While California reported 12 dairy herd bird flu outbreaks last week, most states have not reported a new case in weeks. Agriculture Deputy Undersecretary Eric Deeble said there is confidence that the virus can be eliminated by isolating the herds.

The USDA strategy is to step up biosecurity measures and isolate infected herds until the infection dies out. Colorado leads the nation with 64 infected herds, but the last outbreak was reported on August 13. Michigan was third in the country with 64 infections. The last reported outbreak was on September 9.

California is second in the nation for outbreaks, accounting for a fifth of the 256 herds. Virologist Rick Bright is concerned the virus may be mutating. In California, 10% to 15% of infected dairy cows die. This is a much higher mortality rate than the 1% to 2% reported in other states.

Read more on the bird flu in dairy cattle here.