The Grapevine

Flu Can Increase Heart Attack, Stroke Risk, Study Claims

Those who have suffered flu or pneumonia may be six times more likely to experience heart attack or stroke over the days following the infection. A new research was published in the European Respiratory Journal, and emerged from the largest study to examine the risk of heart disease and stroke due to respiratory infections. 

"Heart disease, strokes, and lower respiratory infections have been the three leading causes of death globally for over 15 years, and are important public health problems that affect large numbers of people worldwide," explained lead researcher Dr. Charlotte Warren-Gash, Associate Professor of Epidemiology at the London School of Hygiene & Tropical Medicine. 

The study shed light on how inflammation, caused by respiratory infections, can eventually lead to blood clots which are believed to increase the risk of heart attack and stroke. Heart function is also disrupted by S.pneumoniae, the bacteria commonly known to cause pneumonia.

As part of the study, researchers examined national infection surveillance data from the Scottish Morbidity Record. An analysis identified 1,227 adults, who had their first heart attack, and 762 adults, who had their first stroke, in the past decade, also had a respiratory virus or bacterial infection at sometime between 2004 and 2014.

Among people aged 75 or older in Scotland, two in 10,000 people have a heart attack each week. In their analysis, the researchers found the figure rose to 10 in 10,000 in the week following a respiratory infection. Organisms like S.pneumoniae bacteria and influenza were found to have the biggest hand in increasing the risk. 

Similar research conducted in Canada revealed a six-fold increase in the risk of heart attacks during the first seven days of lab-confirmed influenza.

In terms of limitations, the study did not look at individual effects of less common respiratory infections. The researchers acknowledged the risk of heart attacks and stroke after a respiratory infection is higher among those over 65 and is lower in younger people. Apart from age factors, those with pre-existing heart conditions were also said to be at risk.

Dr. Warren-Gash explained having more than one medical condition becomes a consequence of aging, making it even more important to understand the association between various diseases. She added knowing who is at risk of cardiovascular complications after respiratory infections can help professionals intervene and prevent them, typically through methods such as vaccination. 

Abundant reports suggested the flu shot not only protected people from influenza but also reduced the risk of heart attack and stroke. 

"Our research highlights the importance of ongoing work into which doses of vaccine are best to protect people from heart attacks and strokes," Dr. Warren-Gash added. "Although flu and pneumonia seem to have the biggest impact, this research also shows that a group of other respiratory viruses had some triggering effects. We don't currently have vaccines for these viruses so further research is needed."