The scientists examined outbreaks in European fur farms, South American marine mammals, and US dairy cattle.
California now has 40 avian flu outbreaks in dairy herds, and the US total has reached 238.
In other developments, CDC and Ohio partners launched a serosurvey among bovine veterinary workers who attended a recent professional conference.
The source of the girl's infection isn't known, though H9N2 has been reported in the country's poultry before.
California now has the nation's second most dairy farm outbreaks.
In other H5N1 developments, the FDA's vaccine advisory group said it will discuss the composition of H5 vaccines when it meets next month.
Massachusetts is the only state to test all dairies, which involved bulk-milk tank sampling in August.
Like most other H9N2 cases, China's latest illness involves a young child.
Also, sequencing confirmed N1 and identified two HA mutations, one of which could affect vaccine development.
Afghanistan's polio vaccine campaign raises concerns, given that WPV1 is endemic there and cases are rising.
