POLIO VIRUS FOUND IN U.K. SEWAGE SAMPLES

Health authorities in Britain have declared a national incident after finding evidence suggesting local spread of poliovirus in London.

No cases of polio have been identified so far, and the risk to the public is low. But health authorities urged anyone who is not fully immunized against poliovirus, particularly young children, to immediately seek vaccines.

The last case of polio in Britain was in 1984, and the country was declared poliofree in 2003. Before the introduction of the polio vaccine, epidemics were common in Britain, with up to 8,000 cases of paralysis reported every year.

Routine surveillance of sewage in the country picks up poliovirus once or twice a year, but between February and May, officials identified the virus in several samples collected in London, according to Dr. Shahin Huseynov, technical officer for the World Health Organization’s vaccine-preventable diseases and immunization program in Europe.

Genetic analysis suggests that the samples have a common origin, most likely an individual who traveled to the country around the new year, Huseynov said. The last four samples collected appear to have evolved from this initial introduction, likely in unvaccinated children.

British officials are now collecting additional samples and trying to identify the source of the virus. But the wastewater treatment plant that identified the samples covers about 4 million people, making it challenging to pinpoint the source.

Polio is spread most often by an infected person who does not properly wash their hands and then touches food or water ingested by someone else. In up to 1 percent of patients, the virus can infect the spine and cause paralysis.

In Britain, immunization for polio is carried out with an injected inactivated poliovirus, which cannot be shed through feces. But some countries rely on an oral polio vaccine that contains a live, weakened version of the virus. Immunized people can briefly shed this virus in their feces, which can then turn up in sewage.

The virus in the collected samples came from a type of oral polio vaccine that is used to contain outbreaks, according to Huseynov. In recent months, that type of vaccine has been used only in Afghanistan, Pakistan and some countries in the Middle East and Africa, he said.