Flu increases heart attack risk six times: study

People with influenza may have a six-fold increased risk of experiencing a heart attack, particularly in the first seven days, according to a study which emphasises the importance of vaccination.

Chances of a heart attack are increased six times during the first seven days after detection of laboratory-confirmed influenza infection, said researchers at the Institute for Clinical Evaluative Sciences (ICES) and Public Health Ontario (PHO) in Canada.

"Our findings are important because an association between influenza and acute myocardial infarction reinforces the importance of vaccination," said Jeff Kwong, a scientist at ICES and PHO and lead author of the study.

In the study published in the New England Journal of Medicine, the researchers found a significant association between acute respiratory infections, particularly influenza, and acute myocardial infarction.

The risk may be higher for older adults, patients with influenza B infections, and patients experiencing their first heart attack.

The researchers also found elevated risk - albeit not as high as for influenza - with infection from other respiratory viruses.

"Our findings, combined with previous evidence that influenza vaccination reduces cardiovascular events and mortality, support international guidelines that advocate for influenza immunisation in those at high risk of a heart attack," said Kwong.

The researchers looked at nearly 20,000 Ontario adult cases of laboratory-confirmed influenza infection from 2009 to 2014 and identified 332 patients who were hospitalised for a heart attack within one year of a laboratory-confirmed influenza diagnosis.

"People at risk of heart disease should take precautions to prevent respiratory infections, and especially influenza, through measures including vaccinations and hand-washing," said Kwong.

The researchers said that patients should not delay medical evaluation for heart symptoms particularly within the first week of an acute respiratory infection.