People who receive a flu diagnosis are up to six times more likely to have a heart attack in the first week after testing positive than in the year before or after, according to a new study presented at the European Congress of Clinical Microbiology & Infectious Diseases.

Study details and key findings

According to Medscape, the current study builds on a 2018  study from Canadian researchers who found a strong association between the flu and heart attacks among patients who had been hospitalized for a heart attack.

In the current study, researchers from the Netherlands analyzed test results from 16 laboratories across the country, which covered around 40% of the population, as well as death and hospital records.

Overall, there were 26,221 laboratory-confirmed cases of influenza in the Netherlands between 2008 and 2019. Among patients with influenza, 401 people had at least one heart attack within a year of their flu diagnosis, with a total of 419 heart attacks in all.

Of these heart attack cases, 25 occurred within the first seven days of a flu diagnosis, 177 occurred in the year after, and 217 had occurred in the year before. Around a third of the patients who had heart attacks died of any cause within a year of their initial flu diagnosis.

After analyzing the data, the researchers found that patients were 6.16 times more likely to have a heart attack in the week after receiving a flu diagnosis compared to the year before or after — findings that were similar to the Canadian study.

However, after excluding deaths that occurred outside the hospital, the risk of a heart attack in the first week decreased to 2.42 times greater, though this number was still significant. According to the researchers, this decline may be due to the fact that flu testing and diagnosis is typically performed in the hospital, so the study's participants were more likely to have severe disease. Because of this, the findings may not necessarily apply to the general population.

Commentary

Mary Greene, a cardiologist at  Manhattan Cardiology who was not involved in the study, said that "[w]hile the methodology of this particular Dutch study did not yield as much robust data, the study certainly echoes previous studies that have come to similar conclusions."

"I do agree that a flu diagnosis can increase the odds of heart attack in a select group of patients, especially those with underlying heart disease," she added.

According to Greene, the increase in heart attacks among patients with the flu is likely due to the inflammatory process and other changes that occur in the body when it is fighting off illness. "Such inflammation in the body can make cholesterol plaques more vulnerable to rupture and blood more likely to clot, which is the underlying mechanism of both myocardial infarction (heart attack) and ischemic stroke," she said.

Separately, Sherif Mossad, an infectious disease physician at Cleveland Clinic, said the study's findings show that the flu can seriously impact people's health and is not just a mild inconvenience like some people may believe.

"[This study] raises more awareness about the seriousness and consequences of influenza," Mossad said. "It could precipitate serious, life-threatening problems." Mossad noted that other research has shown that influenza can worsen underlying conditions, such as multiple sclerosis, liver and kidney disease, and chronic obstructive pulmonary disease.

To reduce the risk of heart attacks, Greene recommends all people begin undergoing cardiovascular screenings starting at age 40, or potentially earlier if they have a history of early heart disease in their family.

"I also recommend that all patients with underlying coronary artery disease, history of stents, history of heart attack and history of heart failure have their annual flu shot," she said. "Cardiovascular patients see a larger benefit from influenza vaccination in terms of protection against a heart attack should they become infected with the influenza virus." (Frellick, Medscape, 4/17; Rudy, Fox News, 4/21)