A late-onset syndrome, consisting of muscle weakness, muscle pain, and unaccustomed fatigue, has been reported with increasing frequency among former poliomyelitis patients. A population-based cohort of poliomyelitis patients from Allegheny County, Pennsylvania, was traced and surveyed to estimate the prevalence and incidence and to identify determinants of the post-polio syndrome. A questionnaire validated in clinical examinations of 40 cohort members was used in the survey. The prevalence of the post-polio syndrome was 28.5% of all paralytic cases (95% confidence interval 24.4-32.6). The risk of post-polio syndrome was significantly higher among patients who sustained substantial permanent impairment after polio and among females. The incidence did not vary with age at acute onset, acute severity, or level of physical activity after recovery. The strongest determinant of post-polio syndrome onset was the length of the interval following the acute illness, with incidence peaking at 30-34 years. Of all cases of post-polio syndrome, 79% reported no major change in impairment status since onset. This study demonstrates that poliomyelitis patients are not equally susceptible to post-polio syndrome within the interval of 30-40 years after the original illness. For syndrome cases, the onset was associated with new neuromuscular symptoms and functional changes but not with major new impairment.

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Mortality in a cohort of 770 workers with potential pentachlorophenol (PCP) exposure was evaluated from 1940 through 1989. The study cohort is a subset of a larger cohort of workers with potential exposure to higher chlorinated dioxins. Total mortality and cancer mortality, in the PCP cohort were slightly lower than expected in comparison to the U.S. white male population. There were 229 total deaths with 242.5 expected (SMR = 94, 95% confidence interval 83–108), and 50 cancer deaths with 52.6 expected (SMR = 95, 95% confidence interval 71–125). In comparison with unexposed employees, the risk ratio for total mortality was 1.03 (95% confidence internal 0.90–1.17), and the risk ratio for all cancer mortality was 0.95 (95% confidence interval 0.71–1.26). In most cause of death categories of a priori interest no deaths were observed in the cohort. A small excess of other and unspecified lymphopoietic cancer deaths was observed but did not appear to be related to exposure. Excesses of deaths due to cancer of the kidney, gastric and duodenal ulcer, cirrhosis of the liver, and all accidents were observed in comparison with the U.S. white male population and with unexposed employees. These were associated with increasing estimated cumulative PCP exposure after lagging exposures by 5 and 15 years. Despite the limited size and the generally favorable total mortality experience of the cohort, it was concluded that cohort members may have incurred increased risk of death due to some specific causes. The risks could not, however, be attributed conclusively to PCP exposure and may have been associated with other occupational and nonoccupational factors. Additional mortality surveillance of this cohort will be performed. © 1996 Wiley‐Liss, Inc.