People who test positive for COVID-19 are at an increased risk of Alzheimer’s disease, Parkinson’s disease and ischemic stroke, a large new study finds.

Investigators analyzed the health records of over half the Danish population and compared neurological outcomes in patients with COVID-19 diagnoses to those of influenza patients from the pre-pandemic period.

Of the more than 919,000 individuals who were tested for COVID-19 within the study period, about 43,300 tested positive. These individuals were 3.5 times more likely to be diagnosed with Alzheimer’s disease and 2.6 times more likely to be diagnosed with Parkinson’s disease than their peers who did not have COVID-19, reported Pardis Zarifkar, MD, of the Department of Neurology, Rigshospitalet, in Denmark. 

They also had 2.7 times greater odds of experiencing an ischemic stroke and 4.8 times the likelihood of increased bleeding in the brain.

But these adverse associations do not appear to stray too far from those of other viral infections studied, they noted. 

“Reassuringly, apart from ischemic stroke, most neurological disorders do not appear to be more frequent after COVID-19 than after influenza or community-acquired bacterial pneumonia,” Zarifkar said in a statement.

In addition, the frequency of other neurodegenerative illnesses did not increase with COVID-19, flu or pneumonia, Zarifkar and colleagues added. These included multiple sclerosis, myasthenia gravis, Guillain-Barré syndrome and narcolepsy.

“These findings will help to inform our understanding of the long-term effect of COVID-19 on the body and the role that infections play in neurodegenerative diseases and stroke,” the authors concluded.

Full findings were published in the journal Frontiers in Neurology.

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