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Flu shots are generally grown in an egg base. ((Reuters))

Each flu season, usually from October to March, the disease cuts a swath through workplaces, schools and hospital emergency rooms.

Yet despite its big impact, the flu is poorly understood by most Canadians. We think of it as a nuisance, like the snow. But it's much more than that.

Here are the top 10 misconceptions about seasonal flu.

1. No one ever died from the flu.

Wrong. Although statistically the flu is unlikely to kill young, healthy individuals, it's still the leading infectious cause of hospitalization and death in Canada. That's because it attacks and weakens the elderly and the ill people with heart and lung conditions, diabetes, kidney disease, HIV and cancer. The flu or complications from the flu kills between 4,000 and 8,000 Canadians a year, depending on the severity of the season, according to the Public Health Agency of Canada.

The estimates are based on mathematical models. More people seem to die during the winter than in the summer and some of the deaths are attributed to influenza, said Dr. Michael Gardam of the Ontario Agency for Health Protection and Promotion.

2. For most people it's not a serious illness.

That depends how you define serious. It makes about five million Canadians sick every year that's one in every six of us. If you're one of the unlucky, you can count on being off work for as much as a week and feeling pretty lousy for much longer than that, perhaps up to a month. About 1.5 million workdays are lost each year and the estimated cost to the Canadian system in terms of health-care costs and lost productivity is a cool $1 billion.

3. I've had the flu three times this year.

Fortunately, that's just not the case. What you've probably had is a cold, or repeated colds most people can expect to get two to four of them a year. Here's what sets the flu apart from the common cold:

  • It comes on suddenly. While the total incubation period is usually about two days, you can go from feeling perfectly fine to death warmed over in a matter of hours. That's because the flu virus is a profligate little bug. "It replicates in just four hours," says Dr. Danuta Skowronski, a physician epidemiologist with the B.C. Centre for Disease Control.
  • You have a fever. With a cold, you may be sneezing and uncomfortable, but your temperature isn't likely to rise. With the flu, the alternating fever and chills may make you feel as though your body's thermostat has gone completely wacky.
  • You're exhausted. "The technical term is 'prostration'," says Skowronski. "What that means is flat-out fatigue." With a cold you feel as though you can carry on. With the flu, you just want to crawl into bed.

4.I can't have the flu I'm not nauseated.

Contrary to common belief, stomach and intestinal complaints aren't generally a feature of the flu, except in small children. "The flu is a respiratory illness," says Skowronski, "and the lungs are the major site of symptoms." You might be surprised to learn that the virus doesn't even spread throughout your body. Your headache, fever and aching muscles are actually an inflammatory response; that is, your body is working overtime to try to kill off the virus in your lungs. A small number of people (fewer than 10 per cent) may have some intestinal problems with the flu, but that's not the main feature of the bug. If you were nauseated and vomiting, it's far more likely you had food poisoning or gastroenteritis. As for the term "stomach flu," well, there's no such thing.

5. I'm so sick I need a doctor!

Unless you're elderly or have other health problems, resist the urge to see your doctor. Antibiotics are powerless in the face of the flu virus, and you'll only be spreading your germs to others in the waiting room. Dr. Louise Sourisseau, a family practitioner in Richmond, B.C., says that during flu season, somewhere between five and 10 per cent of her patients are suffering from the flu. "I think the degree of respiratory symptoms they have really surprises them," she says. "A lot of them feel so sick they can't believe it's the flu." Nevertheless, she's pleased that fewer and fewer patients are demanding antibiotics. "I think more people understand that it's a viral illness." The time to see your doctor is if symptoms start to worsen after the illness should have peaked (about three days) or if you start coughing up a thick, green sputum.

6. There's nothing I can do to prevent the flu.

Wrong, on three counts. First, steer clear of people who have the bug. Second, wash your hands frequently. "It doesn't need to be super hot water you're not trying to sterilize your hands," says Skowronski, "you're just trying to wash the virus away." Nor do you need the fancy new anti-bacterial soaps. The soap isn't meant to kill the bug, its purpose is to make your hands slippery, so the virus slides off under water.

But how much hand-washing helps is still up in the air.

"There's some extrapolation there," explained Earl Brown, a professor of microbiology at the University of Ottawa. "I'm not aware of any study that's directly looked at the effect of handwashing on transmission of flu."

But it seems reasonable to assume handwashing probably plays a role since the hygiene measure is important for other respiratory viruses, Gardam said.

Third, and most important, get immunized.

"Immunization is a modern miracle," Skowronski says. The immunization does many things: it reduces the incidence of the flu, its severity, its duration and your level of infectiousness. Many people can get the shot for free (if you're elderly, a health-care worker or have a health condition) and a growing number of companies are offering them to their employees. Even if you have to pay for the shot yourself it's a bargain at about $10 at your doctor's office or local public health clinic. Still not convinced? Here are the numbers showing the vaccine's efficacy, from the Mayo Health Clinic in the United States:

  • 70 to 90 per cent prevention rate in healthy recipients.
  • 30 to 50 per cent prevention in elderly recipients.
  • 50 to 70 per cent reduction in total hospitalizations.
  • 50 to 85 per cent reduction in deaths.

The only reason to avoid the vaccine is if you're allergic to eggs (it's grown in an egg base).

7. I never get sick, I don't need a flu shot.

Trouble is, you may be sick and just not know it. About one in five people can have the virus and have no symptoms whatsoever. That means you may be unwittingly passing the bug along to your co-workers or, worse, your baby, your diabetic friend or your elderly grandmother. Dr. Alison McGeer, director of infection control at Toronto's Mount Sinai Hospital, says the day is coming when all of us will get flu shots. "I think that's where we're going," she says. Bottom line now: it's worth considering paying for the shot yourself, even if you're young and healthy.

8. The last time I had a flu shot, it gave me the flu.

Impossible. While the flu shot may give you a sore arm or make you feel a bit achy for a day or so, it can't actually give you the flu. That's because it's made from a dead form of the virus that "tricks" your body into thinking it's the flu, and jump starts your immune system into producing antibodies. "Some people may come down with the flu after getting the shot but that's either coincidence or they were already incubating it," Sourisseau says. It's also worth remembering that the flu shot is highly specific (it only protects you against the strains of the flu for which it was developed) and it won't protect you against the common cold.

9. If I get the flu, I can just take one of the new anti-flu drugs on the market.

Bonus points if you're aware that there are two new anti-viral drugs now licensed in Canada to fight the flu. They're known by the trade names Relenza, which is inhaled, and Tamiflu, which is taken orally. That's the good news. The bad news is that they have to be taken in the first 24 to 48 hours of illness when many people may not realize they have the flu. "The horse is out of the barn after that," says Skowronski. What's more, the drugs require a prescription. That fact has the potential for dramatically driving up health-care costs if people whisk themselves to the doctor at the first sign of a fever. Health officials have yet to come up with recommendations for the public on that question, Skowronski says.

10. Science will soon have the flu beat.

Well, not likely. The flu is a tricky virus; it mutates all the time, getting tougher and smarter. And every 10 to 40 years it mutates so radically, it leads to a pandemic. The most famous recent one, which occurred in 1918, killed somewhere between 30 million and 50 million people worldwide. There was another frightening bout in 1968. Scientists were worried that the avian flu, which claimed its first victim in May 1997, was going to be the next big pandemic. Before 1997, the virus usually caused only mild symptoms in humans, such as pink eye. So far, the virus hasn't shown that it can transmit itself very well. Outbreaks are usually localized and health officials have been acting quickly to contain outbreaks by ordering mass culls of bird populations when it does show up in flocks.