Workers at the Crosstex corporation, a maker of surgical masks and other medical-industry products, in Hauppauge, in the Town of Islip, on Long Island, have been especially busy with the outbreak of swine flu. The company has been running its production line 24/7, doubling its output of surgical masks, most of which have been sent to Mexico. Crosstex is one of just a handful of remaining U.S. manufacturers of face masks, and the only one in the Northeast.