Swine Flu: The Morning-After Blues?
As we all come down from last week’s frenzy surrounding the (now renamed for lesser offensiveness to pork-marketing sensibilities) Swine-Origin Influenza Virus (S-OIV) H1N1 , is it possible that there is a hint of disappointment in the air? Perhaps a whiff of anti-climactic letdown after the threat of feverish, lung-rending apocalypse? Are we seeing a lucky escape from a close brush with global pandemic, at mercy of mutation and chance? The product of a genuine, coordinated worldwide epidemic response? Or merely the end of one news cycle and the beginning of the next?
While you ponder those questions, I bring you what could be one of the last updates before S-OIV H1N1 becomes terminally uncool. As of Monday, April 4, the World Health Organization registered 1,085 laboratory-confirmed cases in 21 countries.1 Mexico has begun to step down its safety measures, with restaurants and other venues for public activity set to re-open on Wednesday, and U.S. public health officials will be allowing schools to remain open in spite of the continuing spread of the virus, as most new cases appear to be mild. In the business of assuaging fears, it has been confirmed by the WHO that eating pork is safe (so long as you cook it to 70°C/160°F first), and in the business of fanning fears of a different kind, U.S. conservatives are wasting no time in casting President Obama’s “overreaction” to the crisis as big-government encroachment.
For the fun flu facts reading selection this time, I introduce another global health resource: the University of Pittsburgh’s Supercourse online series on epidemiology and global health. Click on the Swine Influenza A link (or on the image below), pick your language of choice (including Spanish, Russian, Farsi, Vietnamese, and Hebrew), and click “Start” for a refresher on hemagglutinins, neuraminidases, and case definitions.
For a cool overview of influenza virus genetics, check out this article by Carl Zimmer in the New York Times:
Scientists first isolated flu viruses from pigs in 1930, and their genetic sequence suggests that they descend from the Spanish flu of 1918. Once pigs picked up the flu from humans, that so-called classic strain was the only one found in pigs for decades. But in the 1970s a swine flu strain emerged in Europe that had some genes from a bird flu strain. A different pig-bird mix arose in the United States.
In the late 1990s, American scientists discovered a triple reassortant that mixed genes from classic swine flu with genes from bird viruses and human viruses. All three viruses — the triple reassortant, and the American and European pig-bird blends — contributed genes to the latest strain.
And for possibly the best selection of flu-tracking maps you’re likely to find, this one is brought to you by Google and Rhiza Labs:
1 For the epidemiologically-minded, with a lab-confirmed death toll of 26, this makes for a Case Fatality Ratio of 2.4% and falling with every new case of lab-confirmed disease in the absence of further deaths. For comparison, your annual, garden-variety flu has a CFR of less than 0.1% in the general population, with a bimodal distribution of mortality (mostly limited to the very young and the very old). Past flu pandemics have had CFRs in the 0.1%-2.5% range, while the dreaded H5N1 avian flu virus tracked in Asia in recent years showed a CFR of 14%-60% by various estimates (Li et al., J Epidemiol Community Health. 2008 Jun;62(6):555-9 ). One previously reported CFR for zoonotically-acquired swine influenza was 14% (Myers et al., Clin Infect Dis. 2007 Apr 15;44(8):1084-8 ). As you may suspect, flu CFRs are notoriously difficult to calculate, due to the wide incidence and under-reporting of mild cases.
