Two new research studies show that the chance of experiencing a stroke are significantly higher after flu or flu-like illness.

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Researchers are looking for a link between flu-like illness and the risk of stroke.

Each year, nearly 800,000 people in the United States experience a stroke.

The risk factors include weight, smoking status, age, and family history of stroke.

However, flu and flu-like illnesses could join this list, according to research due to be presented at the International Stroke Conference in Honolulu, HI, next week.

In fact, the theory that flu or flu-like infections may raise the risk of stroke is not new.

In 2015, Medical News Todayreported that children are six times more likely to experience a stroke if they had an infection — mostly upper respiratory infections — during the previous week.

In 2018, a study that appeared in the European Respiratory Journal looked at the medical records of 762 people living in Scotland who had experienced a stroke. The researchers found an increased risk of stroke in the 28 days after infection with respiratory viruses.

While these studies have been relatively small, new research by a team from Colombia University in New York City, NY, is the biggest of its kind to date.

Risk of stroke higher for up to 1 year

The scientists looked at the medical records of 30,912 individuals from the 2012–2014 inpatient and outpatient New York Statewide Planning and Research Cooperative System who had been admitted to the hospital with ischemic stroke in 2014.

They then searched for any incidences of hospitalization as a result of flu-like illness in the 2 years before the stroke.

What they found was a nearly 40 percent increase in the odds of having a stroke within 15 days of being admitted to the hospital with flu-like symptoms. Overall, the risk of experiencing a stroke was, in fact, increased for up to 1 year.

Interestingly, people living in rural areas were just as likely to be affected, which came as a surprise to the research team.

"We were expecting," explains lead study author Amelia K. Boehme, Ph.D., an assistant professor of epidemiology in neurology for Vagelos College of Physicians and Surgeons at Columbia University, "to see differences in the flu-stroke association between rural and urban areas."

"Instead we found the association between flu-like illness and stroke was similar between people living in rural and urban areas, as well as for men and women, and among racial groups."

Amelia K. Boehme, Ph.D.

The reason for the link between flu-like illness and stroke is still unclear. Yet inflammation caused by the culprit responsible for the flu-like infection might be to blame, according to the authors.

Flu and neck artery tears

A further piece of evidence linking flu-like infections to an increased risk of experiencing a stroke is also due to be presented at the International Stroke Conference next week.

Madeleine Hunter, also from Vagelos College of Physicians and Surgeons at Columbia University, reviewed 3,861 medical cases of first nontraumatic cervical artery dissection within the New York State Department of Health Statewide Planning and Research Cooperative System (2006–2014).

During a neck artery tear, or cervical artery dissection, a part of the lining of an artery in the neck tears. This results in narrowing of the space, restricting or stopping blood flow. Cervical artery dissection is a known risk factor for stroke, particularly in those aged 15–45.

Along with her colleagues, Hunter revealed that nearly half of the people they reviewed also had experienced a flu or flu-like illness in the 3 years before the arterial tear.

However, the most common time for a flu-like infection was up to 30 days before the cervical artery dissection.

"Our results suggest that the risk of dissection fades over time after the flu. This trend indicates that flu-like illnesses may indeed trigger dissection," she explains.

Dr. Philip B. Gorelick, a professor of translational science and molecular medicine at Michigan State University College of Human Medicine in Grand Rapids, comments on the findings of both studies.

According to him, "If you do have the flu and you start having other symptoms that are consistent with stroke, such as weakness of the face, arm, or leg on one side or both, trouble speaking, slurred speech, loss of vision in one or both eyes, the worst headache of your life, or staggering around, you could have a dissected artery or some other cause of stroke."

He adds, "I think people should consider taking a flu shot."