, new research shows.
The study among Medicare beneficiaries with COVID-19 also showed that stroke risk is higher for relatively young older adults, those aged 65 to 74 years, and those without a history of stroke.
The study highlights the impact COVID-19 has on the cardiovascular system, said study author Quanhe Yang, PhD, senior scientist, Division for Heart Disease and Stroke Prevention, Centers for Disease Control and Prevention, Atlanta.
“Clinicians and patients should understand that stroke might be one of the very important clinical consequences of COVID-19.”
The study was presented during the hybrid International Stroke Conference held in New Orleans and online. The meeting was presented by the American Stroke Association, a division of the American Heart Association.
Stroke is the fifth leading cause of death in the U.S. As an increasing number of people become infected with COVID-19, “it’s important to determine if there’s a relationship between COVID and the risk of stroke,” said Dr. Yang.
Findings from prior research examining the link between stroke and COVID-19 have been inconsistent, he noted. Some studies found an association while others did not, and in still others, the association was not as strong as expected.
Many factors may contribute to these inconsistent findings, said Dr. Yang, including differences in study design, inclusion criteria, comparison groups, sample sizes, and countries where the research was carried out. Dr. Yang pointed out that many of these studies were done in the early stages of the pandemic or didn’t include older adults, the population most at risk for stroke.
The current study included 19,553 Medicare beneficiaries aged 65 years and older diagnosed with COVID-19 and hospitalized with acute ischemic stroke. The median age at diagnosis of COVID-19 was 80.5 years, 57.5% were women, and more than 75% were non-Hispanic Whites.
To ensure the stroke occurred after a COVID infection, researchers used a self-controlled case series study design, a “within person” comparison between the risk period and the control period.
They divided the study period (Jan. 1, 2019 to Feb. 28, 2021) into the exposure or stroke risk periods after the COVID diagnosis (0-3 days; 4-7 days; 8-15 days; and 15-28 days) and control periods.
Strokes that occurred 7 days before or 28 days after a COVID diagnosis served as a control period. “Any stroke that occurred outside the risk window is in the control period,” explained Dr. Yang.
He added that the control period provides a baseline. “Without COVID-19, this is what I would expect” in terms of the number of strokes.
To estimate the incidence rate ratio (IRR), investigators compared the incidence of acute ischemic stroke in the various risk periods with control periods.
The IRR was 10.97 (95% confidence interval, 10.30-11.68) at 0-3 days. The risk then quickly declined but stayed higher than the control period. The IRRs were: 1.59 (95% CI, 1.35-1.87) at 4-7 days; 1.23 (95% CI, 1.07-1.41) at 8-14 days; and 1.06 (95% CI, 0.95-1.18) at 15-28 days.
The temporary increase in stroke risk early after an infection isn’t novel; the pattern has been observed with influenza, respiratory infections, and shingles, said Dr. Yang. “But COVID-19 appears to be particularly risky.”
Although the mechanism driving the early increased stroke risk isn’t fully understood, it’s likely tied to an “exaggerated inflammatory response,” said Dr. Yang. This can trigger the cascade of events setting the stage for a stroke – a hypercoagulation state leading to the formation of blood clots that then block arteries to the brain, he said.
It’s also possible the infection directly affects endothelial cells, leading to rupture of plaque, again blocking arteries and raising stroke risks, added Dr. Yang.
The association was stronger among younger beneficiaries, aged 65 to 74 years, compared with those 85 years and older, a finding Dr. Yang said was somewhat surprising. But he noted other studies have found stroke patients with COVID are younger than stroke patients without COVID – by some 5 to 6 years.
“If COVID-19 disproportionately affects younger patients, that may explain the stronger association,” said Dr. Yang. “Stroke risk increases tremendously with age, so if you’re a younger age, your baseline stroke risk is lower.”
The association was also stronger among beneficiaries without a history of stroke. Again, this could be related to the stronger association among younger patients who are less likely to have suffered a stroke. The association was largely consistent across sex and race/ethnicities.
Dr. Yang stressed that the findings need to be confirmed with further studies.
The study was carried out before widespread use of vaccinations in the U.S. Once those data are available, Dr. Yang and his colleagues plan to determine if vaccinations modify the association between COVID-19 and stroke risk.
The new results contribute to the mounting evidence that a COVID-19 infection “can actually affect multiple human organs structurally or functionally in addition to the impact on [the] respiratory system,” said Dr. Yang.
Some dates of COVID-19 diagnoses may be incorrect due to limited test availability, particularly early in the pandemic. Another limitation of the study was possible misclassification from the use of Medicare real-time preliminary claims.
In a provided statement, Louise D. McCullough, MD, PhD, chair of the ISC 2022 and professor and chair of neurology, McGovern Medical School, University of Texas Health Science Center at Houston, noted that the study focused on older adults because it was examining Medicare beneficiaries.
“But everyone is likely at risk for stroke after COVID,” she said. “Any infection is linked to stroke risk, probably because any infection will cause inflammation, and inflammation can cause clots or thrombus, which is the cause of stroke.”
There was no outside funding for the study. No relevant conflicts of interest were disclosed.
A version of this article first appeared on Medscape.com.