A new strain of swine flu has shown up in two children in Pennsylvania and Indiana who had direct or indirect contact with pigs, the Centers for Disease Control and Prevention (CDC) reported Friday. The virus includes a gene from the 2009 pandemic strain that might let it spread more easily than pig viruses normally do. There is not yet any sign that the virus has spread beyond the two children. "We wanted to provide some information without being alarmist," because people have contact with pigs at fairs this time of year and doctors should watch for possible flu cases, said Lyn Finelli, the CDC's flu surveillance chief. "We're always concerned when we see transmission of animal viruses to humans." People rarely get the flu from pigs - only 21 cases have been documented in the last five years - and it is too soon to know how infective this virus will be, she said.