About 11,000 Americans have died of swine flu as of last month, the Centers for Disease Control and Prevention said. The agency’s previous estimate — for deaths from April, when the virus was discovered, to mid-November — was about 10,000. Because the second wave peaked in late October, the number is unlikely to rise much unless there is a third wave later this winter. The estimate by the World Health Organization as of Jan…. 3 was 12,799 deaths worldwide. The two numbers are not directly comparable because the W.H.O. counts only laboratory-confirmed deaths. Only a small fraction of all flu cases are tested by laboratories, especially in poor and middle-income countries, and many deaths that the flu causes are officially given other reasons, like pneumonia or heart failure.