Is this flu season bad? No one knows

Why there is no good measure of influenza virus infections, deaths, and similar respiratory illnesses


There has been plenty of discussion about a particularly bad influenza season in Canada, and even more so in the U.S., as both nations appear to brim with feverish, coughing patients. Things have been so bad south of the border that New York state and Boston declared public states of emergency and the U.S. Centers for Disease Control and Prevention (CDC) said that flu-related deaths have reached into epidemic territory.

But what does that actually mean? According to the CDC, the epidemic threshold for influenza—a virus that attacks your respiratory system, not your guts—is when related deaths account for more than 7.2 per cent of all deaths in a given week. For the week ending Jan. 12, 8.3 per cent of all deaths were due to pneumonia and influenza, just above the epidemic threshold.

This sounds scary, but the death counts from pneumonia and influenza actually aren’t all that high when compared to recent flu seasons. Check out the chart below:

U.S. Centers for Disease Control and Prevention

“So far the recorded (pneumonia and influenza) mortality is barely above what they call the ‘epidemic threshold,’” said Peter Doshi, a postdoctoral fellow at Johns Hopkins University School of Medicine who has studied influenza mortality, “but there is still time for things to change, of course.”

Though he said he doesn’t doubt hospitals are experiencing a surge this year, he asked: “What is influenza’s role in that? It’s not clear. It could be norovirus, coronavirus, respiratory syncytial virus (RSV), we don’t know.”

The patchy surveillance system for influenza

That’s because, the truth is, no one truly knows how many people actually have the influenza virus, how many people die from it, and how many others have illnesses that are masquerading as the flu. There’s no surveillance system for influenza anywhere in the world, no one tracks flu-related illnesses, and death estimates are mostly based on statistical models, not body counts.

The only way to know whether someone has influenza is to do a lab test. But flu reporting is based on people who happen to be tested since there’s no random sampling of the population. So if most people with influenza-like illnesses don’t go to the doctor or hospital,  they are never counted. This means that a lot of folks getting sick this winter may have influenza, or something else. As well, without random sampling, it’s hard to know what the baseline of sick people in a given year actually looked like.

As for flu deaths, Doshi explained, there are the confirmed cases, but statistical models try to account for people who die from a complication due to the influenza virus. For example, deaths from heart attacks brought on by sickness with influenza. But whether or not they actually had influenza is never confirmed. These are best guesses.

Another measure of the severity of the season is pediatric death from influenza. Doshi explained that when an elderly person dies, the cause of death is not always determined. However, pediatric deaths are more unusual and tests to confirm the cause of death in a child are common. As a result, this measurement tends to be more precise than the adult estimates. This year, U.S. pediatric deaths due to influenza are, thankfully, rather low. (So far, 29 this season.)  “Right now, for influenza-associated pediatric deaths, it’s the least deadly season since the CDC started recording (these deaths) in 2004/2005,” noted Doshi.

Here are the pediatric deaths for this year, as compared to other years:

U.S. Centers for Disease Control and Prevention

The flu situation in Canada

As for Canada, infectious disease expert Dr. Allison McGeer said that the consensus in the medical community is that it’s a busy season, and one that started earlier than usual, “but it’s not out of range.”

Here, too, Canada relies on imprecise statistical modelling to measure flu activity, and McGeer said it will take a year to gather enough data to know how bad the 2012-2013 season truly was. As for confirmed deaths nationally, the Canadian Press reported that there have been 15 in people 20 years of age and older, and no pediatric flu deaths. Still, in any given year, McGeer estimates, “There’s something in the order of five million flu infections in Canada, but we don’t test all those people.”

Why all the fuss about “flu-mageddon” this season?

“Some of this has to do with strategy around releasing vaccines,” said Doshi, “and some has to do with raising awareness to get people vaccinated. Different motivations are going into public health campaigns.”

There’s always an element of uncertainty that comes with the flu and there is no clear pattern from one season to the next. As McGeer put it: “If you’ve seen one influenza season, you’ve seen one influenza season.”

We can’t tell how bad it’s going to be, but McGeer did offer this: “About one in 10 years, we’ll get through a winter, and there’s almost no influenza. About three out of 10 winters, it’ll be a year like this year, busy. The other six will be somewhere in between.”

No matter the severity of influenza that year, public health officials suggest getting the flu vaccine. It doesn’t protect against flu-like illnesses but it does protect against influenza. The next best protection is something that’s almost free and doesn’t require a prescription: hand washing. Lots of it. Officials suggest aiming for five scrubs a day.

