China and the World Health Organization reported, as of May 8, there were 131 confirmed cases of H7N9 -- bird flu, or avian flu -- with 32 deaths.
Studies indicated avian influenza viruses have a seasonal pattern to them, similar to human seasonal influenza viruses, the CDC said.
"After watching H5N1 for more than a decade, it's clear that activity in poultry -- and resulting human infections -- increase in the winter and decline in the summer," the CDC statement said. "It's possible that the same will be true with H7N9 and that as H7N9 activity in poultry or other birds declines, so will the chances for human exposures and resulting human infections. If this is the case, H7N9 infections -- in birds and people -- might pick up again when the weather turns cooler."
The number of human infections being reported has dropped, the epidemiology of the current outbreak has not changed significantly, health officials said.
Evidence continues to point to infected poultry or contaminated environments as the source of most infections. There is still no evidence of sustained human-to-human transmission with this virus and no cases have been reported outside of China, the CDC said.