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Excerpt from the
Handbook on the Late Effects of Poliomyelitis for Physicians and Survivors©

Epidemiology

Epidemiology is the study of disease in populations or groups rather than in individuals. Epidemiological studies provide important information about frequency, distribution, and the risks of developing a certain type of problem.

Many studies of polio survivors have been done on small, select populations such as individuals who seek treatment at a post-polio clinic, members of a support group, or subscribers to a newsletter. Due to this self-selection, the results often are questioned. Another criticism is the lack of data from longitudinal studies.

A few studies have been completed in which survivors were randomly selected from the population. One study of polio survivors in Olmsted County, Minnesota, between 1986 and 1993, identified 50 individuals who had had paralytic polio between 1935 and 1960. (They were representative of the total of 300 cases of paralytic polio in the county.) Detailed clinical and nerve function tests were carried out at the beginning and after five years. These studies demonstrated stable nerve and muscle function within this group. Although there were no signs of progressive paralysis, 60% of the survivors did report combinations of symptoms of pain, increasing weakness, and fatigue. In two-thirds of the symptomatic individuals, the causes of their symptoms were unrelated to earlier polio and were able to be treated. Overall, 20% of the individuals had muscle pain, perception of weakness, and fatigue, even though they did not have measurable progressive loss of muscle function (Windebank et al., 1996).

A population-based study from Allegheny County, Pennsylvania, using a survey validated by clinical examination, found a prevalence of 28.5% of post-polio syndrome in all paralytic cases. The risk was higher in individuals who experienced substantial permanent impairment after polio and in females. The strongest indicator was the polio/post-polio interval - not age at acute onset, acute severity, or level of physical activity after recovery. Incidence peaked at 30-34 years post-onset (Ramlow et al., 1992). It should be noted that exceeding that interval does not exempt one from future post-polio problems.

A 1987 National Health Interview Survey (NHIS), conducted in the United States, collected information from 821 polio survivors found in 50,000 households (120,000 people). The resulting estimate was of 1.6 million polio survivors, with 640,000 of them survivors of paralytic polio. The preliminary data from the 1994-95 NHIS (445 respondents) estimates 1 million polio survivors with 430,000 described as survivors of paralytic polio. The extensive survey traces the natural history of poliomyelitis and includes numerous questions about the "period of personal best," as well as the current period to capture the amount of decline, if any.

In a 1990 survey of 3,607 Danish paralytic polio survivors (estimated population of 7,200), the three most frequent complaints were considerable fatigue during exercise (59% in men; 76% in women), considerable weakness in previously affected muscles (52% in men; 67% in women), and joint pain (46% in men; 64% in women), with fatigue being the most common new symptom in both sexes (Lønnberg, 1993).

A 1994 Norwegian study (2,392), believed to be representative of all polio survivors in Norway, showed that 50% were experiencing new health problems related to their polio and reported an increased need for technical aids, personal assistance, and multidisciplinary health services (Wekre et al., 1998).

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