Lab-Confirmed Flu Virus Linked to Imminent Risk for Acute MI

Patients with laboratory-confirmed influenza were about six times as likely to be admitted for acute MI in the following 7 days compared with the period comprising the prior and subsequent years, results of a cohort study show.[1]

The risk was especially pronounced in older patients and was independent of flu vaccination status or history of MI hospitalization. There was also a signal that other forms of respiratory infection can similarly raise the risk for MI admission.

The findings are consistent with a lot of prior research, acknowledged Dr Jeffrey C Kwong (University of Toronto, ON), but much of it associated MI with acute respiratory infections by undetermined pathogens, or with other indirect indicators of flu.

“This is the first one where we used lab-confirmed influenza as the exposure, and we found this association that was quite strong between influenza and MI,” he told | Medscape Cardiology.

Kwong is lead author on the study, which was based on Ontario health insurance records of people tested for respiratory viruses from May 2009 to May 2014 and was published January 24 in the New England Journal of Medicine.

The results are “no surprise,” agreed Dr Scott David Solomon (Brigham and Women’s Hospital, Boston, MA), who wasn’t involved in the study. But, he added, “What’s novel here, and improves on prior knowledge, is that it goes down to the individual-patient level, and says that when somebody actually has confirmed influenza, that they are more likely to have an MI.”

Kwong and his colleagues state that the increased MI risk regardless of vaccination status should not be seen as evidence that influenza vaccinations are ineffective; the study wasn’t designed to explore that issue. It does suggest, however, “that if vaccinated patients have influenza of sufficient severity to warrant testing, their risk of acute myocardial infarction is increased to a level that is similar to that among unvaccinated patients.”

The study seems to strengthen familiar public health messages about getting flu vaccinations and taking measures to prevent the spread of respiratory viruses, especially for patients with cardiovascular risk factors. Despite such messages, vaccination rates may be low even in such high-risk groups.

Solomon pointed to a recent analysis based on patients with heart failure in the PARADIGM-HF trial that saw only about a 53% rate of vaccination for influenza in North America.[2]

“And that was surprising because these were people who are clearly at risk, and would clearly benefit from vaccination,” he said.

Even when the effectiveness of the season’s flu vaccination has been questioned, such as the current flu season, “getting some protection is better than getting no protection,” Kwong said.

Secondary prevention patients with heart disease “don’t question taking aspirin, they don’t question taking β-blockers, they don’t question taking blood pressure medications or statins. But a lot of patients question the value of getting a flu shot,” he said.

“If you compare the effectiveness of influenza vaccination in preventing infection to statins in preventing MI, they shouldn’t be having second thoughts about getting a flu shot.”

Seven-Day Risk Interval

The analysis looked at 364 hospitalizations for acute MI in 332 patients that occurred within 1 year before and 1 year after laboratory confirmation of influenza; 48% in were women and 24% of the patients had been previously hospitalized for MI.

Of the 364 hospitalizations, 20 occurred during the first 7 days after the collection of a positive respiratory specimen, termed the “risk interval.” The remaining 344 hospitalizations occurred during the 2-year period made up of the year before and the year after the risk interval, termed the “control interval.”

The risk for MI hospitalization was increased sixfold during the risk interval compared with the control interval. Kwong said the group had expected the risk to fall off gradually, “but we actually saw that it just dropped down to nothing right after the first week. It’s really that first week where the risk is concentrated.”

Table 1. Incidence Ratios for Acute MI Hospitalization by Time After Laboratory Confirmation of Influenza

Interval Incidence Ratio (95% CI)
Days 1–7 6.05 (3.86–9.50)
Days 1–3 6.30 (3.25–12.22)
Days 4–7 5.78 (3.17–10.53)
Days 8–14 0.60 (0.15–2.41)
Days 15–28 0.75 (0.31–1.81)


The group also observed increased MI hospitalization risk associated with respiratory samples positive for viruses other than influenza. The implication may be that respiratory infections per se, not simply influenza, are associated with acute MI, according to Kwong.

“I think we just found that influenza risk seemed to be higher than that of the other respiratory viruses.”

Risk associated with influenza B was higher than with influenza A; Kwong said his group doesn’t have an explanation for the difference.

Table 2. Incidence Ratios for Acute MI Hospitalization by Specific Infections

Infection Incidence Ratio (95% CI)
Influenza A 5.17 (3.02–8.84)
Influenza B 10.11 (4.37–23.38)
RSV 3.51 (1.11–11.12)
Noninfluenza virus, non-RSV 2.77 (1.23–6.24)
Illness, no respiratory virus identifieda 3.30 (1.90–5.73)
RSV = respiratory syncytial virus. aFrom among influenza A, influenza B, RSV, parainfluenza virus, adenovirus, human metapneumovirus, coronavirus, or enterovirus.


Respiratory infections could trigger MI by any of several possible mechanisms, Kwong and Solomon observed.

Influenza elevates an array of proinflammatory cytokines that can lead to endothelial dysfunction, and possibly plaque rupture, but whether that’s the primary mechanism “is really just a postulate. We don’t know for sure that’s what is contributing,” Solomon said.

People with the flu also have increased oxygen demand, which might produce myocardial ischemia in someone with significant coronary lesions, he observed. Platelet activation is also increased.

“If the flu can trigger these events in people who are at risk, then it behooves us to do everything we can to minimize the risk associated with influenza,” Solomon said. “Obviously that means vaccination. And we are currently testing a strategy that might provide even better immunity in patients who are at risk.”

