TO THE EDITOR—As of 30 May 2013, the novel avian influenza A(H7N9) virus has caused 132 laboratory-confirmed infections, with 37 fatal cases . As the temperature went up, the reported number of infections naturally declined, with only 3 cases reported in May 2013.
As of 4 June 2013, 36 genome sequences of the novel H7N9 viruses have been deposited in the GISAID database (Global Initiative on Sharing All Influenza Data; www.gisaid.org). Using all of the 36 genome sequences, we calculated the nucleotide substitution rates for each of the 8 gene segments with the single likelihood ancestral counting method . Surprisingly, the substitution rates of the internal genes (except for PB2) were very high, with a similar magnitude to those of surface protein coding genes HA and NA (Figure 1A). In particular, the substitution rates of the M2 and NP genes were even higher than those of HA and NA.