UTRECHT, Netherlands — People are six times more likely to suffer a heart attack the week after having the flu than in the entire year before or after their illness, researchers explain. The new study analyzed data from more than 26,000 patients across the Netherlands to demonstrate the increased risk of attacks when suffering from influenza.
The virus has long been known to increase the “stickiness” in the blood which, along with inflammation, can weaken fatty plaques in the arteries and cause a clot. The research team, from The University Medical Center (UMC) Utrecht, hope their research will help underline the importance of vaccination and raise awareness of heart attack symptoms among flu patients.
Though the link between heart attacks – when the blood supply to the heart suddenly stops due to a blockage – and flu is not a new discovery, previous studies have only focused on individuals hospitalized for a heart attack. A Canadian study from 2018, for example, did not include information from death records, meaning scientists did not factor in deaths which occurred outside of hospitals.
In this study, however, the team from the Julius Center for Life Sciences and Primary Care at UMC Utrecht, used the results of tests from 16 labs across Holland — covering around two-fifths of the entire population, alongside death and hospital records to gain a more accurate and complete overview.
Across the Dutch laboratories, the team recorded 26,221 cases of influenza – an infection of the nose throat and lungs – between 2008 and 2019. Just over 400 of those with the flu had at least one heart attack within one year of their flu diagnosis. Of the 419 patients who had heart attacks, 25 suffered these in the first seven days after being diagnosed with the flu.
Another 217 suffered heart attacks within the year prior to their diagnosis, and 177 suffered theirs in the year following diagnosis but after the first week. Around a third of the individuals (139 of 401) died of any cause within a year of having the flu.
Dr. Annemarijn de Boer and the research team calculated that those they studied were 6.16 times more likely to suffer a heart attack in the first seven days after their flu diagnosis than in both the entire year preceding and following diagnosis.
The 2018 Canadian study had that figure at around 6.05 times. However, excluding the data from death records, as the previous Canadian study did, reduced the increased risk of heart attacks in the week following diagnosis to 2.42 times.
The Dutch researchers say this illustrates the impact that incomplete data can have on study findings. They add that differences in testing practices in the two countries may explain why they found the association between flu and heart attacks to be weaker than in the Canadian study. For example, testing people for flu outside of hospitals is less common in the Netherlands than in Canada. However, the association is still significant and, by using a similar method to the Canadian scientists, the UMC Utrecht team have been able to confirm the increased risk across different populations.
Along with the coagulation of the blood that influenza can cause, they believe inflammation also weakens fatty plaques that build up in the arteries. If one of these plaques ruptures, a blood clot can form, blocking the supply of blood to the heart and causing a heart attack.
“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,” says Dr de Boer, according to a statement from SWNS.
Dr de Boer and the team hope their study, reinforced by the previous Canadian study, will help emphasize the importance of methods such as vaccination to prevent flu infections – especially in older adults, who have a higher risk of hospitalization due to the flu.
“Our results endorse strategies to prevent influenza infection, including vaccination,” Dr de Boer adds. “They also advocate for a raised awareness among physicians and hospitalized flu patients for symptoms of heart attacks. While it isn’t clear from our results if those with less severe flu are also at risk, it is prudent for them to be aware of the link.”
The team is scheduled to present their findings at the European Congress of Clinical Microbiology & Infectious Diseases (ECCMID).
South West News Service writer James Gamble contributed to this report.