• Posted March 29, 2023

Flu Boosts Short-Term Odds for Heart Attack 6-Fold

Getting the flu isn't fun for many reasons, but it can also trigger a heart attack, a new study suggests.

A heart attack is six times more likely in the week after a person is diagnosed with flu than in the year before or after, according to Dutch researchers.

This emphasizes the need for flu patients and those caring for them to be aware of heart attack symptoms. It also underscores the importance of getting a flu shot, the authors said.

The findings are scheduled to be presented April 18 at a meeting of the European Congress of Clinical Microbiology and Infectious Diseases, online and in Copenhagen, Denmark.

“With the potential public health implications of an association between influenza virus infection and acute heart attacks, showing robustness of results in a different study population is important,” said researcher Annemarijn de Boer, of the Julius Center for Life Sciences and Primary Care at UMC Utrecht in the Netherlands.

“Our results endorse strategies to prevent influenza infection, including vaccination. They also advocate for a raised awareness among physicians and hospitalized flu-patients for symptoms of heart attacks," de Boer said in a meeting news release.

While the findings don't make it clear whether those with less severe flu are also at risk, de Boer said they should also be aware of the link.

While the connection between flu and heart attacks was also made in a 2018 Canadian study, it included only hospitalized people and not those who died of heart attacks elsewhere.

In this study, researchers relied on test results from 16 laboratories, covering around 40% of the Dutch population, along with death and hospital records.

More than 26,000 cases of influenza were confirmed by the labs between 2008 and 2019.

The researchers found that 401 individuals had at least one heart attack within a year of their flu diagnosis, with a total of 419 heart attacks.

Of the 419 heart attacks, 25 were in the first seven days after flu diagnosis; 217 in the year before diagnosis; and 177 in the year after flu diagnosis but not including the first seven days.

About one-third of the 401 patients died of any cause within a year of being diagnosed with flu.

The researchers calculated that the individuals studied were 6.16 times more likely to have a heart attack in the week following a flu diagnosis than in the year before or after. The Canadian study found they were 6.05 times more likely to have a heart attack in those seven days.

Excluding data from death records, as in the Canadian study, reduced the increase in heart attack risk in the first week to 2.42 times. Dutch researchers said this underscores the impact of incomplete data on study findings.

Researchers also said that differences in testing practices in the two countries may help explain the differences. It's less common to test for flu outside the hospital in the Netherlands than it is in Canada, according to researchers.

The Dutch researchers said the association is still significant and that they were able to confirm that the increase in risk applies across different populations.

The influenza virus is known to increase clotting of blood. This, along with the inflammation that is part of the body's immune response against the virus, can weaken fatty plaques that have built up in the arteries, the authors said. If a plaque ruptures, a blood clot can form, blocking the blood supply to the heart and cause a heart attack, they explained.

Findings presented at medical meetings are considered preliminary until published in a peer-reviewed journal.

More information

UCLA Health has more on the connections between heart disease and flu.

SOURCE: European Congress of Clinical Microbiology and Infectious Diseases, news release, March 28, 2023