The opportunistic flu virus

Those "sudden death" cases in otherwise healthy young people are probably the greatest mystery of all.

It is hard to imagine that such exceedingly severe courses really represent just the extreme end of a continuous clinical spectrum of a disease that is by its very nature self limiting and therefore non-fatal in 99.9% of all cases.

So I wonder if those cases represent a special, distinct cluster of the clinical spectrum, possibly related to some kind of very rare "allergic reaction" to the virus. In analogy to (for example) how
a very small fraction of the population may develop fatal allergic reactions to a bee sting (which, like influenza, is painful but harmless for most people).

Now the big question would be to find out which factors exactly contribute to this vulnerability
of otherwise healthy people.
"influenza virus allergy"(*) or predisposition for a "cytokine storm" or special anatomic features of the respiratory tract or ... ?

Once this risk factor(s) are identified, lifes could be saved with the proper pre-cautions targeted especially at the vulnerable persons (e.g. self-quarantine, prioritized vaccination, prohylaktic antiviral treatment...)

P.S.: This "allergy" theory would also explain the fact that pandemic viruses seem to lose their deadly impact in the younger population in subsequent influenza seasons which would be simply due to the fact that those who are genetically susceptible to the "virus allergy" have already died throughout the first waves of the new virus.

So, not only does the virus adapt to the human population, but the human population in turn adapts to the virus in a co-evolutionary sense ....

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(*) I use the term "allergy" just as a metaphor here, for lack of actual knowledge of the real phenomenon.

P.S.:
Are there any studies to date that specifically address the subset of fatal cases in the 'otherwise healthy' category in order to help clarify the question wheather those just represent the extreme tail of a continuous spectrum of clinical desease (unlikely?) or if there are hidden (yet unknown) risk factors that have not been identified yet ..

Should women postpone pregnancy plans until the pandemic has passed? Even if postponement carries its own risks for age reasons? If and when the vaccination is ready, would planning a pregnancy be enough to put someone into a "high-risk" group for availability?

Sorcha: I am reluctant to give advice of this kind. If it were my daughter, I'd say, "Live your life as you would have without swine flu, but be prudent in the way you do it." Most pregnant women have no problem, flu or no flu. Some have bad luck even without flu (as my daughter found out with her first pregnancy; things worked out after that, I'm happy to say). Ask you doctor his/her opinion and then make up your own mind.

H1N1_watcher: The (excellent) question you are raising is the shape of the probability distribution for severity (e.g., is it multimodal and not, say, bell shaped). We don't know that. However there are crude estimates about the proportion of cases in the upper tails that can be made regardless of the shape (e.g., use Markov's or Chebyshev's inequality) and some proportion will be in that upper tail, we can perhaps say that much, and given that, I think the post is still valid.

As the labs are now too busy to test every suspected case of swine flu, wouldn't it make more sense for them to switch to completely random testing of the population in order to work out what percentage of people in each part of the country / world have the virus? I've seen people suggest here that many who have the virus may be completely unaware of it, so the figures for the number of cases could be miles out.

Apart from pregnancy as a risk factor with this flu, prospective parents may also want to consider the state the health care system could be in if/when the flu hits hard during regular flu season. But with a vaccine available later this year the tail end of the next northern hemisphere flu season may not be too terrible.

Robert: That's essentially what national flu surveillance systems do, taking specimens from a population-based set of hospital labs. It makes sense from all points of view.

Individuals differ in the way they react to viruses. A virus that binds deep in the lung can trigger potentially fatal pneumonia if the person infected mounts a strong inflammation in response to it..

The last H1N1 pandemic in 1918 was notorious for causing such rapid, viral pneumonia, which can kill within hours. "The binding and replication of the pandemic H1N1 virus in the lower respiratory tract in ferrets is consistent with the viral pneumonia that is observed in humans," Fouchier told New Scientist.

The Dutch group has found that swine flu binds deeper in the respiratory tract than seasonal flu.

They theorize that it can cause viral pneumonia, followed by an immune overreaction, lung inflammation, and then death to explain the lethal attacks on young, healthy people. Whether this is actually the case and whether it is the fabled "cytokine storm" isn't too clear right now. Really need some clinical case studies on this.

