Polio may have been spreading in New York since April

A new study from the C.D.C. provides more details on a polio case detected in New York last month and suggests the virus has been spreading elsewhere for a year.

Polio may have widely circulated for a year, and was present in New York City wastewater as early as April, according to a new report from the Centers for Disease Control and Prevention.

A sample of waste collected in April in Orange County, N.Y., tested positive for the virus, pushing back the first known detection in the area. Authorities previously announced that the virus was found in sewage samples from May in neighboring Rockland County.

Changes in the genome of the virus suggest that this version has been circulating, somewhere in the world, for up to a year. Genetically similar versions of the virus were detected in Israel in March and in Britain in June.

The new study provides more details on an ongoing investigation into a A polio case was detected in New York last month when authorities announced that a young adult in Rockland County had become paralyzed from polio. This was the first report of polio in the United States since 2013.

The results are not entirely surprising, especially since polio, which is highly contagious, often spreading without causing serious symptoms, said Joseph Eisenberg, an infectious disease epidemiologist at the University of Michigan. "It can circulate quite widely, being under the radar, before you start seeing cases of paralysis," he said.

Officials had previously warned the Rockland County patient was most likely the "tip of the iceberg".

Polio vaccination rates are just 37% in select county zip codes, the new study found.

The patient, who had not been vaccinated against polio, was hospitalized in June after developing symptoms such as fever, stiff neck and weakness in the lower limbs, according to the study. The poliovirus, which is spread mainly through feces, was later detected in the patient's stool.

Genomic sequencing revealed that the patient was infected with a version of the virus derived from the oral poliomyelitis vaccine, which contains a weakened version of the virus. The oral vaccine has not been used in the United States since 2000. (American children are routinely immunized with an injected vaccine.)

The oral vaccine is safe and effective , but people who receive it can shed the weakened virus in their stool for weeks, potentially infecting others. In communities with many unvaccinated people, the virus may continue to circulate and eventually acquire enough mutations to become dangerous again.

The discovery of the Rockland case prompted the health experts to begin testing sewage samples taken from the area, including those that had already been taken for coronavirus monitoring.

Officials had previously announced that it had found the virus in 20 sewage samples taken from Rockland and Orange counties and that all had been genetically linked to the patient sample.

The A new study found that a 21st sample, taken from Orange County in April, also tested positive for the virus. However, there was insufficient genomic information available to establish a conclusive link to the other samples.

Two hundred and sixty sewage samples from the counties of Rockland and Orange had been tested on August 10, and polio was detected in 8% of them, according to the new study.