Two new studies have found a link between the flu and an increased risk of two serious conditions: stroke and rupture of the neck arteries.
The studies both used a database of patient records in New York state to examine whether having flu-like symptoms — such as fever, cough, body aches and fatigue — was tied to an increased risk of either stroke or a condition called "cervical artery dissection" (CAD). The latter condition occurs when there is a tear in one of the arteries of the neck, and this tear allows blood to leak into the layers of the artery wall. CAD itself is tied to an increased risk of stroke.
In the first study, researchers from Columbia University's Vagelos College of Physicians and Surgeons analyzed data from nearly 31,000 people who were hospitalized with an ischemic stroke in 2014. (An ischemic stroke is a stroke caused a blockage in blood flow to an area of the brain.) The study found that having flu-like symptoms increased the overall likelihood of having stroke by about 40 percent over the next 15 days.
In the second study, researchers from the same institution looked at data from about 3,800 people who had CAD between 2006 and 2014. These patients, the researchers found, were about 50 to 60 percent more likely to have had a flu-like illness in the month before their CAD was diagnosed, compared with the same time period in the years before their CAD diagnosis.
The findings suggest that "flu-like illnesses may indeed trigger [cervical artery] dissection," study lead author Madeleine Hunter, a second-year medical student at the College of Physicians and Surgeons, said in a statement.
(The studies looked at flu-like illness, rather than confirmed flu cases, because people with the flu often do not get their diagnosis officially confirmed with a lab test. This means that, in the health records system, there are many more reported cases of flu-like illness than confirmed flu.)
Both studies will be presented next week at American Stroke Association's International Stroke Conference 2019 in Honolulu; neither has been published in a peer-reviewed journal
Previous studies have also found a link between the flu and an increased risk of developing heart problems, including having a heart attack.
The reason for the link between flu-like illness and stroke or CAD is not known, and should be investigated in future studies. The risk could be related to inflammation in the body caused by the flu, the researchers said.
Still, it's important to note that the studies only found an association between flu-like symptoms and stroke and CAD, and cannot prove that the flu causes these conditions.
But overall, the findings highlight the importance of getting a flu shot, said Dr. Philip Gorelick, professor at Michigan State University's Department of Translational Science and Molecular Medicine, who was not involved in the study and has researched stroke prevention.
"I think people should consider [getting] a flu shot," Gorelick said in a video interview with the American Stroke Association, which is a division of the American Heart Association. Gorelick added that some studies have found a link between getting a flu shot and a reduced risk of stroke, which is "good news."
Originally published on Live Science.
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Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.