The Morbidity and Mortality Weekly Report (MMWR) has posted two dispatches that offer the most detailed looks yet at two outbreaks of what's now being called swine-associated H1N1 influenza. One report focuses on Mexico and the other on a school in New York City. The Mexico report says there is a confirmed case that had an onset of symptoms on 17 March, making it the earliest yet found anywhere in the world. Although the U.S. Centers for Disease Control and Prevention publishes MMWR, CDC officials at a press conference today said they had no information about this apparent "index" case of the outbreak. Index cases can play a critical role in understanding an outbreak's origins.