CBS News Medical Contributor Dr. David Agus joined WCBS' Steve Scott to explain the details on this nasty bug.PHOTO: Number of Gram-negative Escherichia coli bacteria of the strain O157:H7, revealed in the 6836x magnified scanning electron microscopic (SEM) image, 2006. Image courtesy Centers for Disease Control (CDC) / National Escherichia, Shigella, Vibrio Reference Unit at CDC. (Photo by Smith Collection/Gado/Getty Images)