Keep our eyes peeled indeed. This swine strain, serotype H1N1 (the "classic" swine flu serotype) is apparently a triple reassortant, carrying genes from human, swine, and avian influenza viruses. A few things make this outbreak concerning.
One, we see occasional swine influenza infections in humans on a somewhat regular basis. There was an outbreak associated with a fair in Ohio a few years back, and research by my colleague Greg Gray here at the university has showed that mild or asymptomatic infections of swine workers with swine influenza viruses are more common than we realize (David Brown of the Washington Post has a nice summary of that background here). However, those infected in California and Texas have no known contact with pigs--suggesting they acquired this virus from a human source.
Two, while the cases in the US have been mild and no deaths have occurred that we're aware of, it seems in Mexico that young people are dying from this--a group that is typically not hard-hit by seasonal influenza viruses. Readers familiar with influenza and know the history of the 1918 influenza pandemic will recall that the "young and healthy" were disproportionally struck by that virus as well--so this knowledge is currently disconcerting and worrisome, but there are so many gaps in our information as far as what's really going on in Mexico that it's difficult to make heads or tails out of this data right now.
Third, is this really a new virus? So few influenza isolates are actually analyzed each year (in proportion to the number of people infected) that we aren't sure yet whether this is something brand-new, or something that has been circulating at a low level for awhile, but just hadn't been picked up. After all, H1N1 is a common serotype, so additional molecular testing is needed to determine that it's "swine flu" versus "human" H1N1.
Fourth, and going along with that third point--how widespread is this? We have confirmed cases from Mexico, California, and Texas, which suggest it could be spreading in the southern parts of North America--but a breaking news report says that cases have also been confirmed in Kansas and New York, but it doesn't say whether they've been definitively matched to the strains from the SW US and Mexico. The NY Times reports that some students at the NY school had recently traveled to Mexico and could have potentially brought the infection back from that trip, if it's confirmed.
