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H1N1 (Swine Flu): Mild Pandemic? It All Depends On How You Define It…Don’t Lull Yourself To Sleep!

December 18, 2009

Mike Osterholm, CIDRAP Director and author of the subsription series CIDRAP Business Source brought up an important issue in this weeks writing…We should banish the word “mild” from the influenza lexicon. There’s no such thing as a mild case of influenza, any more than there are “mild” auto accidents or “slightly” pregnant. There are cases that for reasons we don’t understand don’t make you very sick, and there are cases that can lay you lower than you ever want to be, including the ultimate….death. What Osterholm does with great clarity is to revisit the idea this is a mild pandemic.

Both Osterholm and CDC’s most recent disclosure of about 10,000 deaths, 47 million infections and over 200,000 hospitalizations are thought-provoking once you really study the numbers. (http://www.cdc.gov/media/transcripts/2009/t091210.htm)

To compare the often quoted number of 36,000 excess deaths from seasonal flu to this 10,000 number is an "apples and oranges" affair. The 36,000 number is an excess mortality figure derived by different and non-comparable methods.

Here is Dr. Osterholm’s reasoning:

  • In that CDC study, only 9,000 of those estimated annual seasonal deaths are due directly to influenza or secondary bacterial pneumonia.
  • The other deaths are among persons who have influenza and who die of events like heart attacks or strokes.
    • If you want a comparison, think of the guy who has a heart attack while snow blowing his driveway after a large snowstorm and whose death is labeled “storm-related.”
  • More important, though it’s not just the number of deaths but the pattern of illness in the population, flu’s descriptive epidemiology:
    • More than 90% of the estimated seasonal influenza deaths occur in the elderly, who in many instances have existing serious health conditions that mean their deaths may not be far off, regardless of their influenza illness.

We all realize that death is inevitable and that “early deaths”—or those that occur well before our elderly years — ideally just shouldn’t happen. The way we count influenza mortality, an influenza-related death in an 87-year-old person with advanced Alzheimer disease is the same as the death of a 22-year-old otherwise perfectly healthy pregnant woman. Both deaths are equally tragic, but any reasonable person would agree they are not equivalent public health outcomes.

Of the estimated 9,820 deaths:

  • 1,090 (11%) have occurred in children 0-17 years of age
  • 7,450 (76%) in people 18-64 years of age
  • 1,280 (13%) in people over 65 years of age

This age distribution differs considerably from what we see with seasonal influenza.

While this pandemic is not 1918 (for which we can be most thankful - keep in mind no one knows what prevents this or any other pandemic from repeating that catastrophe), it is still pretty bad, already producing more estimated hospitalizations than seasonal flu and we aren't even into the heart of flu season yet.

  • It’s challenging our healthcare system unlike any previous seasonal influenza season over the past 30 years. That makes it hard for me to call this a “mild” pandemic.
  • Yes, there are mild, moderate, or severe influenza illnesses on an individual basis. But how do we describe a pandemic that hits a limited group of people really hard and causes only “routine influenza” for most others?

Most flu infections don’t have dire consequences (thankfully!), but a significant number do. And we never know who is going to win (or loose) the flu lottery. The convergence in our views extends to the same analogy: automobile accidents. As we’ve noted several times, it doesn’t make much sense to call any encounter with several tons of moving steel “mild.” It may be an encounter that produces little or no damage, but that’s luck. Anyone who’s gotten the repair bill for what can happen when hit by another car going only 5 miles per hour won’t consider the encounter “mild.” Any such encounter has the potential to be a catastrophe and the really bad ones are often just plain dumb luck.  And while the number of people killed each year in motor vehicle accidents is roughly the same as seasonal flu, we don’t usually think of our nation’s annual highway death toll of 40,000 as “mild” either. Its age distribution isn’t too different than pandemic flu’s either, the source of much anxiety to any parent whose child has just gotten their driver’s license.

It’s not just that “mild” is an inapt word. It is an inapt and dangerous idea. It is based on comparing total deaths in flu seasons with each another, not with the public health toll they exact. It is worse than a word not conveying the proper seriousness. It sends a message that itself has consequences, promoting a lack of urgency about taking rational public health measures like vaccination.

That’s especially pertinent this year when we don’t yet know what the usual flu season (January to March) will bring, either with seasonal flu or a recrudescence (“wave three”) of swine flu. As Osterholm points out, even with available vaccine now certain in the next few months, we are likely to find ourselves in January with a very large proportion of the population still without immune protection.

Are you feeling better that this is just a “mild pandemic?”

http://scienceblogs.com/effectmeasure/2009/12/mild_pandemic_bite_your_tongue.php

http://www.cidrap.umn.edu/cidrap/content/influenza/swineflu/index.html

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