A polio case in Rockland County, New York, may be the "tip of the iceberg," state Health Commissioner Dr. Mary T. Bassett warned Thursday, after officials said wastewater samples had detected the virus in an adjacent county.
Urging unvaccinated residents to get immunized against the virus, Bassett said there was the potential for "much greater" community spread.
“Based on earlier polio outbreaks, New Yorkers should know that for every one case of paralytic polio observed, there may be hundreds of other people infected,” she said in a statement.
Last month's case of polio in Rockland County, north of New York City, was the first in the United States in nearly a decade. Polio was detected in the county's wastewater before the patient’s case was confirmed, officials have said.
On Thursday, officials revealed that the virus had also been detected in wastewater samples in Orange County. The samples were taken in June and July from two "geographically different" locations in Orange County, they said.
The majority of polio cases are asymptomatic, but the illness can be life-threatening, can cause paralysis and has no cure.
While there are no additional confirmed cases of polio in Rockland or Orange counties, the area lags behind the statewide average in its vaccination rates, according to state health department data.
Polio is highly contagious, with children under 5 at greatest risk, though anyone who is unvaccinated is susceptible.
Vaccines became widely available in the 1950s and 1960s and have been effective at preventing polio.
The Rockland County patient was unvaccinated, according to officials.
Based on the patient's strain of the virus, the infection is believed to have been transmitted from someone who had been inoculated with a weakened live vaccine, which is not administered in the United States. In rare instances, people who receive this version of the vaccine, which is given orally, can go on to shed viral particles that can infect unvaccinated individuals.
The wastewater findings announced Thursday included three samples from Rockland County and four from Orange County, all of which the Centers for Disease Control and Prevention analyzed and found to be genetically linked to the Rockland County case.
"These findings provide further evidence of local — not international — transmission of a polio virus that can cause paralysis and potential community spread, underscoring the urgency of every New York adult and child getting immunized," officials said in a statement.