Thursday, April 30, 2009

If it's a "mild" flu isn't that better? Well, isn't it?

Some food for thought.

By Leva Cygnet

I've been seeing comments around the blogosphere to the effect of "it's a mild flu" and "only 150 out of a population of 110,000,000" are dead in Mexico. I thought I'd do some analysis on the reported swine flu numbers regarding what they might be showing, and what you can infer from them.

First off, Mexico is reporting that there are 157 suspected fatalities and 7 confimed. For ease of argument, I'm going to round this down 150. And yes, I know it's likely some of those suspected fatalities died of other things, and equally likely that Mexico is so disorganized and overwhelmed that they're under-reporting matters. I'm going to take the number of "150" and stick with it for this article for math purposes. You can do the same math yourself on any number you chose to play with.

We cannot calculate a case fatality ratio (CFR) from those 150 dead because we don't know how many are sick. Lots of people are, or have been, hospitalized but it's highly probable that many more people are recovering at home. Swine influenza seems to be behaving exactly like one would expect a new influenza to act, and it is not Ebola or Captain Tripps the Death Flu. This means most people will recover just fine in a few weeks on their own and no doctors need be involved.

What we can do is apply various CFRs to the number of dead to figure out how many people might be sick.

Here's some examples:

The 1918 pandemic had a CFR of around 2.5%. (Though this seemed to be highly dependent on personal genetic resistance and the capriciousness of viral mutation; it would make some people mildly ill and, elsewhere, wiped out entire communities.)

Taking a CFR of 2.5% gives us 150 dead and 6,000 total infected.

That, alone, is unstoppable. 6,000 people are way beyond the ability of any city to manage, even one as big as Mexico City. To stop the flu at that point you'd need to identify every single one of those 6,000 people, put them in isolation, and -- assuming no one was infected with a mutated Tamiflu resistant version of the flu -- shove Tamiflu down the throat of anyone who'd been in the same breathing space as the sick person during the period they were potentially infectious.

Flu is infectious for 24 hours before symptoms to as long as 7 days after. If even one of those people took a crowded subway, went to a sports game, or went to a busy night club, during a period that they were infectious ... well. Game's up. Flu is entirely contagious enough to have added scores of new victims just from one subway trip. It's airborne.

At just 6,000 sick people, my logic tells me the flu would be nigh unstoppable.

If the CFR was lower -- if the disease is less lethal -- there will be more sick, of course. A CFR of .5% gives us 30,000 sick. A CFR of .1% gives us 150,000 sick.

Note that a lower CFR is not necessarily a good thing. The way I see it, either we have a disease with a relatively high mortality rate that is spreading and probably unstoppable in the human population, or we have something that doesn't kill very many people, but is so contagious that it's infected tens or hundreds of thousands of people in several weeks. Either isn't a very good scenario.

The second scenario, a wickedly infectious flu that doesn't kill a lot of people, is problematic on several fronts. One, it will kill some, as demonstrated by the numbers coming out of Mexico. And it would really suck to be one of those people, or their friends or family.

If you take a city the size of, say, the Phoenix metro area (two million) and half are infected and .5% die, that's still 5,000 people dead. For the entire US, with roughly 304 million, if half are infected and .5% die, that is 760,000 people. Worldwide, assuming eight billion people, twenty million could die. Odds are, however, that influenza's going to tear through the Third World with a lot more savagery than it hits modern nations, so the global CFR may be worse than what we're seeing now. Mexico may have a lot of poor, but it's nothing like Congo or Somalia or Haiti.

Secondly, aside from the dead, there will be many people who are sick enough to need medical care. If a "mild" but extremely contagious flu strikes, the number of ill could overwhelm the hospitals. Even a mild flu can be devastating to someone with preexisting health problems, or who is young, healthy, and unlucky enough to have an immune system that goes into overdrive. (We're already seeing this in Mexico city -- they have armed guards at the doors of public hospitals who are turning patients away.) There could be shortages of medication, supplies, and hospital beds.

Some quick calculations, using Phoenix for an example: Two million people. 10% sick at the same time gives you 200,000 sick. If just 5% need hospitalization that is 10,000 people. (How many of those 10,000 will die if they don't get the hospital care they need?)

This affects not just flu patients, but everyone for falls ill or is injured for any reason. If all the ventilators are being used and you're in an auto accident and have a chest injury and need one, you're up a creek. You'll die. The equipment wouldn't be available to save you. Plus, anyone who goes into a hospital would potentially be exposed. It would really suck to develop, say, have a treatable heart attack and then die of influenza complicated by your heart disease.

Thirdly, "mild" flu is only mild until you're the one who's sick. Flu is miserable. A mild, uncomplicated case of influenza will knock you flat for a week and, while it might not kill you, it will make you wish you were dead. If tens or hundreds of thousands of people are sick in a city, it can bring normal life in the city to a screeching halt and disrupt things in spectacular ways. (Mexico City is currently experiencing runs on grocery stores. People are panicking and they are literally running out of food.)

Finally, flu viruses have the capability of swapping genetic material with other strains. That's how swine flu was lborn -- likely, a pig was simultaneously infected with avian, swine, and human viruses. The viruses had virus sex and swapped some genetic material and their nasty little lovechild was born. Then some unlucky person caught that new flu virus, and an epidemic began.

During a pandemic, with lots of people sick, we can assume there will be lots of particles of swine flu virus floating around out there. However, seasonal flu isn't going to go away, and seasonal flu and swine flu could swap genetic code and then swine flu could learn some nasty new tricks, like Tamiflu resistance or increased virulence. It could also meet up with something really unpleasant, like avian H5N1 flu, which isn't really adapted well to humans (yet), but which has some genetic code that kills about 60% to 70% of people who are so unfortunate as to catch it from birds.

We really don't want any human-adapted flu to reassort with H5N1. The same thing that happened with the afore-mentioned pig could happen with H5N1 and if H5N1 retained its lethal nature That Would Be Bad.

On the other hand, if the CFR is higher, 150 dead gives us fewer patients. It's not spreading as fast. However, you can calculate the rate of spread of a virus by how many people each person, on average, infects. If each person infects greater than an average of one other person, the outbreak is growing and has pandemic potential. (AIDs, for example, has a very low rate of spread but it's definitely not dying out -- the rate of spread is greater than "1".)

A slow rate of growth, despite a higher CFR, may make swine flu more manageable. It would be easier to implement social controls such as quarantines of the infected, closing public places, and discouraging travel, to reduce the rate of growth even further. Slow the spread enough, and the hospitals don't become overwhelmed. While getting the rate of spread below "1" would be unlikely, it might be possible to keep it from growing in exponential leaps and bounds. Eventually, a vaccine will be created, and we can bring the pandemic to a standstill -- at least in those areas of the world where a vaccination is possible. (The toll that pandemic flu will take on certain third world countries will be appalling.)

However, slowing down the spread of the flu will require communities to accept restrictions that they will find highly unpalatable: schools, movies, restaurants, malls, ball games, parks, public pools, libraries, and more, all restricted or outright closed for business. Travel will be frowned upon and perhaps limited. All this will create massive financial strain on the people whose jobs are affected, with ripples spreading out throughout the economy.

I'm predicting that, if a large-scale pandemic does materialize, it will shake the western world's perception of itself to its core. Many people will die. Normal life will be disrupted on a large scale in ways that haven't happened in decades. The economy will be at the bottom of an outhouse before all is said and done. We will learn we are vulnerable to disasters of this scale, despite our assumptions to the contrary.

Stay tuned. The next few months will be very interesting ...

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