4-27.6%), respectively. Overall, COVID-19 patients with delirium suffered higher risk of mortality, compared with those without delirium (OR: 3.2, 95% CI: 2.1-4.8).

Conclusion: Delirium developed in almost 1 out of 3 COVID-19 patients, and was associated with 3-fold overall mortality. Our findings suggest that first-line healthcare providers should systematically assess delirium and monitor related symptoms among COVID-19 patients.