# Other takes — and a correction — on the Mexico mystery

Via emails, comments, and so on, quite a few people offered their own explanations for why mortality might be higher in Mexico (as of yesterday), the subject of my Slate piece.

First, though, a correction: I punched my numbers a bit too quickly in computing the flue’s hypothetical kill ratios in Mexico, and had everything a decimal point over, and — and therefore tenfold too understated.

“about 100 deaths?suggesting a mortality rate of 6 percent. This is
almost certainly bad math, as the total case count almost certainly
ignores thousands or tens of thousands of other cases that have taken
milder courses like those in the United States. It’s perfectly
conceivable Mexico has actually had 10,000 or 100,000 cases?or even 1
million cases. If so, then the kill rate would be not 6 percent but 0.1
percent (given 10,000 cases) or 0.01 percent (given 100,000 cases). If
it’s 1 million cases (quite possible if this thing really spreads
easily) then the mortality rate is just 1 in 10,000.”

You’re off by a factor of ten. If there were 10,000 cases, then 100
deaths makes 1.0 percent, not 0.1 percent. Similarly, if there were
100,000 cases, then one in a thousand or 0.1 percent (not 0.01) would
have resulted in deaths. You are right that if there were a million
cases, the mortality rate would be one in 10,000 — but that is 0.01
percent.

As these are hypotheticals, the implications are not huge. But worth correcting, for certain.

Several readers wondered whether poorer health-care and less health-care access in Mexico might account for the higher death rate. This obviously could play a role down the line. But for yesterday’s comparison, which really concerned the virulence of the virus rather than treatment outcomes, it probably makes little difference. The question, that is, was not really many how people died but why many people in Mexico were getting extrenely sick while those elsewhere had much milder forms and hardly even needed any significant health care.

One writer — a specialist in nutrition and medicine — wrote suggesting that

1. On the genetics: it is possible that the NEW swine flu would differentially affect different genetic populations. All one needs is for the flu antigen to bind to a receptor, that receptor having different polymorphisms in different populations. We metabolize chemicals produced by human manufacturing, immunity is no different.

2. What about the environment? Some of the populations may be immune compromised by poor diets, air quality, etc. I work in the area of gene – nutrient interactions. It is not genes alone (usually) OR environment alone (usually) but the combination.

I alluded to the air pollution possibility. As to the genetics, this writer may have a point — though, again, my (admittedly rather quick) reading is that few experts feel this is likely to explain a large difference. Perhaps it could make some — but it given the genetic diversity in the U.S. and elsewhere, it would seem little to lean on in terms of reassurance. I’ve no idea how diverse genetically are the various people infected who are now not in Mexico. But given the geographic distrubution, you’d have to figure the diversity is fairly large.

This will all get considered and explored over the next few days.

1. #1 lorraine
April 28, 2009

What about this idea- having lived in Mexico in the countryside and DF itself, with family there as well, it seems possible that very poor record/data tracking could be at the root of this. Perhaps this flu has been around longer than estimated and killing the elderly and infants in quite larger numbers, but the illness did not draw attention until it began to kill the less fragile midddle-aged groups, which, statistically speaking, would happen, alongside of those other groups. Life is far more tenuous in Mexico because of the lack of many things,- medicine, doctors, seatbelts, rubber-covered playgrounds, etc. and Mexicans accept the inevitability of death more readily than we “Americans” in the U.S. Combined with the absence of “first-world” data, this could explain alot, especially at the countryside level.

2. #2 John Gray
April 29, 2009

I may have missed this one,but perhaps the swine flue has mutated and the US strain is less deadly than the Mexican strain?Wouldn’t this make sense?After all a pathogen that kills its host(especially if it kills quickly)has less chance of spreading than a pathogen that merely makes its host ill.
This is the main reason not to get too worked up about Marburg virus:yes,it’s deadly,but unless you are in close contact with someone who is infected,it kills its host before it has much time to infect others.

3. #3 David Dobbs
April 29, 2009

Lorraine: All the factors you name are possible contributors to the obscurity lying over the numbers here.

John Gray: It’s POSSIBLE the virus has mutated to be less virulent — but the several recent deaths reported in Mexico and in Houston (if they prove to be caused by this strain) would argue against it.

And I wouldn’t take too much comfort it the idea of this virus being too deadly to spread. It appears to be contagious for a full day before symptoms show, and to then take 2-10 days to run its course. If it’s transmitted as readily as most flus are by coughs and sneezes, that’s plenty of time for the virus to spread.