SCIENCE
October 30, 2009 | By Thomas H. Maugh II
Between 1.8 million and 5.7 million Americans caught pandemic H1N1 influenza this spring, as many as 21,000 were hospitalized, and perhaps 800 died, according to new estimates by researchers at the Centers for Disease Control and Prevention. The revised numbers suggest that even larger numbers will become infected during this flu season. Estimates, as opposed to specific numbers, are the best data available. Many cases are not reported to public health authorities, and the CDC stopped requiring laboratory confirmation of new cases when labs were becoming overwhelmed.