MIAMI: Coming down with the flu, bronchitis or pneumonia can dramatically raise the risk of a heart attack -- up to 17-fold -- in the days and weeks following the infection, researchers said Monday.

The findings confirm earlier research that pointed to an apparent link between respiratory infection and cardiac crises, scientists at the University of Sydney reported.

"A respiratory infection can act as a trigger for a heart attack," said senior author Professor Geoffrey Tofler.

"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."  

The study, published in the Internal Medicine Journal, was based on 578 patients who suffered a heart attack due to a coronary artery blockage.

Patients were asked about their activities before having a heart attack, including if they experienced a recent "flu-like illness with fever and sore throat", or of they had been diagnosed with pneumonia or bronchitis, said the report.

Seventeen percent of patients reported symptoms of respiratory infection within one week of the heart attack, and 21 percent within 31 days.

"Possible reasons for why respiratory infection may trigger a heart attack include an increased tendency towards blood clotting, inflammation and toxins damaging blood vessels, and changes in blood flow," said Tofler.

"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," he added.

"Don't ignore symptoms that could indicate a heart attack."        

Symptoms may include shortness of breath, pain and pressure in the chest and arms, nausea, dizziness or breaking out in a cold sweat.

Heart attacks tend to happen most often during the winter, and could be linked to the seasonal rise in flu and other respiratory infections, researchers said.