At least two influenza strains will infect people in the United States this winter, federal health officials in Atlanta said, and the first cases have already been reported in three states. A flu virus known as A-Leningrad has been identified in patients in California, South Dakota and Wyoming, the national Centers for Disease Control said. The A-Leningrad has historically caused higher death tolls and more hospitalizations and absenteeism than the other two current types of influenza, B-Ann Arbor and A-Taiwan. Nancy Arden of the CDC said that A-Leningrad and influenza-B "will be the predominant strains this winter." She said it is also possible that A-Taiwan will return again this year.