Mohonk Mountain House, a resort 90 miles north of New York City, is closed while crews sanitize the facilities after an outbreak of gastrointestinal illness. Jim Smith/AP hide caption

itoggle caption Jim Smith/AP

People line up at a Duane Reade pharmacy in New York behind a sign announcing the recent flu outbreak. Andrew Kelly/Reuters/Landov hide caption

itoggle caption Andrew Kelly/Reuters/Landov

An electron micrograph of human norovirus. Charles D. Humphrey/CDC Public Health Image Library ID 10708 hide caption

itoggle caption Charles D. Humphrey/CDC Public Health Image Library ID 10708