Science-ish is a joint project of Maclean’s, the Medical Post and the McMaster Health ForumJulia Belluz is the senior editor at the Medical Post. Got a tip? Seen something that’s Science-ish? Message her at julia.belluz@medicalpost.rogers.com or on Twitter @juliaoftoronto


Is this flu season bad? No one knows

  1. A scared public can be talked into anything, including snake oil vaccines for influenza. This is a heavily marketed scam to alarm a drama seeking public when in fact, the numbers of influenza are not out of average. stay scared sheeple and buy the vaccine! even though a single credible blinded, randomized controllled trial does not exist to prove efficacy.

    • “Stay scared sheeple and buy the vaccine!” I am not sure where you live but in Alberta where I live, the vaccine if FREE!
      Further, in the last three years I have known personally of three otherwise healthy people who died of influenza. Two of H1N1. They were 55 and 48 years of age respectively. One person died just this year and that person was 35 years old.
      As for the numbers of influenza suffers being higher this year, the hospital emergencies are over-flowing with sufferers who have been diagnosed with influenza. Francois Belanger who is an Alberta Emergency Medicine Physician came on television and told people NOT to come to hospital with influenza symptoms because they were overwhelming the ER’s. The articles in the newspaper are saying that ambulances in Alberta are seeing 15% increases in service calls DUE to influenza.
      The US is reporting the same thing.

      • The virus this year is H3N2 A or Hong Kong. Many people have had it since it was identified in the ’60’s and many are immune.

        • There is actually a new H2N2 circulating as well as a few other viruses that many people DO NOT have immunity to. As I stated, if the situation weren’t dire in Alberta, a head of ER medicine wouldn’t be on tv pleading with people not to come to the ER with symptoms of influenza. Obviously not everyone has immunity to this year’s flu.

          • “A few other viruses” do not the flu make. You may be right about H2N2. I’ve only heard that H3N2 A is the virus du jour. With our current mile wide and inches deep healthcare system, it doesn’t take much to overwhelm the ER areas. The WHO aren’t even reporting any flu’s.

          • You can look on the Health Canada site for Canadian information. Then you can go to maps of specific places to find out how widespread the influenza outbreak is. If you go to Calgary where I live, it is widespread. As well as in Edmonton. As for “a few other viruses”, there are A and B influenza viruses and they both cause influenza. Also, a cold doesn’t usually cause a headache (unless there is sinus involvement), muscle aches or weakness, extreme tiredness, chills and fever. Those are definitely signs of influenza. I can assure you as a nurse who has been in the business for 17 years, it is unprecedented during a normal flu season that an ER medicine head gets on the tv and tells people with the flu not to come to the ER. As for the immunity to the H3N2, it did have a big showing in the 60’s but that leaves out everyone who is 43 years old and under….they have no immunity and given that young children are most at risk for serious side effects such as dehydration, we have a whole lot of people who are risk…just not necessarily the usual suspects…the elderly.
            On a final note, the average Joe might not know the difference between a cold and the flu but an ER physician certainly does and that is what they are seeing in the ER. As for the WHO, I am not sure why they aren’t reporting it when every newspaper is.

  2. Julie, this is shoddy reporting. The ER physicians in Alberta are calling it an epidemic. The ambulances are overwhelmed. How do they know it due to the flu…because they have made diagnosis. Francois Belanger, a head of emergency medicine in Alberta came on the airwaves and told people with the flu to stay away from the ER’s. People are calling it an epidemic. Talk to some frontline workers…it is a bad year.

    • I do not want to question your professionalism or that of our doctors and medical care system and the much appreciated care you all provide in Calgary and Canada. I do question how the epidemiology is done to determine if it is truly influenza or influenza like illness, defined as “the flu” by the WHO organization. If you read a report from Dr. Tom Jefferson, a member of the Cochrane Collaboration (a not-for-profit international network of researchers, practitioners and consumers who prepare and update systematic reviews of the effects of healthcare interventions) you find that only about 7 to 15% is actually influenza as oppose to viruses like rhinovirus 16, metapneumovirus or others, with some hard to distinguish from influenza without specific tests. I won’t get into the flu shot vs not debate. You can draw your own conclusions from the science done on it. I don’t know if this site allows attaching links, so just google, Dr. Tom Jefferson influenzae reviewer cochrane collaboration, and you should find a pdf report done by him. Within this you will find further links to scientific studies.

  3. Good analysis, Julie. I had a very bad cold over Christmas which is still hanging around but it is not the flu. People don’t know the difference between the flu and a cold. The current flu virus this year is H3N2 A or the Hong Kong flu. This one has been around since the 1960’s and many people have already had it. Obviously people are no longer getting flu shots which is why the panic from the medical profession and their drug overlords this year. Just because a person shows up in ER with dangerous symptoms does not mean they have the flu, a bad common cold can cause the same issues.

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