New research conducted at the University of Sydney in Australia found that the risk of having an acute myocardial infarction, commonly referred to as a heart attack, is 17 times higher in the seven days following a respiratory tract infection.

The study, “Triggering of acute myocardial infarction by respiratory infection,” was published in the Internal Medicine Journal.

According to the research team, this is the first study of its kind to find an association between respiratory infections such as pneumonia, influenza and bronchitis, and the risk of heart attack.

The study enrolled 578 patients with angiography-confirmed heart attacks due to coronary artery blockage. Participants were questioned regarding recent symptoms of respiratory infection including sore throat, cough, fever, sinus pain, flu-like symptoms, or if they had a confirmed diagnosis of pneumonia or bronchitis.

Exposure to respiratory infection prior to the onset of heart attack was then compared against the usual frequency of exposure in the past year.

Interestingly, the researchers found that 17% of patients reported symptoms consistent with a respiratory infection within seven days before the heart attack, and 21%  of patients reported respiratory symptoms within 31 days of the heart attack.

“Our findings confirm what has been suggested in prior studies that a respiratory infection can act as a trigger for a heart attack,” Geoffrey Tofler, MD, the study’s senior author said in a press release. Tofler is a professor and cardiologist at University of Sydney, Royal North Shore Hospital and Heart Research Australia.

“The data showed that the increased risk of a heart attack isn’t necessarily just at the beginning of respiratory symptoms, it peaks in the first [seven] days and gradually reduces but remains elevated for one month.” Tofler added.

A secondary analysis limited to patients who reported only milder upper respiratory tract infection symptoms also was conducted and revealed an increased risk of heart attack by 13%.

“Although upper respiratory infections are less severe, they are far more common than lower respiratory tract symptoms. Therefore it is important to understand their relationship to the risk of heart attacks, particularly as we are coming into winter in Australia,” Tofler said.

Tofler believes that ”possible reasons for why respiratory infection may trigger a heart attack include an increased tendency toward blood clotting, inflammation and toxins damaging blood vessels, and changes in blood flow.”

The team concluded that future research is needed to develop improved treatment strategies, particularly for patients who are at an increased risk of heart attack.

“Our message to people is while the absolute risk that any one episode will trigger a heart attack is low, they need to be aware that a respiratory infection could lead to a coronary event. So consider preventative strategies where possible, and don’t ignore symptoms that could indicate a heart attack.” Tofler concluded.