Post-polio syndrome, it turns out, is not a new disorder after all. It was described in the French medical literature in 1875, and then, as often happens in medicine, it was forgotten. Over the next 100 years, approximately 35 reports on post-polio weakness were published in the medical literature. By 1984 a growing awareness of the delayed effects of polio prompted me and other researchers to organize an international conference at the Warm Springs Institute for Rehabilitation--the great polio treatment mecca 6 in southern Georgia established by Franklin Delano Roosevelt, who was paralyzed by polio in 1921 at the age of 39. Roosevelt felt that swimming in the warm waters of a natural spring at a health resort strengthened his muscles, and in 1926 he purchased a hotel there and turned it into a nonprofit foundation.

A second international meeting on post-polio syndrome was held at the Warm Springs Institute in 1986, and in the following years there was a dramatic increase in basic and clinical research into the long-term effects of polio. In 1994 the New York Academy of Sciences and the National Institutes of Health cosponsored another international meeting that culminated in the publication of a special issue of the Annals of the New York Academy of Sciences: "The Post-Polio Syndrome: Advances in the Pathogenesis and Treatment." That conference signaled the acceptance of post-polio syndrome as a legitimate clinical entity.

Surprisingly, accurate figures about the number of Americans who have had paralytic polio are not available and probably never will be. There is no national registry of persons who were diagnosed with the disease, and there is no way, after all these years, to compile accurate figures from state and local health departments. The best estimate is based on information from the federal government's National Center for Health Statistics, which collects data on health and disability issues every year from a random sample of U.S. households. Based on data from the 1987 survey, the National Center for Health Statistics calculated there were more than 640,000 survivors of paralytic polio, which would mean there are more survivors of paralytic polio than there are persons with multiple sclerosis, amyotrophic lateral sclerosis or even spinalcord injury.

Since 1987 an unknown number of polio survivors have died, but immigrants, refugees and illegal aliens have added an unknown number to the U.S. population of polio survivors. No one knows how many survivors of paralytic polio have post-polio syndrome. Some studies indicate the figure could be as high as 40 percent. If this estimate is accurate, then the total number of persons in this country currently suffering from post-polio syndrome could reach 250,000.

Knowledge of how the poliovirus infects the body can be helpful in understanding the possible causes of post-polio syndrome. It is a small RNA virus that can enter the body when contaminated water or food are ingested, and even when contaminated hands touch the mouth. The vast majority of persons who become infected either have no symptoms or experience a self-limited illness characterized by fever and gastrointestinal upset for several days. The poliovirus, which replicates in the lymphoid tissue of the throat and small intestine, either passes harmlessly from the gut or travels in the blood to all parts of the body. In a small minority of infected persons--usually 1 to 2 percent--the virus invades the central nervous system and produces an unpredictable amount of paralysis.