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In Turkey a large number of patients were hospitalized with bird flu symptoms. The patients were from large familial clusters and the number of familial clusters has been large.

These data alone signal an increased efficiency in the ability of H5N1 to infect people, regardless of source, which could be birds or humans.

This increased ability is supported by two genetic changes, the HA S227N (also called S223N), which allows for more efficient recognition of binding sites on epithelial cells that line the human respiratory tract, and PB2 E627K, a change that allows H5N1 to grow at lower temperature (34 C), which is the temperature inside a human nose outside in the winter.

The presence of both changes in the same virus has not been previously reported.

In Turkey, the true picture of H5N1 infections is clouded by false negatives and limitations in testing of advanced patients.

The first four suspects, the Kocigit siblings, all tested negative by PCR testing of nose and throat swabs. Three patients have died, and subsequent testing of lung samples have been positive.

One isolate, from the oldest brother, has been obtained and fully sequenced. The sequence identified the S227N change and the explosion of cases in Turkey strongly suggests the change is present in the wild bird population.

The true number of H5N1 patients is not publicly known.

Data from prior clusters show a 5-10 day gap in almost every familial cluster, indicating all or most are examples of horizontal transfer between humans.

Although such data has not been provided in WHO reports, media reports suggest similar gaps between onset dates are present in the clusters from Turkey.

Such gaps would be expected, since H5N1 is clearly efficiently transmitted to humans based on the number of confirmed cases, the number of suspected case, the size of the clusters, and the number of clusters.