Flu Can Trigger Heart Attack, Stroke

Getting the flu could increase your risk of having a heart attack or stroke, but getting a flu shot probably won’t.

The findings come from a new study examining the relationship between a current infection and heart disease risk.

Researchers from the London School of Hygiene and Tropical Medicine report that heart attack and stroke risk rose sharply among study participants during the first few days following the diagnosis of influenza, pneumonia, bronchitis, and other respiratory tract infections. A less-pronounced increase in risk was seen among people who had urinary tract infections. However, getting a flu shot or other vaccination did not appear to increase risk.

The study offers some of the first clinical evidence of a direct association between current infection and the inflammation it creates and cardiovascular risk.

“There has been a lot of anecdotal evidence suggesting that acute infection can help trigger heart attack and stroke,” researcher Liam Smeeth, PhD, tells WebMD. “But ours is certainly the largest study to show this association.”

The Inflammation Link

There is growing evidence that chronic inflammation plays a role in atherosclerosis, a key factor in heart attack and stroke risk. However the cardiovascular impact of transient inflammation, such as that seen during an infection, has not been extensively studied. Being vaccinated against illnesses such as flu, pneumonia, and others also causes inflammation to occur, but to a lesser extent.

In an effort to determine what, if any, role short-term inflammation plays in heart attack and stroke risk, Smeeth and colleagues looked at the medical records of roughly 20,500 cases of first-time heart attack victims and 19,000 first-time stroke patients. They analyzed the risk of these heart disease-related events after vaccinations and commonly occurring infections.

Their findings are reported in the Dec. 16 issue of the New EnglandJournal of Medicine.

The researchers reported no increase in the risk of cardiovascular events among people who received vaccinations to prevent flu, tetanus, or pneumonia and meningitis.

The cardiovascular disease risk was greatly elevated, however, among people suffering from respiratory tract infections.

A fivefold increase in heart attacks and a threefold increase in strokes were reported during the first three days following the diagnosis of a respiratory infection. The risk declined over time, and was almost back to normal within one to three months of recovery from the illness. A smaller increased risk of heart disease-related events was also seen among patients with urinary tract infections.

Heart Attack, Stroke Risk Is Small

Recent research shows high-risk people can lower their risk of heart attack, stroke, and death by getting a flu shot. The U.K. study’s findings offer reassurance to people who take that advice, Smeeth says.

“This certainly reinforces the notion that people at high risk should be vaccinated against the flu and that they should do everything else they can to protect themselves,” he says.

American Heart Association past president Valentin Fuster, MD, adds that while the new findings offer the best evidence yet of a link between infection-related illness and cardiovascular events, it is important not to scare people unnecessarily. Fuster studies inflammation and heart disease as director of the Cardiovascular Institute at Mount Sinai School of Medicine in New York.

“This study shows that acute infection can trigger heart attack and stroke, but it is important to remember that the risk is very small,” he says. “People should not think that they are going to have a heart attack if they get a cold or the flu.”

By Salynn Boyles, reviewed by Brunilda Nazario, MD

SOURCES: Smeeth, L. The New England Journal of Medicine, Dec. 16, 2004; vol 351: pp 2611-2618. Liam Smeeth, PhD, department of epidemiology and population health, London School of Hygiene and Tropical Medicine, London. Valentin Fuster, MD, past president, American Heart Association; director, Cardiovascular Institute, Mount Sinai School of Medicine, New York City.