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No additional U.S. cases of poliomyelitis have been identified, according to a new CDC report detailing the nation's first case in nearly a decade, but wastewater specimens in multiple New York counties indicate community transmission and ongoing risk for paralysis in the unvaccinated.

Following stool sample testing, poliovirus was confirmed in June in an unvaccinated young adult from Rockland County, New York, representing just the second case of local transmission in the U.S. since 1979.

The patient had initially experienced fever, neck stiffness, gastrointestinal symptoms, and weakness in the limbs, and was hospitalized for possible acute flaccid myelitis (AFM), reported Ruth Link-Gelles, PhD, of the CDC's Domestic Poliovirus Emergency Response Team, and colleagues in the .

As part of national AFM surveillance, the New York State Department of Health reported the case to the CDC in July.

The patient was possibly exposed 8 days before symptoms started while attending a large gathering. The patient first experienced limb weakness on day 3, and on day 5, the patient was admitted to the hospital. Poliovirus type 2 was detected in the patient's stool on days 11 and 12, and on day 16, the patient was discharged to rehabilitation.

As of this month, 260 wastewater samples from treatment plants in Rockland and Orange Counties were tested for poliovirus, including samples that had been collected to test for SARS-CoV-2. Of these samples, 21 yielded positive results for poliovirus using RT-PCR and partial genome sequencing, including 13 from Rockland County and eight from Orange County.

Among wastewater samples collected during May, June, and July, 20 specimens were genetically linked to poliovirus from the patient's stool samples. Furthermore, one sample from April in Orange County was sequenced as poliovirus type 2, but the sequence was incomplete, which prevented the researchers from genetically linking the sample to the patient.

Further tests of wastewater collected 41 days after onset of the patient's symptoms continued to detect the virus.

"The occurrence of this case, combined with the identification of poliovirus in wastewater in neighboring Orange County, underscores the importance of maintaining high vaccination coverage to prevent paralytic polio in persons of all ages," Link-Gelles and colleagues wrote.

Three additional individuals have been classified as persons under investigation; however, available specimens have yielded negative results.

"Unvaccinated persons in the United States remain at risk for paralytic poliomyelitis if they are exposed to either wild or vaccine-derived poliovirus; all persons in the United States should stay up to date on recommended poliovirus vaccination," they noted.

According to the New York State Immunization Information System, coverage with the three-dose polio vaccine among infants and children younger than 2 years living in Rockland County was 67% in July 2020, which decreased to 60.3% by this month. Zip code-specific vaccination coverage was "as low as 37.3%," noted Link-Gelles and coauthors.

Despite a brief increase in polio vaccination following an attempt by the Rockland County Department of Health to catch up the local population, "the number of doses administered at temporary and established clinics was not sufficient to meaningfully increase population [inactivated polio vaccine] coverage levels," they added.

The origin of the virus found in the patient's stool sample and in wastewater is unknown. However, "the patient's stool samples indicates a chain of transmission within the United States originating with a person who received a type 2-containing oral polio vaccine (OPV) abroad."

Since the infected patient had not traveled internationally within the virus incubation timeframe, and the oral polio vaccine has not been part of routine immunization schedules in the U.S. since 2000, the origin of the virus is difficult to track.

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