Over at ScienceInsider (Science magazine's blog) Jon Cohen speculates about why swine flu seems to have spread faster and more widely in North America (Mexicon, US, Canada) than Europe and Asia. CDC thinks one reason is that by the time it was discovered here it had already spread widely. The Europeans, with advance warning, were then able to contain it with aggressive use of antivirals among travelers from the affected areas. I'm not ready to buy this.
This doesn't make sense to me, although nothing about flu viruses make sense, so I could be wrong about this. But it wouldn't explain why this fairly transmissible virus didn't spread outside of North America before it was discovered, assuming is true there was a lot of it around, possibly for months, before we detected it. Smothering the spark of a pandemic with antivirals was one of the hopes of many, including WHO. I was always skeptical, so maybe my skepticism about this is a reluctance to give up that position.
That said, I think it is premature to say what is happening or will happen outside of North America. It is common for flu to have a very patchy spatial distribution. Two cities in the same state can have very different flu experiences. The variation seems also to hold with pandemic strains. If you add to this the difficulty in diagnosing mild or inapparent disease, I wouldn't be too confident that Europe and Asia will be spared.
Still, this is an unprecedented situation. We are watching a potential pandemic evolve in real time, something we've never seen before. Thus it's hard to compare it to anything else.
We'll just have to work hard to collect the best information we can and look to see what it tells us.
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Differential propagation rates, differential surveillance data, differential national/agency actions, what have you.
Whether this thing is burning out or not (and thankfully it looks to be) various readings profferred over recent weeks would be easier to accept, whether correct or incorrect, if many in the public eye hadn't gone to such pains to make spectacles of themselves.
It has the appearance of organizational opportunism. It is disappointing and disgusting. It also masks the seriously important and dedicated work by those whose first (or second or third) thought isn't "Hey, look at me."
Might I suggest the economic and job environment in the US promotes the spread of illness. Specifically, people in the US are far more likely to go to work sick than people in Europe. You constantly hear tales of US workers unwilling to stay at home when sick because they'll lose their job, their car, their house or whatever. While in Europe, paid sick leave is readily available and not something you're likely to get fired over.
Glad to see you linking to ScienceInsider. Many thanks. This actually wasn't my speculation: It came from WHO and CDC officials. See also my interview with CDC's Nancy Cox posted today. She makes the argument in some detail.
Could the virus have ethnic preference? The hardest hit country in Europe was Spain. Mexico had the highest fatality rate, and North America has a large hispanic population. Would be interesting to see the ethnic breakdown of confirmed cases. SARS had an affinity for Asians, and Europeans have some genetic protection against HIV, so we know viruses discriminate.
It's hard for me to imagine that there's much genetic difference between Spanish and French for a virus to exploit.
If Mexico isn't just a reporting artifact (which I think is the more likely explanation) then I would expect it is the Native American component to their genome that would make any host-factor difference, since Native American are genetically derived from the Asian branch of humanity, which diverged from the African branch about 50,000 years ago. (I don't recall if Europeans diverged from Africans 30K or 20K years ago).
Of course, we've "watched" pandemics play out in 1957 and 1968 too -- we just didn't have the tracking tools we have now. Could there be an age thing going on? I seem to recall that most European countries have populations that skew a little older than ours. We already know that this H1N1 seems to spread more readily among younger people than over-50s. Maybe it's behavioral -- kids tend to be less hygienic, and a lot of young adults went to the hardest-hit areas during the recent spring break season -- but a lot of older folks from the U.S., Canada, and Europe travel in Mexico at this time of year too, and we don't seem to see lots of retirees getting sick.
Maybe people who have lived through several bouts of flu, fought off several more, and had > 20 flu shots covering many different strains over their lifetimes have a little more protection, and are less of a minority in different parts of the world than they are here.
Isn`t most of Europe still testing mostly the people who have traveled to Mexico or were in contact with someone who tested positively? IIRC the early European recommendations suggested people be on the lookout for severe symptoms and high fever which might not be as common among those affected as was though at the time of the advisory. Current CDC advise is to be on the lookout for a huge list of symptoms among, well anyone. So while European doctors might still be looking strictly for >38c fevers among stereotypical Latinos while the US might have moved on to testing pretty much all flue like symptoms.
