Rapid onset of symptoms and Death

There was recently a discussion on the Rhizalabs Flutracker message board about the recent (as of mid-June) spate of rapid deaths in young, healthy people. I posted an explanation of why viral pneumonia from influenza seems to cause rapid onset of illness and death (often less than 24 hours) versus more "normal" bacterial pneumonia triggered deaths. This was apparently a well-received explanation as it was requested I repost it periodically. I am posting it here so I can have easy access to it. Note there may be some finer technical details that are off, but I believe this is largely good enough for the layman.

From various things I have read it seems the immune system treats a viral infection of the lungs much differently than it does a bacterial infection. Normally, your immune system has to fight off bacteria by having certain types of immune cells eat (phagocytose?) the organism. This can be done without the the extremely lethal parts of the immune system.

But a virus enters the cell and hijacks the internal mechanisms in order to make more virions. The body must kill parts of itself, either by triggering the infected cell to die (apoptosis?) or outright killing it. Whena virus infects the lungs the body has to mount an attack with essentially its full arsenal. This leads to a cascade that can result in, as I understand it, the spongy material of the lungs being transformed into scar tissue.

The progression is viral pneumonia -> cytokine storm -> ARDS -> (multiple organ failure?) The cytokine storm is a result of the viral pneumonia and ARDS and multiple organ failure are the consequences of the cytokine storm. This all happens very quickly.

Bacterial pneumonia takes advantage of the weakness in the body generated by the viral infection, and typically takes longer to develop. This is the cycle of being sick, getting better, then taking a turn for the worse.

Are we reliving 1918?

I am a member of FluTrackers where my name is wotan. Several weeks ago I started this thread:

I have been reading John Barry's The Great Influenza, and have been struck by a few things. First, I was aware that the first wave in the spring of 1918 was considered mild, but I did not realize the following:

The first wave (assuming it started in Haskell County, KS, which Barry says is more or less impossible to determine) appeared to be slightly more severe in the very beginning, but it was a slightly less severe variant that got out. Compare with Mexico, although I am not entirely convinced that the increased mortality in Mexico was due to anything more than not knowing to use Tamiflu in the early days of the outbreak.

Symptoms from the first wave were so light (apparently less than seasonal flu) that the disease could be mistaken for something else entirely. We have seen anecdotal evidence of swine flu being mistaken for any number of other conditions.

The first wave persisted in the northern hemisphere into August. Obviously, we are still in it here at the end of May.

There were isolated incidences of more severe disease during the first wave. There is at least some anecdotal evidence to support this in the current outbreak as well.

I'm still fairly early into the second wave in the book, so I don't know what else I will find.

Sadly, the parallels continue. Consider for a moment the demographics attacked by the 1918 Spanish Flu:

The unusually severe disease killed between 2 and 20% of those infected, as opposed to the more usual flu epidemic mortality rate of 0.1%.[9][12] Another unusual feature of this pandemic was that it mostly killed young adults, with 99% of pandemic influenza deaths occurring in people under 65, and more than half in young adults 20 to 40 years old.[23] This is unusual since influenza is normally most deadly to the very young (under age 2) and the very old (over age 70), and may have been due to partial protection caused by exposure to a previous Russian flu pandemic of 1889.[24]

Source: Wikipedia

Now, consider the demographics for the 2009 pandemic so far:

57% of the cases that we're having reported to us occur in people 5 to 24 years of age, and 41% of the hospitalizations are in that same age group -- the older children and young adults. But I also want to tell you about the rates, the cases per 100,000 population, and let you know that the highest rates of hospitalization are actually in children under 5. And the next highest rates are in those people 5 to 24. So it looks like this is a virus that's disproportionately affecting younger people but there are still lots of infections and hospitalizations in older persons.

Source: Flutracker's post of CDC transcript.


Let's make this clear. Seasonal flu disproportionately attacks the elderly. The 2009 pandemic flu attacks the young! The 1918 pandemic flu attacks the young!

Will the 2009 pandemic grow as severe as 1918? Probably not, but that it might is the scary thought.

Is this a Pandemic or not?

The short answer is yes.

The long answer requires an understanding of what a pandemic is.

From the Wikipedia article:

Definition

According to the World Health Organization (WHO), a pandemic can start when three conditions have been met:[1]

* Emergence of a disease new to a population.
* Agents infect humans, causing serious illness.
* Agents spread easily and sustainably among humans.

A disease or condition is not a pandemic merely because it is widespread or kills many people; it must also be infectious. For instance, cancer is responsible for many deaths but is not considered a pandemic, because the disease is not infectious or contagious.

This is a generic pandemic definition, and not specific to influenza.

For the case of an influenza pandemic we will add the following:

Influenza pandemics occur when a new strain of the influenza virus is transmitted to humans from another animal species. Species that are thought to be important in the emergence of new human strains are pigs, chickens and ducks. These novel strains are unaffected by any immunity people may have to older strains of human influenza and can therefore spread extremely rapidly and infect very large numbers of people. Influenza A viruses can occasionally be transmitted from wild birds to other species causing outbreaks in domestic poultry and may give rise to human influenza pandemics.

So, what are we dealing with? The novel influenzavirus A(H1N1) that is currently circulating is, by definition, a new virus in humans (though containing genetic material from previous human strains of influenzavirus type A), it definitely infects humans and can cause serious illness, and is capable of sustained spread between humans. Furthermore, it is a new virus from a different species (pigs). Therefore, despite the WHO's attempts at not declaring a full pandemic, the "classical" conditions are met.

It bears repeating, a pandemic does not have to be highly lethal, it has to infect humans in large portions of the world. The "Swine Flu" is doing just that, and the virus doesn't care what people say about it.

Why the concern

The novel strain of A/H1N1 influenza (swine flu) represents a potential threat to the health and lives of a large segment of the population worldwide. Although many are choosing now to discount this threat, it still remains despite the "mild" nature of the illnesses produced thusfar.

For those who want to look at the number of people officially listed as having become infected and those who died, here is what the World Health Organization says as of 5/11:

Influenza A(H1N1) - update 25

That translates out to around 1.13%. Seasonal influenza kills about 0.001% worldwide (citation needed). Granted, there are real problems with the numbers but out by the WHO, but for those who would point to that as evidence this is nothing bad, you have to look at what else the numbers say.

There is also the concern that the H1N1 and H5N1 (bird flu) viruses could meet in, perhaps, a pig or human, and the resulting virus could be highly transmissable like the novel H1N1 and with the high fatality rate of H5N1 (50-60% of persons infected with H5N1 die) (citation needed).

To be continued....

Diary of a Flu Year

This blog is meant to be a chronicle of what, in May 2009, looks to be the start of the first flu pandemic in 40 years.