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People wait in line to be tested for COVID-19 outside the Elmhurst Hospital Center, in New York, on March 30, 2020.

JEENAH MOON/Reuters

A study of more than 236,000 people in the United States who contracted COVID-19 last year has found that one in three developed a neurological or psychiatric condition and one in 50 of those who became seriously ill received their first diagnosis of dementia within six months.

The most common conditions were anxiety and mood disorders, which occurred in 17 per cent and 14 per cent respectively of those studied. Among patients admitted to intensive care, the researchers found that 7 per cent suffered a stroke and almost 2 per cent developed dementia – which could have been present before COVID-19 but went undiagnosed. They added that more study is needed to fully establish the link between COVID-19 and dementia.

“I think we can have more confidence that there is an increased risk of stroke and an increasing risk of at least uncovering dementia with COVID, and that that really goes along with the severity of the illness,” said Masud Husain, a professor of neurology and cognitive neuroscience at the University of Oxford who co-authored the study.

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The research, published Tuesday in The Lancet Psychiatry, also compared people who had contracted COVID-19 to those who had the flu or another respiratory illness, such as pneumonia or acute bronchitis. The researchers found a 44-per-cent greater risk of neurological and mental health diagnoses after infection with COVID-19 than with the flu and a 16-per-cent greater risk than with other respiratory diseases.

The study is the largest of its kind, and the researchers said the results could have a profound affect on the demand for mental health services and other medical care once the pandemic eases. “What we hope is our data can provide some of the best findings upon which people can begin to model the implications for public health and the health services generally,” said Paul Harrison, a professor of psychiatry at Oxford who was also among the co-authors.

The researchers used a data set from the TriNetX analytics network, which includes 62 health-care organizations, primarily in the U.S., comprising 81 million patients. They tracked 236,379 COVID-19 patients during 2020 and compared them with 236,000 people who had the flu or other respiratory illnesses during the same period.

Overall, the researchers found that 34 per cent of patients with COVID-19 were diagnosed with a neurological or mental health disorder within six months of infection.

The study also found that figure increased along with the severity of the infection – to 39 per cent among those who had been hospitalized and 46 per cent among those admitted to intensive care. One in 50 of all COVID-19 patients suffered a stroke, but that rose to one in 25 among those who were hospitalized and one in 14 among those in ICUs. And while one in 50 people in intensive care developed dementia, that jumped to one in 20 among those who became extremely sick and developed encephalopathy.

“Our view is that a lot of the mental health consequences of COVID are to do with the stress of knowing that one has COVID, and all the implications that go with that, rather than being a direct effect of the virus on the brain or of the immune response to the virus on the brain,” said Dr. Harrison. With regard to the neurological conditions, such as stroke and dementia, he said “there’s more of a reason to think that’s likely to be at least partly mediated by some direct consequence of the COVID infection.”

Dr. Husain said the number of dementia cases was sizable and that the pandemic may be accelerating detection of the condition. “We’re probably uncovering people who might have got it anyway in the next few years,” he said. “It could be that over the next year we’re going to see a lot more patients being referred with dementia, but that group of people might nevertheless have come to us anyway in two years’ time.”

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He said several studies have shown that the virus that causes COVID-19 can enter the brain but does not appear to attack neurons. “But it can cause inflammation and it can activate inflammatory cells in the brain and the cells in the blood vessels in the brain,” which can lead to clotting.

“This is a very important topic, as there has been considerable consternation regarding COVID-19 as a ‘brain disease,’” said Musa Sami, an associate professor of psychiatry at the University of Nottingham. “This data provides very important information for services and policy-makers to estimate the burden of neurological and psychiatric disease from COVID-19.”

Health columnist André Picard answers reader questions about COVID-19 variants, how effective the various vaccines are and the impact of on-again, off-again lockdowns. The Globe and Mail

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