Solomon is a principal investigator for the ongoing Influenza Vaccine to Effectively Stop Cardiothoracic Events and Decompensated Heart Failure (INVESTED) trial, which has randomly assigned about 3000 of an estimated target of 9300 patients, he said.

INVESTED is comparing a high-dose trivalent influenza vaccine to a quadrivalent vaccine at a standard dose in patients with a recent history of hospitalization for MI or heart failure and other high-risk features. Mortality and cardiopulmonary hospitalization are the primary endpoints.

How long do cold and flu germs stay alive after infected people cough and sneeze all over everything?

It varies, depending partly on where the germ-laden droplets fall. Experiments with specific cold and flu germs have shown potential survival times ranging from a few minutes to 48 hours or more. How long such germs remain capable of infecting you in day-to-day life is harder to say.

Germs generally remain active longer on stainless steel, plastic and similar hard surfaces than on fabric and other soft surfaces. Other factors, such as the amount of virus deposited on a surface and the temperature and humidity of the environment, also have effects on how long cold and flu germs stay active outside the body.

It’s easy to catch the flu or a cold from rubbing your nose after handling an object an infected person sneezed on a few moments ago. But personal contact with an infected person — a handshake, for example — is the most common way these germs spread.

The best way to avoid becoming infected with a cold or flu virus is to wash your hands frequently with soap and water or with an alcohol-based sanitizer. Also avoid rubbing your eyes or biting your nails. Most importantly — get a flu vaccine every year.

Are men unfairly castigated for having “man flu” and running to their sick beds at the merest sign of a sniffle?

Man sneezing on a busHe will be in bed soon with a damp towel on his brow…

Research suggests that women are at greater risk of getting flu than men because they tend to spend more time around children, who are more likely to have a flu-like illness in the first place.

A nationwide flu survey carried out by London School of Hygiene and Tropical Medicine during last winter found that women were 16% more likely to say they had flu symptoms.

So is it really women who are making all the fuss about being unwell?

This winter, the online flu survey is up and running again and aiming to find out the answer.


The survey needs people of all ages around the country to report any flu-like symptoms by filling in an online questionnaire.

This data will be used to map the spread of flu across the country during the winter.

Researchers can then analyse how the virus spreads and who it affects.

How ill?

Dr Alma Adler, who runs the project, says they wanted to find out more about gender differences and flu in this year’s survey.

“We haven’t found any evidence of ‘man flu’ yet.

“The biggest risk factor is having children under the age of 18 and for this reason women are more at risk of flu.

“This year we have included some new questions, such as ‘How bad do you feel?’

“People can answer on a number scale of one to 10.”

What is flu?

How an influenza virus particle might look
  • Flu is a respiratory illness linked to infection by the influenza virus.
  • Symptoms usually include headache, fever, cough, sore throat, aching muscles and joints.
  • Influenza occurs most often in winter and usually peaks between December and March.
  • The virus was first identified in 1933.
  • There are two main types that cause infection: influenza A and influenza B
  • New strains of the virus are constantly emerging, which is why the flu vaccine should be given each year.

This is the crucial part, asking people how they feel when they have flu, by delving into the psychology of illness – not just the science.

‘More sensitive’

And that could help scientists discover if men and women experience flu differently.

John Oxford, professor of virology at Queen Mary, University of London, says there is no scientific evidence for “man flu” but there is a difference in behaviour.

“We know that women react differently to infection. They are more sensitive to their health. Men bluster around a bit.

“So there are differences in how men and women perceive illness and then differences in behaviour.

“Men think they are going to die when they are unwell, so they go to bed and expect women to look after them.”

Dr Douglas Fleming, from the Royal College of GPs’ flu research unit, says there is no rule when it comes to how flu viruses affect people.

“Every flu virus is different. It depends on the strain. We don’t know ahead of time how it will affect people.

“Different viruses affect men, women and children differently.”

Weaker sex

Previous research from the University of Cambridge came to a different conclusion.

It found evidence that women were better at fighting infections than men.

Man getting the seasonal flu jabThe over-65s are among those entitled to a free flu jab

Evolutionary factors and hormonal differences were thought to make males more susceptible to infection than females.

In the animal world too, across a range of species, males tend to be the “weaker sex” in terms of immune defences, the Cambridge research team said.

This would back up the argument that “man flu” exists because men would be more susceptible to viruses and therefore more likely to be unwell.

But if children are the main sufferers and harbourers of influenza, spreading it to their parents and grandparents, then won’t mothers automatically be in the firing line?

Prof Oxford says men will still be infected just as much.

“If the parents are sleeping together in the same bed, spending at least eight hours in the same room sharing pillows, then the flu virus will soon move on to the husband.”


The Health Protection Agency (HPA) started its weekly monitoring of flu activity in the UK population in October.

So far this winter, the number of people with flu symptoms going to see their GP is low (6.9 per 100,000 in England).

This could explain why just 65% of those aged over 65 and 32% of pregnant women have taken up the offer of a flu vaccine.

Dr Richard Pebody, head of seasonal flu surveillance at the HPA, said they are hoping this winter will mirror last winter’s trend.

“The 2011/2012 flu season was one of the lowest on record – following two years of high flu activity, including the 2009 flu pandemic. This demonstrates how unpredictable the flu season can be.”

Whether you are a man or a woman, there is a chance you could be infected by the flu virus in the coming months.

If you are in any of the “at risk” groups, the key is to be protected in advance by getting the flu jab.

Then keep a box of tissues and a hot water bottle handy.