More flu news

The first death outside of Mexico has been reported:

The first death in the United States from swine flu was reported on Wednesday, as the number of confirmed and suspected human cases worldwide continues to rise following an outbreak in Mexico.

The U.S. Centers for Disease Control and Prevention in Atlanta said on Wednesday that swine flu caused the death of a 23-month-old child in Texas. It is believed to be the first death outside Mexico.

Dr. Richard Besser, the CDC's acting director, confirmed the death during an interview with CNN on Wednesday. No further details about the child or the circumstances of the death were provided.

From here. This is not in keeping, though, with the pattern of mortality in Mexico, where (worryingly) a disproportionate number of deaths, as noted previously, have been young adults. Slate has an article examining possible reasons for the differences between Mexico and the rest of the world in the way the flu is impacting them. They propose four:

1) Perhaps population-level genetic differences render the U.S. population more resistant to this strain's effects than the Mexican population.

The author considers this unlikely for the following reason:

This isn't like the smallpox situation of 500 years ago, when American Indians were decimated by a virus they'd never encountered while Europeans carried it easily because centuries of exposure had selected them for resistance. This strain of swine flu virus is apparently new to everyone—a combination of bird flu, seasonal human flu, and (predominantly) two kinds of swine flu, all in a form our bodies have never seen. There seems no reason any human population should resist its effects substantially better or worse than any other.

To this one could add the fact that many Americans have Mexican ancestry. There doesn't seem to be any data on the ethnicity of cases from the rest of the world, but I would expect that at least some of the infected had visited family in Mexico.

2) We're really looking at two different viruses, but WHO and the CDC haven't picked up on it.

So far, tests have failed to find any difference in the viruses from the fatal cases in Mexico and the less severe cases elsewhere. It's possible that some subtle difference exists that the tests haven't detected, but it seems less likely owing to the heavy scrutiny the virus is being placed under.

3) Some secondary health issue present in Mexico but not elsewhere—another bug common in the population or in hospitals—is combining with the swine flu to make it more deadly there.

Quite plausible. Either another infection (perhaps bacterial) could be complicating matters, or the severe air pollution in many parts of the country may make people more susceptible to lung damage, or both. The air pollution hypothesis could be effectively tested if an infected person turned up in another highly polluted place (like Beijing), but so far Asia seems to have avoided infection, and let's hope it stays that way.

4) Some difference in the way we're tracking and counting cases—a "surveillance difference"—is making the Mexico situation seem worse than it is and the U.S. situation seem better than it really is.

In other words, there have been a lot of mild cases in Mexico as well, but they've flown under the radar. This is extremely plausible, because if the actual mortality rate is very low you wouldn't likely see many deaths (if any) among the relatively small number infected in the rest of the world. And, as the article points out, this outbreak emerged during Mexico's regular flu season, so a lot of mild to moderate cases would not have seemed unusual before the discovery of this strain.

So we don't really know. I guess all we can do is stay tuned.