Polio has been considered eradicated in the United States since 1979, but since April this year, local authorities have found traces of the virus in sewage, AFP reports.
The emergency situation means that work on vaccination can be stepped up and the goal is a vaccination rate of 90 percent instead of today's 79 percent, according to the BBC.
In June, the British health authority also found traces of poliovirus in London's sewage, which has prompted the EU's infection control authority ECDC to react.
The authority is now warning that the disease, which has been eradicated throughout Europe since 2002, will return.
Countries are encouraged to review their vaccine coverage and, if necessary, increase it.
The disease, which is also called polio, has previously been behind countless cases of death, paralysis and lifelong disabilities, especially in poorer countries.
In Sweden, mass vaccination against polio began in 1957 and the last domestic case was reported in 1977. Since 1965, polio vaccine has been included in the general childhood vaccination program.