To perform a population-based comparative study assessing the mortality in those with premorbid neurological syndromes and the incidence, types, and outcomes of new neurological sequalae after developing COVID-19 infection.

Defining the mortality, incidence, specific disorders, and outcomes of neurological complication(s) of COVID-19 are imperative for understanding risk status as well as recognition of emerging neurological syndromes that may influence healthcare needs. Moreover, a fuller grasp of this neurological disease burden enables better planning for clinical management.

Using health service data collected from March 1, 2020, to June 30, 2021, we constructed a cohort of SARS-CoV-2 RNA-positive (n=177,892) and -negative (n=177,800) adults who were age-, sex-, and comorbidity-matched, not yet vaccinated, and underwent RT- PCR testing at similar times. COVID-19 associated mortality rates were examined within the cohort. Neurological sequelae were analyzed during the acute (less than three months) and the post-acute (three to nine months) phases post-infection. 

The risk of death was significantly greater in the SARS-CoV-2 RNA-positive (2,140 per 100,000 person years) compared to RNA-negative (922 per 100,000 person years) over a follow-up of 9 months, particularly amongst those with premorbid neurological disorders: adjusted odds ratios (aOR, 95% CI) in persons with a history of parkinsonism (1·65, 1·15-2·37), dementia (1·30, 1·11-1·52), seizures (1·91, 1·26-2·87), encephalopathy (1·82, 1·02-3·23), and stroke (1·74, 1·05-2·86). There was a significantly increased risk of new onset neurological sequelae during the acute time phase after COVID-19 including encephalopathy (2·0, 1·10-3·64), dementia (1·36, 1·07-1·73), seizure (1·77, 1·22-2·56), and brain fog (1·96, 1·20-3·20). These risks persisted into the post-acute time phase after COVID-19 during which inflammatory myopathy (2·57, 1·07-6·15) and coma (1·87, 1·22-2·87) also became significantly increased.

Persons with SARS-CoV-2 infection and premorbid neurological disorders are at greater risk of death while SARS-CoV-2 infection was complicated by increased risk of new onset neurological disorders following COVID-19.