NEW YORK (AP) – Oakland County, Michigan, and Philadelphia are joining the small list of U.S. localities that are looking for signs of polio infections in sewage.

The Centers for Disease Control and Prevention on Wednesday announced the expansion.

The two communities will collect and test local sewage for polio for at least four months.

Some places in New York state began testing earlier this year after a man was diagnosed with paralytic polio outside New York City.

CDC officials say they have been talking with other communities about also starting polio wastewater testing.