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Sunday, May 17, 2009

Swine Flu Goes Pandemic

Update: Japan up to 120 odd cases, expects case count to reach at least 130. One bank employee has tested positive in Hyogo and in that branch all non-essential employees will be asked to work from home for a bit. 39 Osaka reported cases. Most of the cases confirmed so far are in Kobe. The likely candidates here for transmission vehicle into the country are ships. Anyone want to give a guess how long until this explodes in the floating ships-at-large fleet outside Singapore? From there, all of Asia. Also, the Netherlands reported a PB2 gene change in one case a few days ago. From what I've read, the current PB2 is avian, which may account for the warm-weather spread. End update.

That's pretty much it. Japan is up to 78 cases and thinks it will be reporting quite a few more. So that's the official stage six - community level in more than one region. The new pandemic stages were released in draft form last year.

People are currently underestimating this. In the Americas, where this has been running for a few months, the flu continues to spread at a time when normally flu activity is dropping quickly. The Japanese wave, currently detected in multiple high schools in multiple towns, is another counter-trend breakout.

The recent concern and attention had shifted to the southern hemisphere, which is heading toward their peak flu system. To have another emergence in the northern hemisphere at this time raises the stakes.

In "bad" flu seasons, the US can see 10,000 - 15,000 more deaths than normal. In pandemics, one could easily see 50,000 or more extra deaths even if the virus is not particularly lethal because of the higher penetration rate in the general population. If an extra 10-15% of the population gets the virus, that's an extra 30 million or so cases. The US is currently up to 5 deaths and the CDC estimates that half the flu cases in the US currently are swine flu. The US is seeing an unusual rate of flu at this time of the year, but quite a bit of it seems to be due to crappy weather. Global cooling strikes again. However, over half of subtyped A virus samples in week 18 were swine flu.

In terms of economics, it looks like swine flu will be a drag through 09/10. I think it is going to be much more of a problem for the emerging countries, but it may knock as much as a quarter of a percentage point off US GDP over next winter. That's assuming, of course, that the virus stays in its current form and that nothing nastier emerges. The virus appears to be pretty fixed right now, but one never knows. Even having one of these out there circulating in tandem with the normal flu strains greatly raises the probability of multiple crossovers, the regular flu shot becoming less effective, and more probability for individuals of getting sick from flu twice in one season.

Currently swine flu is a risk to pregnant women, probably young children, and anyone with health vulnerabilities.

I don't believe for one moment that this new swine flu just emerged a few months ago. It's too fixed and adapted.

So it's time for US citizens and businesses to ramp up on the old preparation thingie. There's nothing here to get hysterical about, but parents need to think how they'll handle daycare issues, especially in light of the high probability of a lot of schools closing next year, and businesses need to figure out manpower issues that may cause them problems. Individuals with higher risks need to contemplate their own personal risk control measures.

Comments:
The CDC has been saying for a while that these pandemic levels are really a signal from WHO to various countries--because the virus is already circulating freely int he US, we're already well into the situation.

There was an article in the Post today on this, very interesting about how pandemic flu strains disproportionately affect young, healthy people compared to seasonal flu.

http://www.washingtonpost.com/wp-dyn/content/article/2009/05/16/AR2009051601850.html

"In the 1918 pandemic, which killed at least 50 million people, nearly half the deaths were of people 20 to 40 years old. More than 95 percent were of people younger than 65. In comparison, 36 percent of the deaths in the 1957 pandemic were of people younger than 65, and 48 percent in the 1968 pandemic. "
 
Joy - again, one of the reasons for that is the fact that pandemic viruses are novel, and the population has not had a chance to build up an immunity.

Older people have generally been exposed to a wider range of viruses and will have more resistance.

You cannot compare the 1918 epidemic to this one, because that was in the pre-antibiotic era when urbanized people were exposed to very bad air quality, and when bacterial infections abounded. TB, for example, was endemic.

Most of the deaths from flu in 1918, based on descriptions, may have been from other infections. The flu often allows very mild bacterial infections to suddenly explode even now. But now we have excellent supportive treatments and antibiotics for most bacterial infections. That cuts our death rates sharply. In countries in which poverty, poor water qualify, poor nutrition and high levels of other disease in the population are still problems, much higher death rates from severe viral infections are still seen.

We probably have had at least 70-80K infections in this country. So far we only have 5 known deaths.
 
It is true that we have much better treatment options for bacterial superinfections (the usual cause of death in typical flu seasons) but there is also some evidence that the disproportionate death rates among young, healthy victims of the 1918 flu were caused by the flu setting off a "cytokine storm" for which we still do not have adequate treatments (though the ACE inb hibitors and ARBs may be helpful.) It would be best if we develop a decent vaccine post-haste. I don't think we have heard the last from swine flu; the next few months will be telling.
 
1918 appeared to be the worst flu ever in the history of the world, so I would not compare this one to that. However, the 1968 and 1957 age-mortality distributions were interesting and are probably more comparable to what we're seeing now. All of the deaths in the US from swine flu so far have been to people under age 65.
 
Joy - I phrased that badly. The 1918 flu was very similar to this one. It was an H1N1 with a swine/avian/human mix.

Whether it was the worst in history we don't know, because there appear to have been about 3 flu pandemics a century in the 1700s, the 1800s, and the 1900s. Plagues have been a feature of human history for a very long time, and the combination of pigs and fowl exposure appears to have been a risk factor for thousands of years.

What I really meant to say is that a virus of similar lethality to the 1918 virus wouldn't do the same thing now that it did then because of the change in medical tech.

The age distribution may purely be a factor of immunity in older folks - call it the geezer advantage.

I wish I had kept the link, but a few years ago I ran across a very interesting study done on 1918 antigens, which seemed to show that many people had been exposed to the virus and had thrown it off without ever even knowing they were ill. That virus might have been very similar to this one.
 
SW - it is an interesting question.

I have read a great deal about the cytokine storm theory. I am dubious, because although inflammation of the lungs appears to be a factor in many virally-caused deaths, we don't seem to see much evidence that flu is specially apt at causing this. The accounts from physicians that I read seemed to described rapid spread and death among stressed young populations, plus secondary bacterial infections among less stressed populations.

The early deaths in military camps would be consistent with low general immunity levels rather than a disproportionate immune response. And is anyone who is familiar with the grind of a typical Japanese high school surprised that the disease is breaking out in that population? The average Japanese high school student is quite sleep-deprived!

Of course, if this virus acquired the long connecting chain that H5N1 has, all bets would be off. But a virus as lethal as H5N1 would tend to be self-limiting.

If this gets into the Palestinian population, I bet you will see a staggering death rate from fungal and bacterial co-infections.
 
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