I tried getting the WHO surveillance website to tell me how many test are done per country but the site has become less and less stable and things like this are best left for people who know what they are doing anyway.
I suspect the Americans are also testing like crazy since US media is about twelve notches more panicy than say European public broadcasters. This might mean a lot more people visiting a doctor with their flu.
The fact that Spain has 93 people who tested positive and Germany/France have 12, 13 would suggests that travel from Mexico really is a common theme, except it cant be since the US by now has found 3000 people who tested positive. I suspect air travel between the US and Europe/Asia surpasses travel between Mexico and the rest of the world. (have we seen the Japanese/hong kong "look at us probing and testing airplane loads of filthy foreigners for your safety" theater test Americans yet?)
The UK has 71 cases but 37 of those appear "in-country" which suggest wider testing which should be easy if you test in schools.
Sure the US is a big place for 3000 people but with cases in the big cities International travelers have a pretty decent chance of catching the virus. CDC has hundreds of cases in CA (LA?),NY maybe Chicago (Illinois and Wisconsin appear to have the most cases)
The CDC is bragging about how well it has distributed its new PCR test, I know European authorities were working on this and the WHO helps out with testing, but how vigorous are European authorities pushing tests?
Africa has zero cases and I doubt its because there has been so much antiviral treatment. Irin says thanks to the WHO there is some testing capacity but are doctor really sending in samples for testing? If I were a doctor in Africa the flu might not be my priority. Also there is trouble getting the agent needed for testing to Africa, something about "cold chain shipping problems" which I guess is a fancy way of saying lack of shipping freezers.
So is suspect the positive test figures reflect testing at least as much as the reflect infection.
Yes, it is puzzling why it has not yet effectively seeded.
But, I believe, without having seen the critical raw epi data, it shows the impact of 'behavioural control'. And that supporting my previous belief, containment may be possible - not through border control but through high quality surveillance in the community to identify cases early. Despite the limitations of current surveillance, it appears - though it seems to me too early to tell - that spread to Europe may indeed be stopped. But it will spread to Africa, unless spread is controlled in the Americas. And it may be possible to do so through the use of physical distance (>1m), especially for those who have symptoms and the other two key behaviours: hand hygiene and illness etiquette.
I think that a lot of what appears initially puzzling can probably be explained by three simple quantitative explanations, and hence testable:
1) denominator phenomena
2) environmental factors (temp. humidity, etc)
3) stochastic die-out with small numbers
I glanced a map of density of travellers by country to Mexico that pretty much matches the cases (Science Fergusson) , ie, cases refelect denominator differences, especially for Spain, where despite the continuing increase in cases, there has not been a corresponding increase in local transmision (??is that still so??)
With an Ro only just above 1 it does not take much to bring the actual R to under 1, especially if the environmental factors mean that Ro was higher in Mexico in Jan/Apr for this (presumably America) new flu virus than in Europe in spring. But perhaps Ro was same, as it appears to be less than 2, therefore only need to stop 50% of transmissions to make this virus die out. [Does Ro increase as the virus adapts?]
And we know that these two infections per each infected person are not in a Normal Distribution, with a skew for high numbers - super-spreaders for sociobiological reasons. So as long as the key person in the chain of spread is contained early. OK. If not, spread.
And, as stated above, I believe this is more to do with behaviour changes than antivirals. I wonder if putting infected people on tamiflu, especially if isolation facilities are sub-optimal may have a bigger impact of on flu virus transmission than putting contacts on treatment, as the contact will (sorry, SHOULD) get very early treatment in the event of illness onset.
UNICEF is working with WHO to define the priority behaviours to promote to update the 2006 advice on FluWISE that remains appropriate until the update is posted, expected next week.
Wash
Informed
Stay apart - outbreak setting, but good to practice now
Etiquette when sick: stay home, avoid others, cover coughs and sneezes
Dr Osman David Mansoor [] Public Health Physician
Senior Adviser EPI (New Vaccines) []United Nations Children's Fund [] 3 UN Plaza, New York, NY 10017
> I'm not ready to buy this.
but you don't say, why. What's your theory ?
> nothing about flu viruses make sense
you're not serious