The last case of paralytic polio in the United States caused by wild poliovirus was reported in 1979. Between 1979 and 2000 (when use of the oral polio vaccine was stopped in the U.S. and many developed countries), an average of five new cases of paralytic polio were reported each year. In 2022, an unvaccinated man in New York contracted acute polio—the first such case in the U.S. in nearly a decade. Polioviruses, however, are not the only agents capable of causing paralytic syndromes similar to classic poliomyelitis. There are at least six different viruses that can cause poliomyelitis-like paralysis. The clinical picture of paralytic poliomyelitis can also be mimicked by other syndromes, the most common of which is Guillain-Barré syndrome (GBS) or acute flaccid myelitis (AFM).
Sometimes individuals with other cases of muscle weakness or disability were diagnosed as having polio when they did not because of the lack of yet-to-be-discovered sophisticated imaging devices, such as CT or MRI, a belief that children did not have conditions such as stroke, or by well-meaning physicians who knew that if they diagnosed an uninsured child with “polio” their medical care could then be paid for by the March of Dimes.
Others had mild paralysis that may not have been noticed by the family or even medical professionals, especially in children under the age of one, and thus were not diagnosed at the time. The diagnosis of polio may be made years later by a combination of new symptoms consistent with PPS and the characteristic findings of previous polio on EMG.