Wednesday, December 18, 2013

H7N9: China's Wet Market Mis-Focus and the Beltway Sniper's White Van

In 2002 the Beltway Snipers were randomly killing people;  law enforcement officials and the public were consumed with the (incorrect) hunt for a "white van" that was supposedly spotted at every shooting. Authorities even suggested that if people come under gunfire that those people should run in a zig zag pattern while simultaneously taking notes on white vans near by.

During that epidemiological hunt, apparently no one considered that white work vans were ubiquitous in the Beltway. A very similar situation may be occurring with China's focus on poultry wet markets and the "random" spread of H7N9.  The current (post wet market mitigation) efforts may bear more fruit investigating Streptococcus pneumoniae as a Sentinel of H7N9 infection in daycare centers.

There is little doubt that China's wet markets contributed to spread of #H7N9 during last Spring's outbreak. Our own take is that those markets amplified and served as a source of capacitance for relatively small population of feral propagating H7N9. In essence, the markets were like gasoline to an H7N9 spark; they allowed the disease to multiply in urban areas and spread to urban bird populations.

However, the situation in the wet markets is much less clear this winter. One thing the Chinese have done is to put in place measures that help prevent the spread spread of H7N9 from any particular day's poultry inventory to the next day's new/fresh poultry inventory, making the current situation more akin to putting damp lighter-fluid on a spark..

The wet market risk mitigation actions help reduce the markets' ability to act like an H7N9 amplifier & capacitor, moreover it pushes the FERAL transmission bottle neck back up to the poultry wholesalers and producers.  Given that the there is less massive poultry factory farming in China, there is significantly lower risk of feral H7N9 amplification at that point in the supply chain, but it does come at cost of easily tracing the outbreak back to its source.

The lesser understood risk factor is the size of the human H7N9 reservoir. The Chinese only a test a very small subset of possible Human H7N9 infections. In short, for most people, unless they have an unexplained case of  pneumonia, some proximity to poultry, and are showing flu like symptoms, they will not even get a rapid test for H7N9. If they do meet that criteria, they wont get a laboratory test unless the pneumonia turns severe. And typically, a rapid positive won't be publicly reported unless the later laboratory test comes back positive.

Give those restrictions it is possible there is a large swath of POSSIBLE missed human H7N9 cases (and deaths). The first place to look for those hidden infections might be in people with influenza like illness  (ILI) who also have Streptococcus pneumoniae. These people aren't tested because there is an explainable reason for them to have pneumonia, but that rationale white washes the fact that people with flu are 1000's of times more likely to come down with  Streptococcus pneumoniae. Unfortunately, it just so happens there is just such an ILI -Streptococcus pneumoniae outbreak going on right now in China, especially in school age children.

One thing to recognize in any war, public health or otherwise, is that the General's are always preparing to fight the previous war again; and that may be the case with the H7N9 risk mitigation efforts in China. The wet markets are important but they MAY no longer be the most efficient or cost effective target in the spread of H7N9.

The fact is that the testing and diagnosis criteria for H7N9 is self referential for wet market exposure, as such its epidemiological sleuthing significance drops off quickly once effective risk mitigation has been applied. As it stands now in China any hospital sickness or injury can be tied to the consumption of chicken or exposure to wet markets, as these are a ubiquitous cultural way of life.

Its much the same as tying any American's use of toilet paper to a particular sickness or injury; ask any American checking into a hospital  if they have recently used toilet paper and the answer will be yes. Much the same can be expected when asking someone in a Chinese hospital if they or someone they know has recently been to a wet market or eaten chicken.

None of this degrades the need for further wet market vigilance, but it does speak to the likelihood that opportunity costs of targeting other low hanging infection fruit may be have much greater return than a laser like risk mitigation focus on the wet markets.

We see the current state of H7N9 epidemiology as much akin to the hunt for the White Van the Beltway Snipers were supposedly using. Many a resource was wasted and many a van driver was dangerously inconvenienced when the real hunt should have been for a 1990 blue Caprice. To a lesser extent, this same phenomena may be occurring with Chinese wet markets today, and we'll make a wager that shutting down urban daycare and kindergartens will have a greater impact on today's spread of H7N9 than further mitigating the wet markets via shutdown.

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