Wednesday, June 10, 2009

Measuring The Severity Of A Pandemic

 

# 3318

 

 

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It was six men of Indostan
To learning much inclined,
Who went to see the Elephant
(Though all of them were blind),
That each by observation
Might satisfy his mind
"The Blind Men and the Elephant"
by John Godfrey Saxe (1816-1887)

 

This story has been attributed to the Sufis, Jainists, Buddhists or Hindus and has been used by all of them to teach that a limited perspective can lead scholars, teachers, and clerics to the wrong conclusion.


In this story each blind man touches a different part of the elephant, and each comes away with a different opinion of what it must be.

 

In the Buddhist version, each person decides the elephant must be like  a pot (the elephants' head), wicket basket (ear), ploughshare (tusk), plough (trunk), granary (body), pillar (foot), mortar (back), pestle (tail) or brush (tip of the tail)

 

And so it is with our global (and even national) influenza pandemic surveillance systems.  

 

We see only bits and pieces of the entire picture, and must try to figure out what the entire elephant (or in this case, a pandemic)  looks like based on incomplete information.

 

If someone has the H1N1 virus, and dies, but was never tested . . . are they a pandemic fatality?

 

Right now, the answer is `no’.  Not officially

 

A great deal has been made about the low number of deaths attributed to the H1N1 virus.  `141 deaths’ has been bandied about over the past couple of days, particularly by pundits looking to disparage any pandemic declaration.

 

I doubt, however, you can find any public health official that will proclaim a lot of confidence in that number.  

 

Each day, in the US alone, about 6,500 people die.

 

Globally?  It’s probably closer to 160,000 deaths.    How many of these, do you suppose, are checked to see if influenza was a contributing factor?

 

The answer is: not many.

 

Of course, by far and away, the vast majority of these deaths are unrelated to the H1N1 virus.   We `know’ that, even though we are unable to quantify – with precision – the number of deaths actually due to the virus.

 

The `141 deaths’ worldwide represents some unknown percentage of the true number of deaths.  Just as the 27,737 confirmed cases (as reported in the WHO update #46) represent some percentage of the number of actual H1N1 cases.

 

No one really knows the size of this elephant, since we are only privy to select pieces.

 

It is unlikely that this virus is much more virulent than seasonal flu, else we’d probably have seen some spikes in the 122 MRS (122 Cities Mortality Reporting System).  

 

These numbers do, however, tend to lag several weeks behind reality. So we will continue to watch them.

 

If, as suggested by CDC officials, the real number of infections in the US is 20 times higher than 13,217 currently reported, then we must be closing in on 300,000 cases nationwide.  

 

And that, admittedly, may be low.

 

The virulence of this virus has been compared to that of seasonal flu, with some estimates putting it a bit higher.   Seasonal flu, it is believed, kills about 1 person out of every 1,000 that it infects.  

 

If this virus is comparable, we should have seen 300 deaths in the United States so far, not fewer than 40.

 

But that assumes we can detect and report all of the deaths.  And we can’t.   We don’t do it for seasonal influenza, and it is unrealistic to expect we can do it for H1N1.

 

Over the past month, since this virus began to seriously spread across the nation, we’ve had nearly 200,000 deaths from all causes. 

 

It would not be difficult for 260 deaths (or more) to be simply lost in the background clutter.

 

After all, most deaths do not result in autopsies, and fewer still are ever checked to see if influenza was a factor. 

 

When someone dies from something other than trauma (or misadventure), a chronic illness is almost always cited by the attending physician as the primary cause of death.  

 

Cardiovascular disease, diabetes, COPD  . . .  If influenza contributed in any way, it is rarely listed on the death certificate.

 

The deaths we are hearing about attributed to the H1N1 virus are primarily those that occurred among people being treated for the flu in the hospital when they died.

 

And in many countries around the world, where medical care is marginal and surveillance is lacking, we probably don’t even hear about those cases.

 

None of this is to suggest that somehow we are failing to recognize a highly virulent virus.  

 

While surveillance may not be perfect (and in some places it is practically non-existent), I believe we’d have picked up on any excessively high mortality rates by now.

 

The point is, the numbers we see are clearly just part of the elephant.   I believe that the CDC and the WHO are already factoring in what they know they can’t see.

 

 

I also suspect they are probably pretty close to right when they call this virus `mild-to-moderate’ in severity.   

 

 

That could change of course, and will likely vary depending on what populations are being affected.   Some regions of the world may see a much worse pandemic than others.

 

For now, it is too early to place much faith in the partial numbers we are getting.  As the southern hemisphere gets deeper into their flu season, we may begin to get a better idea of this flu’s impact.

 

Until then, about all we can do is accept that we aren’t seeing the whole elephant, and plan accordingly.