USDA announced yesterday that the 4th confirmed case was confirmed yesterday in a Dairy cow in Central California. The cow was tested at a rendering facility and the meat from that cow was not bound to enter the human food supply chain. The animal has been condemned and will be destroyed.
Here is a link to a web site that has some great information on what BSE is, how we are monitoring it in the US cow herd, the safe guard system to detect and prevent high risk animals from entering the food supply.
Here is the video of the USDA's chief veterinarian speaking during the announcement.
China, Japan and the EU have all stated that they will not halt imports of beef from the US.