Asian people are twice as likely to have a stroke if they have Covid-19, a study has suggested.
Researchers found people from Asian backgrounds made up twice as many stroke patients among a group infected with coronavirus than in a group without it.
While only seven per cent of stroke victims in the non-Covid group of patients were of Asian ethnicity, this surged to 19 per cent among people who had tested positive for coronavirus. This was a bigger increase than in any other ethnic group.
Although the scientists admitted this may partly be because Asian people were more likely to catch the virus in the first place, they said it was ‘unlikely that this is the sole explanation’.
They compared the result to that of Afro-Caribbean black people, who face the highest risk of catching Covid-19 in England but did not suffer the same increase in strokes.
The experts said interpreting the findings is ‘difficult’
Experts suggest the coronavirus thickens the blood, making it easier to clot and triggering a stroke. The body’s inflammatory response may also play a role.
Strokes from Covid-19 are around twice as deadly as usual strokes, this study and others before have shown.
Covid-19 stroke patients were more likely to be Asian than general stroke patients (18.8 per cent vs 6.7 per cent). They were less likely to be white (69.6 per cent vs 83.6 per cent). Black people were slightly more at risk if they had Covid-19 (10.1 per cent vs eight per cent). This was not a ‘significant’ difference, the researchers said
Lead author of the study Dr Richard Perry, of the National Hospital for Neurology and Neurosurgery in Queen Square, London, said: ‘Our study suggests that Covid-19 has had more impact on strokes in the Asian community than in other ethnic groups.
‘We cannot say from our data whether this is because Asians are more likely to catch Covid-19, but it seems unlikely that this is the sole explanation.
‘Evidence from Public Health England suggests, in the UK, people of Afro-Caribbean origin are at the highest risk of catching Covid-19, whereas those of Asian descent have only a marginally higher risk than white people.
HOW DOES THE VIRUS LEAD TO DEADLY BLOOD CLOTS?
The coronavirus appears to cause blood clotting which can lead to deadly strokes, heart attacks or pulmonary embolisms.
While experts are unsure why the virus causes the blockages, there are three main theories:
Some say it could be the result of a an immune overreaction called a ‘cytokine storm’.
Cytokines are chemical-signaling molecules which guide a healthy immune response.
They tell immune cells to attack viral molecules in the body.
But in some people, this response goes into overdrive and immune cells start attacking healthy tissue as well, known as a cytokine storm.
As blood vessels become damaged they can leak, causing blood pressure to drop and driving up the chance of clots forming.
BYPRODUCT OF INFECTION
Other scientists say the surge in strokes may be a byproduct of the way COVID-19 invades the human body.
Professor Ian Jones, a virologist at the University of Reading, told MailOnline: ‘Covid binds to an enzyme called ACE2 which is on the surface of the cell.
‘It simply uses it as a way of attaching itself but in doing so the enzyme function of ACE2 is reduced.
‘The consequence of this is an imbalance of hormones called Angiotensin I and Angiotensin II which together regulate blood pressure.
‘It could be related to the increase in strokes reported.’
VIRUS’ UNIQUE SHAPE
Dr Robert Bonow, a professor of cardiology at Northwestern University, said it may be the coronavirus’ unique shape that is causing the bloodclotting issues.
He said the virus’ spikes, which latch onto receptors in cells, can also attach to blood vessels.
Once they dock onto these blood vessel cells, the viral particles can trigger damage to these as well as to heart muscle, Dr Bonow says.
‘We suspect, therefore, that Asian people who contract Covid-19 may have a higher risk of Covid-19-associated stroke than is seen in other ethnic groups.’
A Public Health England (PHE) report, which covered the period from March to May in line with this study, found only a slight increase of Covid-19 diagnosis in Asian people compared to white.
But since the pandemic has progressed, more research has found the opposite.
A government-run surveillance scheme, by the Office for National Statistics, found that Asian people are up to five times more likely to catch the coronavirus than white people.
The publication in August came after a paper published by PHE in June found that black, Asian and ethnic minority (BAME) Brits had a noticeably higher risk of dying if they caught Covid-19, with Britons of Bangladeshi ethnicity having around twice the risk of white people.
Dr Perry said the findings are likely different because the later studies included ‘silent’ carriers of the coronavirus, and not just those with symptomatic Covid-19.
But he told MailOnline: ‘I do think that [the greater risk of Covid-19 stroke in Asian people] is in part due to a greater risk of catching the infection among Asian people (compared to White people). It is almost bound to be, given that this is what other data has shown.
‘But I suspect that there may be an additional factor. Interpretation of ethnicity data is difficult.’
Previously experts have outlined several reasons as to why ethnic minorities are more likely to become severely ill or die from the virus, admitting it is likely a combination of many.
They may be more likely to catch it initially because they often work in key worker jobs, where they are exposed to the virus more often, and are more likely to be affected by poverty and live in crowded housing.
It is theorised people of BAME background are disproportionately dying of Covid-19 because chronic diseases like type 2 diabetes are more common -which increase the likelihood of severe Covid-19.
Scientists are still investigating whether genetics play any role.
