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domingo, maio 03, 2009

Escala 5 significa "the shit is about to hit the fan"


Tara C. Smith, a bonita professora de epidemiologia que escreve o blog Aetiology no Science Blogs, tenta explicar porque os céticos da gripe suína estão errados:


What does the WHO's pandemic scale mean? And why is anyone worried about this?

Category: General Epidemiology • Infectious disease • Influenza • Outbreak • Policy • Public health • Various viruses
Posted on: April 30, 2009 2:10 PM, by Tara C. Smith

I've been seeing a lot of comments mocking the current outbreak of H1N1, and a lot of people (and journalists) who don't understand what "big deal" is about the "snoutbreak" of swine influenza, or don't get what the raising of the World Health Organization's pandemic alert phase up to 5 means. I noted here what the alert level meant, but wanted to discuss it a bit more in a full post; after the jump.

So, some comments I've seen thrown about:

This is all just media hype! Lies about the Mexican cases! The WHO just revised their numbers down to 26 cases and 7 deaths! Why should I believe the crap about thisaporkalypse?

First, indeed, the Mexican cases stand at 26 cases and 7 deaths--*laboratory confirmed* cases. Even for regular influenza, the number of cases that are confirmed--much less to the level that these are, by the CDC or other high-level labs--is extremely small. We always expect many fewer confirmed cases than reported cases, because for a number of reasons, some people who display all the symptoms of a disease will be difficult to confirm. Maybe they were unable to get to a hospital in time for a sample to be taken; maybe they live in a remote area where it's difficult to ship samples from; maybe they came in too late after their disease had already cleared, and no live virus was present in their system anymore; and on and on. Most of the Mexican cases (the thousands reported) have been suggested to be H1N1 based on symptoms and timing. The current WHO report isn't saying that these 26 cases are the ONLY H1N1 cases in Mexico--these are just the ones they're absolutely, positively, 100% sure are swine flu.

Ordinary flu kills 36,000 Americans a year. Why should I care about this "swine flu," when only a hundred or so cases have been reported in the US?

Yes, ordinary flu is a bitch, and most people don't worry about it one iota. (Mike laments this situation). However, ordinary flu kills these 36,000 people *despite* many of us having some pre-existing immunity to the circulating strains, and a percentage of the high-risk groups receiving vaccination. With these new strains, it's unlikely that the population as a whole will have much cross-protective immunity, meaning higher numbers of people will get sick and die than a "regular" flu year, and all the impact to society and the economy that goes along with an ill population. As rhozack notes:

I live in a town with 65,000 people and somewhere around 300 hospital beds. If 20,000 people have the flu at the same time its like not having hospitals at all. Plus all the services those 20,000 people provide will be stopped at the same time and because of the nature of the thing, a large portion of your health care workers will be in that 20,000.

Now of course, we have no idea currently what kind of levels of illness or hospitalization H1N1 would cause if it becomes established in the population, but this is a situation where there's a small chance of a very bad situation, and so we need to prepare for it as best we can.

Does 7 deaths REALLY constitute a pandemic? Are we that wussy and panic-prone as a society that the WHO freaks out over a couple deaths from the freakin' flu?

And this is what I was getting at with my comment on pandemic phases. The number of deaths don't matter--it's the transmission in the human population that's key. Let's look attheir scale:

Phase 1-3 go from no animal viruses reported causing infections to humans up to the presence of a new animal or human-animal reassortant that's caused sporadic cases or small clusters of disease in people, but no sustained human-to-human transmission or community-level outbreaks.

Phase 4 signifies a new virus capable of causing community-level outbreaks. "Phase 4 indicates a significant increase in risk of a pandemic but does not necessarily mean that a pandemic is a forgone conclusion." This is where we were with the beginning of the outbreak in Mexico.

Phase 5 (and I'll quote directly from WHO here): characterized by human-to-human spread of the virus into at least two countries in one WHO region. While most countries will not be affected at this stage, the declaration of Phase 5 is a strong signal that a pandemic is imminent and that the time to finalize the organization, communication, and implementation of the planned mitigation measures is short. This is the key--Phase 5 is a signal to governments to get their act together, because the shit is about to hit the fan.

Phase 6, then, is the full-blown pandemic phase. This has not been declared yet. Maybe we won't get to this, the individual outbreaks will burn themselves out, and we'll head back down to a 4 or even 3. But for now, we're still seeing cases increase, and the prudent thing to do is be careful and prepared. Weren't any of these nay-sayers ever Boy Scouts?

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