FRIDAY, May 15 (HealthDay News) -- While the official tally of confirmed U.S. swine flu cases topped 4,700 on Friday, experts at the Centers for Disease Control and Prevention now estimate the true number of infections at more than 100,000 nationwide. [snip] In fact, "estimates of the confirmed and probable cases in the United States is probably not the best indicator of transmission at this point," the CDC's Jernigan said. "The outbreak is not localized, but is spreading and appears to be expanding throughout the United States. This is an ongoing public health threat," he said. It's a little hard...