While younger people are at risk, don't forget the older people. IIRC, the average age in fatal cases was 37. Looking over the risk factors in the table, I would estimate that half the boomers have at least one. Arthritis?? Who over 50 doesn't have a touch of arthritis in one place or another?

One of my friends has 4 of those risk factors, although none are severe and all are well controlled. Going to be a long winter for a lot of Americans.

raven: The MIT group, however, found it bound with less affinity than seasonal flu. Grabbing on to the latest findings in a rapidly evolving literature can be hazardous. The MIT group has a different take on receptor binding than the conventional view (i.e., it isn't just alpha 2,3 or alpha 2,6 that is critical but the nature of the alpha2,6 or 2,3 configurations). We posted on it here. What does this all mean? I'm not sure. We are learning a lot of interesting stuff, but applying it is difficult at this point. Maybe soon. But not, IMO, now.

3 more UK deaths reported today... all of whom had "underlying health problems".

What I am don't understand.. and forgive me if it is a bit fundamental... is what these folk are actually dying of ? At one level yes it is swine flu... but surely in a modern ICU, a patient that is intubated with good Oxygen supply access to state of the art antibiotics, blood filtration etc should pull through ?

I wonder if the high number of sudden deaths noticed might not be more to do with not detecting deaths that take longer as by then the virus is no longer in peoples systems it cannot be detected and therefore doesn't fit strict WHO reporting requirements.

I wonder, too, if it matters if these conditions are under good control. Many people just use albuterol to control their occasional asthma symptoms, not treating the underlying inflammation. Is this a factor in these deaths? I'm sure we'll never know.

The asthmatics I know, myself included, are all wondering what's smarter right now: Stay on controller meds, which might reduce immune function but also reduces inflammation. Or reduce medications like Singulair and inhaled corticosteroids to improve immune function.

Me, I'm staying on my meds (inhaled corticosteroids and Singulair) until told to do differently. Like you said, live your life like you would flu or not, but be prudent.

Why do the media not report what exactly these "underlying health conditions" are? I presume they don't want to induce panic, but as the parent of a 3yr old type 1 diabetic, I'm already panicking!

I'd like to know if any of the child deaths involved diabetics, or are they talking about other conditions such as asthma, or more serious things like cancer?

I know there really is no point in worrying, but I'd hate to think I was worrying unneccessarily!

According to the CDC many of the severe cases were obese.
http://ow.ly/g52o

The common thread to the chronic conditions a/k/a pre-existing conditions, seems to be chronic inflammation due to metabolic syndrome...(obesity,diabetes, heart disease etc.) Metabolic syndrome has shown to impair lung function http://www.nature.com/oby/journal/v14/n9/full/oby2006190a.html

There is also some evidence that asthma is a related syndrome
http://www.medicalnewstoday.com/articles/24118.php

What causes metabolic syndrome? A complex cascade of hormonal reactions to repeated surges of insulin. The surges are caused by diet high in carbohydrates.

I just wonder if diet is the ultimate risk factor.

I got totally flamed on another site by suggesting this idea. I just want to explore the concept...and just know that I am not judging or condemning anyone.

Worried, I am not a doctor, but I believe different metabolic conditions are present in type 1 than the metabolic syndrome type 2 (which I am specifically addressing). I am sure you have made yourself an expert in the field and can school us all! I am a mom of a 5 year old who has challenges, so I totally understand your "name".

Any insights into pts with immunological disorders? RA, Lupus etc, and those on immunocompromising treatments, whether agents for HIV, RA, Chemo? Anything in general with overacting or compromised immune systems?

FYI-Revere... New strain recombination/reassortment in Saskatchewan. Two humans, possibly three. Two recovered. Pig farmers. H3N2 with H1N1 as a new bug. Novel? Dont know but its certainly no Rimouski.

Should be on the wires within hours.

Randy: Was on the wires hours ago. Sounded like it was H1N1 seasonal with classical swine flu innards but might have been H3. We'll hear the details soon enough.

Curious:

I've wondered about that, too. Though ending up at the ER with an asthma attack because you went off your cortisone inhaler seems like it would add quite a bit to your risk of catching the flu, as well as the risks of some kind of massive asthma attack. (And then, the doctor puts you on five days of prednisone pills, which I think has a much bigger effect on your immune system.)

Revere, any news on how gnarly it is? They were fully recovered 8 days ago but it didnt sound like a happy recovery. Sounded to me like a really, really bad case of H1N1 in Mexico. Efforted the nationality but nothing there yet.

