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Chances of a heart attack are increased six-fold during the first seven days after detection of laboratory-confirmed influenza infection, according to a new study by researchers at the University of Toronto.

“Our findings are important because an association between influenza and acute myocardial infarction reinforces the importance of vaccination,” says Dr. Jeff Kwong, associate professor of epidemiology and clinical public health at the Dalla Lana School of Public Health and lead author of the study.

In the study , the researchers found a significant association between acute respiratory infections, particularly influenza, and acute myocardial infarction, a heart attack.

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 immunization in those at high risk of heart attacks,” says Kwong, who is also an associate professor in the department of family and community medicine.

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 hospitalized 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 handwashing,” says Kwong (right), who is also a scientist at the  and 

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

The research was supported by the Canadian Institutes of Health Research, Public Health Ontario and by the Institute for Clinical Evaluative Sciences, which is funded by an annual grant from the Ontario Ministry of Health and Long-Term Care.