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WHO spokesperson Gregory Hartl recently spoke of the difficulties in pinpointing the vector of human transmission of H7N9. This is from an Investor Business Times article from last Thursday:

“This is one of the puzzles still [to] be solved and therefore argues for a wide investigation net,” Hartl said. “It might be because of dust at the wet markets, it could be another animal source beside poultry, it could also be human-to-human transmission,” he said.

The idea of "dust" is not a far-fetched one, but it does warrant some explanation.  We know that viruses are also subject to the laws of gravity.  Virus particles will, inevitably, drop to the ground -- only to be kicked back up again when disturbed.  I alluded to this in an older post, from 2007.

During the SARS almost-pandemic, vacuuming of hotel carpets in China contributed to the spread of the disease.  The cruise ship industry's protocol when confronted with an outbreak of norovirus on a ship at sea includes the cessation of vacuuming.  And my lectures and presentations on pandemic preparations include this same advice.

It is entirely possible that "dust" from the floors of wet markets might have contributed to the incidence of human cases, but it still would not point us toward the source of the infections. Something/someone had to deposit that "dust" on the floor of the market. Clearly, the WHO feels that poultry remains the most likely candidate.  However, continued testing of poultry from wet markets in Shanghai and elsewhere have failed to find the "smoking chicken" everyone desperately needs to find, before this virus goes through enough mutations for find -- voila! -- a branch of this flu with the ability to move at will amongst humans.

And if the culprit is not poultry, then is there another vector depositing virus on the floors of, say, bus depots, other markets, hotels, restaurants, or newsstands?