Influenza A(H7N9) isolates from a second wave of the 2013-2014 epidemic in China were genetically different than those in the first wave, according to researchers at the Guangdong Provincial CDC in Guangzhou, China.

In this epidemic, 401 people were infected with the novel avian influenza A(H7N9) in China. The first wave occurred from February to May 2013; 133 patients had laboratory-confirmed H7N9, 45 of whom died.

According to previous research, six of the eight H7N9 virus segments were acquired from H9N2, and required at least two steps of sequential reassortment. Because nearly all of the analyses to date have been performed on isolates from the first wave, little is known about virus changes in the second wave. The investigators analyzed data for 15 H7N9 viruses isolated from patients in Guangdong from November 2013 to January 2014.

The results of phylogenetic analyses of whole-genome sequence demonstrated that isolates from the second influenza A(H7N9) wave in Guangdong were genetically different in five of the eight RNA segments compared with those in the first wave. Five segments were highly similar to locally circulating subtypes of H9N2, suggesting that rapid and continued reassortment during the second wave, according to the researchers.