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Is it just a flu? Watch for the increased risk of heart attack, stroke or sudden cardiac death

SINGAPORE — At 30 years old, Mr Lim Weifeng never felt more miserable in his entire life. What seemed like a common flu almost killed him in 2016 when the infection affected his heart.

To prevent flu-related complications such as viral myocarditis, heart attack or stroke, health experts stressed the importance of keeping chronic conditions under control and getting sufficient rest when one is unwell, regardless of one's age.

To prevent flu-related complications such as viral myocarditis, heart attack or stroke, health experts stressed the importance of keeping chronic conditions under control and getting sufficient rest when one is unwell, regardless of one's age.

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SINGAPORE — At 30 years old, Mr Lim Weifeng never felt more miserable in his entire life. What seemed like a common flu almost killed him in 2016 when the infection affected his heart.

He got to a hospital before things worsened but his heart was irreversibly damaged. He suffered from a condition known as viral myocarditis, which is an inflammation of the heart muscle.

Last year, he had a heart transplant to replace the damaged organ and now, he has to take medications for life and steers clear of crowded places to avoid getting infections.

Recalling the ordeal, the engineer, now 33, said that after an overseas trip, he came down with terrible body aches and a raging 39°C fever that did not let up even after taking paracetamol.

A week later, a new symptom emerged: He could not breathe properly.

“On top of the high fever, I had shortness of breath. I felt like I could not take deep breaths. Things didn’t seem right, so I went to the emergency department,” Mr Lim told TODAY.

At the hospital, scans showed that his heart was functioning at around a quarter of the normal rate of a healthy heart. He was found to have viral myocarditis.

Certain groups of people have a higher risk of getting myocarditis as a complication from a viral infection such as flu.

Assistant Professor Laura Chan, consultant at the department of cardiology of the National Heart Centre Singapore (NHCS), said that people at risk of flu-related complications are those with weakened immune systems, chronic diseases, and a Body Mass Index of over 40. People living in long-term care facilities, such as nursing homes, are also more vulnerable.

Mr Lim was not in those high-risk categories but viral myocarditis has been known to affect young people, including athletes. 

In Mr Lim’s case, the doctors did not confirm the exact virus that caused his flu-like symptoms and myocarditis.

He said: “Before this incident, I was fairly healthy and didn’t think my condition would be so serious. I was told I would likely not make it, and might have just collapsed somewhere, if I had waited a little longer to go to the hospital.”

Mr Lim spent more than two months in the Intensive Care Unit (ICU) of NHCS and for three weeks, he was hooked up to a life support machine.

To support his weakened heart, doctors implanted a mechanical pump known as a left ventricular assist device inside his chest.


With the next peak flu season returning at the end of the year, experts warned that the highly contagious infection — which spreads via coughing, sneezing and nasal secretions — could cause more than just a fever and pounding headache.

While most people who get the flu recover on their own, for some people, the common viral infection could be bad news for the heart. It could also be deadly.

Myocarditis is just one of many heart complications linked to the flu. The NHCS sees around 10 to 20 myocarditis cases each year.

Other flu-related cardiac complications include a heart attack, pericarditis (swelling of the pericardium, the thin sac-like membrane surrounding the heart), arrhythmias (abnormal heart rhythm), heart failure and sudden cardiac death.

Dr Yong Thon Hon, consultant at Changi General Hospital’s department of cardiology, said that there is compelling data associating respiratory infection epidemics with increased hospitalisation for cardiovascular-related events.

There is no well-defined flu season in Singapore but cases tend to peak in June and December. Professor Paul Anantharajah Tambyah, president of the Asia Pacific Society of Clinical Microbiology and Infection, said that this could be related to the school holidays when families travel and bring back different viruses from parts of the world, where seasonal flu occurs.

Dr Yong said that it is not uncommon to see flu patients with cardiovascular symptoms, particularly during the peak flu seasons. However, CGH does not track the exact number of cases, largely because there are “just too many”.

“Each year, thousands of flu patients present themselves to us with various cardiovascular symptoms, such as chest pain, palpitation, breathlessness, swollen legs, etc,” Dr Yong said.  

“Some of (the cardiovascular symptoms) are mild and patients fully recover with outpatient treatment. However, we have seen life-threatening cases that require advanced intensive care support.”

One particularly severe case Dr Yong saw was a woman in her 20s, who passed out at home after experiencing a week of flu-like symptoms.

“During her stay, she was critically ill with multi-organ failure, affecting her heart, brain, kidneys and liver. With optional mechanical support and multi-disciplinary care, she slowly turned the tide,” Dr Yong said.  

