New York City health officials announced last week that they detected polio in wastewater, suggesting that the dangerous virus is silently spreading within the nation’s most populous metropolis. The spotting happened about a month after nearby Rockland County became the first American locale in nearly a decade to report a symptomatic case of polio. The virus is also cruising through sewage in Orange County, which sits next to Rockland in the Hudson Valley. For decades, the country hasn’t had to worry about community transmission of polio. Thanks to childhood vaccination, most people in the U.S. have been protected for 70 years, and homegrown outbreaks were eliminated from both North and South America by 1994. To read the full story.