I got this four days ago but folks in Toronto werent sure because of the sequencing stuff what they had. Seems that the infection was almost 3 weeks ago, then the recovery. I thought that this was yet another case of H1N1 but it was displaying some sort of nutty symptoms.. 101 F, malaise, conjunctivitis, muscle aches and pains, pounding headache and then a slip to no fever, but all the symptoms for two weeks.

Interesting.

They were amazed of course but hey who isnt nowadays by this stuff?

So now they HAVE to TEST rather than sample do you think?

Asthma is a risk factor for dying from this flu. What does that mean? My husband and i both have asthma. I have used my inhaler twice in the past 3 years (once three years ago when i got a bad cold while pregnant and this past year, again, bad cold while pregnant, used it once). My asthma is basically nonexistent unless i am pregnant and have a cold. My husband used to have chronic asthma, he used to use inhalers and steroids all the time to control it, but hasn't had to use anything in over six years. Not sure why. So are we at risk? I just read that two preemies in a MIAMI nicu fought off very mild cases of this flu. I have a 30 weeker, home now after almost 2 months in the NICU. I have been freaked out about her catching this flu--now maybe i don't need to worry about her so much.? I hope. Just wish we could figure out who else needs to be really worried and take extra precautions, not just the general precautions. Who needs to really hibernate this fall/winter instead of just washing their hands all the time and avoiding coughing people?

Randy: You describe a typical case of flu. There are probably many odd reassortments out there that don't propagate and this may be one of them. We'll find out. But they can't test all ILI. Not feasible nor productive.

Lulu: If you look at people with flu complications, there is a higher proportion of people who have a history of asthma amongst them than in the general population. That's what it means for asthma to be a risk factor. But as you point out, that might not be very informative for an individual. How bad does your asthma have to be? How complicated does it make the flu? Etc., etc. So it is a general statement about a population of flu infected but may not be very informative for an individual. At some point we'll probably know more about this, but not now. That's why supporting science is a good investment.

Thanks for the info. I'm married to an environmental scientist who comes form a very sciency family--a phd chemist and and physicist among his brothers. We try to support science as much as we can. THis is a great site, by the way.

Weeks ago, someone posted to the effect that a nasty flu laid Vermonters low in February, and could it have been H1N1, or a close relative. Same event in Maine, and state CDC attributed much of that February flu then to type A. Seeing as how H1N1 is type A (speaking obviously as a lay person and just testing a thought, seeing as how many in Maine, including myself, were laid out for weeks, literally, with all the symptoms of H1N1 (upper respiratory, fatigue, headache, fever chills, intense sore throat, earache) the likes of which none of us have seen in years -- is it possible that some in the population have already met this particular virus?

Not to mention that more deaths of younger (60s, 50s, even teens) attributed to the flu were popping up last winter (anecdotal at best, but from one who keeps an eye on media around the world)

downeast: Yes it's possible/em>. More likely it was seasonal flu, which made up most of the flu in February. Some of it was H1N1, some H3N2 (usually a little more severe) and some of it was probably flu B, which was around quite a bit at that time. Swine flu clinically is a lot like seasonal flu, so we can't tell them apart on the basis of the symptoms. They look different epidemiologically, with an age shift to the left for swine flu, but we'd have to know the age distribution in Maine and VT to make that case and we don't. Bottom line: possible, yes. Some cases might have been. But probably not most of them.

Thanks. Not to belabor the point, but will throw out one more anecdote.

One student in a small town was diagnosed with swine flu (state CDC-tested). According to school nurse, the student had attended school sick, went home, returned to school with symptoms, and so was there with other children at probably most contagious point in illness. Yet, no other student fell sick (again, school said). Because they had already met this bug three months ago? Can't imagine it was due to exceptional hygiene practices among young teens.

Understand completely now the need for more influenza research funding. Thanks again for your insight.

This H1N1 flu has really got me on my toes. I have been living with Lupus for 32 years and it is hitting my lungs. I spent some time in the hospital this year because of my breathing. I have just spent the last year off work and was really hopping to return in September. Unfortunately for me I am a teacher and lets face it, kids don't stay home when they are sick. I would really like to know what the risk is for people with lupus because there seems to be a lot of confusion out there as to who is at risk.