“Do remember the flu can potentially kill and sometimes, it can kill quickly.”

Warning signs of a worsening respiratory infection include a persistent fever of over 38.5°C for three or more days, breathing difficulties, chest pain, difficulties in swallowing, confusion, coughing blood and low blood pressure.


In a study of nearly 2,000 people aged 40 and above in Scotland, those who had a confirmed respiratory infection such as the flu or pneumonia were six times more likely to suffer a heart attack or stroke in the following three days.

The same study showed that around two in 10,000 people aged 75 years and above have a heart attack each week. In their analysis, researchers found that the figure rose to 10 in 10,000 in the week after patients have a respiratory infection.

Lead researcher Charlotte Warren-Gash from the London School of Hygiene and Tropic Medicine said that the heightened risk of a heart attack and stroke lasted around a week and a month respectively after the infection.

She said: “In general, respiratory infections are thought to increase the risk of heart attack and stroke by causing inflammation, which can lead to the development of blood clots.”

The influenza virus and Streptococcus pneumoniae, the most common pneumonia-causing bacteria, can also have harmful effects on heart muscle. 

That said, the risk of heart attacks and strokes after a respiratory infection is still low for young, healthy people, she added.

Associate Professor Warren-Gash specialises in epidemiology and was in Singapore last month to speak on flu-related cardiovascular complications at the 10th edition of the Options for the Control of Influenza (Options X) Conference. 

New Singapore research also highlights the potentially deadly effects of respiratory infections.

In a study here published last year in peer-reviewed journal BMC Infectious Diseases, it found that out of 117 patients requiring ICU support for severe community-acquired pneumonia, 16 of them died.

The study’s lead author Jessica Quah said that influenza A, one of the common types of flu virus, was identified in around 24 per cent of the 117 patients, while the most common bacteria, Streptococcus pneumoniae, was found in about 16 per cent of the 117 patients.

Dr Quah, a consultant at CGH’s department of respiratory and critical care medicine, said: “Having a concurrent viral and bacterial infection was a risk factor for dying. Both Influenza A and Streptococcus pneumoniae may be effectively prevented with vaccination.”


Experts told TODAY that getting an annual flu jab could prevent flu-related complications.

Assoc Prof Warren-Gash said: “Vaccination can prevent complications by preventing you from getting the flu in the first place. If you are vaccinated and still get flu, the illness is likely to be milder so the chance of complications is lower.”

An interesting finding from her study: Heart attack and stroke risk after respiratory infections appeared greater among adults under the age of 65 than in the older age group.

She said that this could be because vaccine uptake was higher among those over 65, and being vaccinated could help protect against heart attacks and strokes after respiratory infection.

Prof Tambyah, who chaired the scientific committee for the Options X conference, said that flu vaccines are not 100 per cent effective.

“The (flu) strains contained in the current vaccine are the results of a prediction by experts at the World Health Organization on what would be the dominant circulating strains in the coming months.

“When the prediction is right, the vaccine significantly reduces illness, hospitalisation and complications. When there is a mismatch, it is possible that someone who has been vaccinated will get the flu and obviously, the effectiveness is much lower,” he explained.  


To prevent flu-related complications, health experts stressed the importance of keeping chronic conditions under control and getting sufficient rest when one is unwell. This applies to both the young and old.

“When we are sick, our immune system is weakened and the body is informing us that we need rest.

“Exercise or over-exertion is a form of physical stress that prevents the immune system from recovering. Listening to your body will improve the recovery process,” Assoc Prof Chan said. 

Explaining why “sweating out” a fever is not advisable, Dr Quah said: “When a person is ill with fever or flu, the body’s basal metabolic rate and heart rate are increased. To be able to engage in exercise, the heart will need to pump extra hard.

“This ability may be impaired during acute illness, hence the person may feel short of breath and easily tired when exercising.”

Dr Quah also cautioned exercise enthusiasts and athletes against exercising if there are symptoms of fever, chest tightness, chest pain, fast heart rate or generalised muscle aches. It is best to wait until the symptoms resolve for at least 24 hours, and to stay well-hydrated before starting slow with five to 10 minutes of exercise.

Simple habits, such as covering up with a tissue or mask when coughing or sneezing, and staying away from crowded areas when one is ill, can also stem the spread of flu.

Prof Tambyah said: “When someone in the office starts coughing and sneezing, it is a matter of time before everyone else does.

“At a societal level, individuals should make sure they stay at home when they are sick and not go to work to infect other people. The scourge of ‘presenteeism’ is something we really want to eradicate in Singapore for good public health.”

Related topics

flu heart disease myocarditis stroke Health medical death

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