Dr Perry’s colleagues at the stroke hospital, part of the University College London Hospitals NHS Foundation Trust, collected data for stroke patients admitted to 13 hospitals between March and July this year, during the first wave of the coronavirus pandemic.
During this period, there were 86 strokes among patients with a positive Covid-19 test.
These were compared with 1,384 strokes among patients who were admitted during the same time period but had not tested positive for coronavirus.
There are more than 100,000 strokes across the UK each year, and it is the fourth largest cause of death.
The comparison found that Asian people made up a greater proportion of the Covid-19 stroke patients than they did in the general stroke group.
At the same time, the proportions of other ethnic groups represented in the Covid group shrank.
White people made up 70 per cent of the coronavirus group, compared to 84 per cent of the uninfected group.
Black people were slightly more at risk if they had Covid-19 (10.1 per cent vs eight per cent) but this was not a ‘significant’ difference, the researchers said.
All the participants were taken from the same area so ethnic variation would not have been expected to be markedly different across the groups.
The study did not differentiate between people from different parts of Asia – for example East Asia around China, South Asia surrounding India, or the Middle East.
Dr David Strain, a lecturer at the University of Exeter’s medical school, was not involved with the study but said: ‘It is well established that people of South Asian heritage develop stroke approximately 10 years earlier than their counterparts of European descent.
‘This is often described as being a result of premature vascular ageing and a predisposition towards type 2 diabetes.
‘Separately people of South Asian descent have been demonstrated to have a higher risk of hospitalisation, admission and ultimately death due to Covid-19.
‘Further, the two of the biggest risk factors for stroke (namely ischaemic heart disease and type 2 diabetes) are more common in people of South Asian descent and are independent risk factors for Covid-19.
‘Multiple arterial blood clots is a well-recognised complication of Covid-19 and, personally, I have seen multiple ischaemic strokes in people with Covid-19.’
He said he would have wanted to see more detailed information about where the people in the study had been living, in order to rule out bias based on the local population.
The study also found that Covid-19 strokes were more deadly and severe than typical strokes, supporting other studies.
Around 20 per cent of Covid-19 ischaemic stroke patients died, compared with 10 per cent in the control group.
And if they survived, they had more severe disability on discharge.
Stroke can cause long-lasting problems in many areas, including in communication, with difficulties in speaking and writing, and in movement, sometimes leading to paralysis or balance problems.
Levels of D-dimers, a protein marker for the stickiness of blood, were also higher in Covid-19-related strokes than in other strokes.
There was no evidence that Covid-19 stroke patients were younger than usual, or more likely to be men, as has previously been found.
Strokes typically occurred just six days after the main symptoms of Covid-19, which are a persistent cough, high temperature or loss of smell and taste.
Among three patients who had a brain bleed, Covid-19 symptoms occurred an average of four days after the stroke. Although the numbers are small, this difference is significant, say the researchers.
The researchers concluded: ‘Our study provides the most compelling evidence yet that Covid-19-associated ischaemic strokes are more severe and more likely to result in severe disability or death, although the outlook is not quite as bleak as previous studies have suggested.’
The study, published in the Journal of Neurology Neurosurgery & Psychiatry, follows that of the Stroke Research Group at the University of Cambridge.
Academics found at least one in every 100 Covid-19 patients admitted to hospital will suffer a stroke after analysing 61 studies, covering more than 100,000 patients admitted to hospital with the coronavirus.
The team also concluded Covid-19 strokes were deadlier, and that underlying ill health, such as that caused by high blood pressure and diabetes, was a risk factor for coronavirus-linked strokes.
The researchers gave several possible mechanisms for why the coronavirus, once thought to be a purely respiratory disease, causes strokes.
One mechanism might be that the virus triggers an inflammatory response that causes the thickening of the blood, increasing the risk of thrombosis and stroke.
Another relates to ACE2 – a protein ‘receptor’ on the surface of cells that SARS-CoV-2 uses to break into the cell.
This receptor is commonly found on cells in the lungs, heart, kidneys, and in the lining of blood vessels. If the virus invades the lining of blood vessels, it could cause inflammation, constricting the blood vessels and restricting blood flow.
A third possible mechanism is the immune system over-reacting to the infection, with the body then releasing an excessive amount of proteins known as cytokine.
This so-called ‘cytokine storm’ could then cause brain damage, and has also been speculated to damage blood vessels, and cause blood platelets to become more ‘hyperactive’.
An important question is whether the coronavirus is directly increasing the risk of stroke, or whether patients who suffer them were already more at risk, and Covid-19 indirectly led to the event.
Dr Perry and colleagues discussed similar mechanisms behind Covid-19 stroke.
They wrote: ‘We suggest that Covid-19 may provoke the onset of an ischaemic stroke through a variety of thrombotic [clot forming] and inflammatory mechanisms, promoting generation of thrombus [blood clot] in the heart or large vessels or via small vessel occlusion [blockage].
‘Which of these mechanisms manifests in a given patient may be determined by that individual’s conventional vascular risk factors, such as atrial fibrillation [abnormal heart beat], large vessel atheroma [artery narrowing], hypertension [high blood pressure] or type 2 diabetes mellitus.’