Cognitive sequelae in post-COVID-syndrome: a Danish-Swedish case-control study.

Background: While patients with post-COVID syndrome (PCS) suffer from cognitive deficits few studies directly compare patients with PCS to subjects recovered after an infection with the 'Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)'.

Objectives: To investigate cognitive performance adjusting for age, increasing body-mass-index (BMI), smoking, years of education, gender and hospitalisation while infected in patients with PCS compared to controls fully recovered. Secondly, to stratify cognitive performance based on the SARS-CoV-2 virus strain (variant of concern 'VOC') causing the infection. Thirdly, to assess whether patients with PCS have increased levels of psychological distress and affected hand grip strength as both are associated with cognitive performance.

Methods: A Danish-Swedish case-control study we recruited adult patients (18-75 years) with PCS from long-COVID outpatient clinics in Region Zealand Denmark and Skåne County Sweden. Participants had confirmed SARS-CoV-2 infection >12 weeks prior to inclusion and healthy control subjects had recovered completely. All study participants were exposed to cognitive tests, Kessler's psychological distress scale (K10) and tested with a hand-dynamometer.

Results: Recruiting 181 cases and 155 control subjects, patients with PCS had reduced cognitive performance scores on all domains though hardly clinically significant. Reduced processing speed was impacted the most with patients infected early in the pandemic exhibiting greater deficits.

Conclusion: PCS was associated with reduced cognitive processing speed compared to fully recovered controls with those infected early in the pandemic having greater deficits. Psychological distress and hand grip strength were affected in patients with PCS, but not decisively associated with cognitive performance.