# 3329
By now readers of this blog are no doubt aware that the figure bandied about of 36,000 flu-related deaths each year is an estimate.
No one counts the number of flu deaths each year, because most of the time, influenza isn’t listed as a cause of death.
Instead, we have a number of mathematical models that show a sharp rise in mortality, particularly among the elderly, during `flu season’. We also see a huge increase in hospitalizations due to P&I (Pneumonia and Influenza) during the winter.
Based on these, and other factors, statisticians have decided that somewhere between 30,000 and 40,000 American deaths are related to influenza each year, and about 200,000 hospitalizations.
Today, we are facing a pandemic of uncertain magnitude. And the question on everyone’s mind is:
Is this H1N1 `Swine’ flu any worse than seasonal flu?
The media has picked up the mantra `relatively mild’, while the WHO is describing the pandemic as `moderate’ – at least in developed nations at the moment.
Neither of which answers the question.
The problem is, our surveillance and reporting systems simply aren’t able to tell us about small differences in the severity of a flu virus.
At least, not this early in the game.
If this novel H1N1 were a stone cold killer, like the 1918 virus, we’d probably see that by now. Thankfully, that does not appear to be the case.
But what about a virus that is, say, twice as deadly as seasonal flu? Could we detect that this early in a pandemic?
Probably not.
If we use the CDC’s estimates for seasonal flu, we assume that about 1 person in 1,000 who contracts influenza will die as a direct – or indirect – result of the infection.
Many will develop pneumonia, secondary to influenza. Most will be elderly, or will have comorbid conditions that increase their risks of dying.
Most of their deaths will be attributed to cardiovascular disease, COPD, diabetes, or some other chronic condition – not influenza.
Quite frankly, when an elderly person dies, we often don’t look terribly hard at the reasons why. It was more-or-less expected.
There is, however, one cohort that we tend to watch very closely - and investigate- when we see unexpected deaths or severe illness.
Children.
Pediatric influenza mortality and hospitalization rates are something we watch closely, not only because of the tragedy that any child’s illness or death brings, but because they are more easily identified than elderly flu victims.
Seasonal influenza is generally blamed for the deaths of between 50 and 100 children in the United States each year. This CDC FluView chart was updated on May 30th, and so a number of recent pediatric deaths have not been added.
While the NVSN (New Vaccine Surveillance Network) has yet to show a rise in the hospitalization rate of infants and toddlers (0-4 years), the data reporting lags several weeks behind reality.
This is another metric to watch.
H1N1 viruses tend to affect younger people more severely than the H3N2 viruses anyway, but media reports suggest this novel virus may be having a larger-than-normal impact.
It is too soon, however, to draw any conclusions.
While an increase in pediatric mortality wouldn’t necessarily signify that we were seeing an across-the-board increase in the virulence of a virus, it would be a worrisome sign.
Pediatric mortality, followed by child hospitalization rates - of all of the influenza metrics used by the CDC - are probably the most accurate and the easiest to track.
And so, as unhappy as the prospect might be, we need to watch these metrics closely.
It is possible that this type of surveillance will be what gives us our first clue as to any changes in the virulence of this pandemic.
