The virus that causes polio has been found in New York City's wastewater in another sign that the disease, which hadn't been seen in the U.S. in a decade, is quietly spreading among unvaccinated people, health officials said Friday. 

The presence of the poliovirus in the city's wastewater suggests likely local circulation of the virus, health authorities from the city, New York state and the federal government said. 

The authorities urged parents to get their children vaccinated against the potentially deadly disease. 

"The risk to New Yorkers is real but the defense is so simple – get vaccinated against polio," New York City Health Commissioner Dr Ashwin Vasan said. "With polio circulating in our communities there is simply nothing more essential than vaccinating our children to protect them from this virus, and if you're an unvaccinated or incompletely vaccinated adult, please choose now to get the vaccine. Polio is entirely preventable and its reappearance should be a call to action for all of us."

Dr José R. Romero, director of the Centers for Disease Control and Prevention's National Center for Immunization and Respiratory Diseases, said, "This is sobering; we know polio spreads silently, and it's likely that there are many people infected with polio and shedding the virus in these communities. This is also an urgent and living reminder of the importance of vaccination."